JP3351169B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a laser printer.
The present invention relates to an image forming apparatus of a type in which a sheet is electrostatically attracted to a transfer drum or a transfer belt and a toner image is transferred onto the attracted sheet.

[0002]

2. Description of the Related Art Image forming apparatuses such as electrophotographic copying machines and laser printers have become more widespread than ever, and in recent years, image forming apparatuses for forming color images have become widespread. Various types of color image forming apparatuses using an electrophotographic method have been proposed, and as one of them, a method using a transfer drum or a transfer belt is known. There are several types of such systems. One of them is to electrostatically adsorb a sheet on a transfer drum or a transfer belt, and apply toner of each color sequentially formed on the electrostatically adsorbed sheet. There is a method of sequentially transferring toner images such that the toner images are superimposed on each other.

FIG. 6 is a schematic diagram showing a schematic structure of a transfer drum and a peripheral portion thereof in a color image forming apparatus employing the above-described method. A photosensitive drum 2 is arranged near the transfer drum 1. The transfer drum 1 and the photosensitive drum 2 rotate in the directions of arrows A and B in synchronization with each other. Around the photosensitive drum 2, a main charger (not shown) and an exposure device (not shown), each of which is shown in the drawing, each of four color toners of black (K), yellow (Y), magenta (M), and cyan (C). The developing device 3 used, a cleaning device (not shown), and the like are provided, and an electrostatic latent image of a color-separated image is sequentially formed on the photosensitive drum 2 and is developed with a toner of a corresponding color. The toner images developed with the toners of the respective colors are sequentially transferred onto the sheet P adsorbed on the outer peripheral surface of the transfer drum 1 so as to overlap each other. The transfer drum 1 is made of polyethylene terephthalate (P
ET) A drum-shaped one made of an insulating film such as an acrylic resin. Around and inside, as shown, a metal chute 4, a transfer corotron 5, a peeling corotron 6, a neutralizing corotron 7, and a fur brush 8 for cleaning. , A backing brush 9 is provided.

[0004] The metal chute 4 transports the paper P
At a position close to the photosensitive drum 2 of the transfer drum 1 and is electrically grounded.
The transfer corotron 5 charges the inner surface of the transfer drum 2 with a charge having a polarity (plus in the case shown) opposite to the polarity (minus in the case shown) of the toner image formed on the photoconductor drum 2, and a metal chute. Paper P guided and transported to
Is electrostatically attracted to the transfer drum 1 and the toner image of the first color (for example, black) on the photosensitive drum 2 is transferred to the paper P. Paper P adsorbed on transfer drum 1
Rotates with the rotation of the transfer drum 1 while being attracted to the transfer drum 1, and reaches the transfer corotron 5 again. At this time, a toner image of the next color (for example, yellow) is formed on the photosensitive drum 2, and the yellow toner image is transferred onto the paper P by the transfer corotron 5. The paper P further rotates with the rotation of the transfer drum 1, and a magenta toner image and a cyan toner image are sequentially transferred onto the paper P in the same manner as described above. In this way, black, yellow,
When the four color toner images of magenta and cyan are transferred, the peeling corotron 6 operates and the transfer corotron 5
With the AC discharge having a bias of the same polarity (positive in the drawing) applied thereto, a charge of the same polarity (positive in the drawing) as the charge on the inner surface of the transfer drum 1 is charged on the paper P on which the developed image has been transferred, The sheet P adsorbed on the transfer drum 1 is peeled off and sent to a fixing device (not shown). The inner and outer surfaces of the transfer drum 1 from which the paper P has been peeled are neutralized by the neutralizing corotron 7. The static elimination corotron 7 is an outer static elimination corotron 71
And an inner static elimination corotron 72, an alternating voltage having a bias of the same polarity (positive in the figure) as the transfer corotron 5 is applied to the outer static elimination corotron 71, and a polarity opposite to the transfer corotron 5 to the inner static elimination corotron 72 ( An AC voltage biased by (−) in the figure is applied, and the inner and outer surfaces are neutralized.

The cleaning fur brush 8 is configured to be able to freely contact and separate from the transfer drum 1, and is located away from the transfer drum 1 as shown in FIG. When the transfer is completed and the paper P is peeled off from the transfer drum 1, the fur brush 8 comes into contact with the transfer drum 2, and the toner, paper dust and the like adhering to the surface thereof are cleaned. The backing brush 9 is provided to prevent the transfer drum 1 from being deformed when the fur brush 8 comes into contact with the transfer drum 1.

Here, one of the troubles that occurs when the paper P is electrostatically attracted to the transfer drum 1 is that the paper P proceeds to the photosensitive drum side without being attracted to the transfer drum 1,
What is called jamming occurs. FIG.
FIG. 5 is a schematic diagram for explaining the cause of occurrence of jamming. In the example shown here, the photosensitive drum 2 side is negatively charged, and a positive charge is supplied from the transfer corotron 5.

At this time, if the leading edge of the paper P is, for example, 2
If it floats slightly, for example, 0 to 30 μm, a discharge occurs in the region D where the float occurs, and a negative charge is generated on the transfer drum 1 side and a positive charge is generated on the paper P side. Then, the paper P is positively charged, attracted to the negatively charged photoconductive drum 2, advances to the photoconductive drum 2 side, and causes jamming.

A method for solving this problem is disclosed in Japanese Patent Laid-Open No. 4-190.
276, JP-A-3-228075, JP-A-3-194578, and the like. The techniques disclosed therein weaken or do not perform the charge accumulation by the transfer corotron 5 when the leading end of the sheet P guided to the metal chute 4 reaches the transfer drum 1 and delay the start of the operation of the transfer corotron, This is a method in which normal charge accumulation is performed by the transfer corotron 5 after the leading end of the paper P has slightly passed.

By doing so, even if the leading end of the sheet P is slightly lifted, no discharge is generated there. Therefore, careless charging of the sheet P and drawing of the sheet P toward the photosensitive drum 2 are prevented. Thus, the occurrence of jamming is prevented.

[0010]

However, if the operation of the transfer corotron 5 is delayed, there is a problem that the paper P is attracted to the photosensitive drum 2 due to another cause and jamming occurs. FIG. 8 is a schematic diagram for explaining another cause of the occurrence of jamming. When the leading end of the paper P reaches a position sandwiched between the transfer drum 1 and the photosensitive drum 2, if the transfer corotron 5 has not yet started to operate, it is attracted to the negative charge of the photosensitive drum 1,
Positive charge flows into the paper P from the grounded metal chute 4, whereby the paper P is positively charged and the paper P is attracted to the photosensitive drum 2, which may cause jamming. Therefore, if the start of the transfer corotron operation is mechanically delayed, there is a limit in preventing the occurrence of jamming.

In view of the above circumstances, it is an object of the present invention to provide an image forming apparatus in which the occurrence of jamming during paper suction is reduced.

[0012]

An image forming apparatus according to the present invention that achieves the above object develops an electrostatic latent image formed on a photoreceptor to form a toner image on the photoreceptor, and forms the toner image on the photoreceptor. The sheet guided by the metal chute and conveyed to a position close to the photoreceptor is detachably electrostatically adsorbed, and is transferred onto the sheet electrostatically adsorbed to a transfer member arranged close to the photoreceptor. In the image forming apparatus, (1) a charger for electrostatically adsorbing a conveyed sheet to a transfer member and transferring a toner image on a photoconductor onto the sheet electrostatically adsorbed to the transfer member; (2) a transfer member Resistance detecting means for directly measuring or indirectly estimating the resistance value of the paper electrostatically attracted to the sheet (3) measuring by the resistance detecting means when the conveyed paper is electrostatically attracted to the transfer body Or, depending on the estimated paper resistance value, When the value is low, its comparison with when the resistance value is high, and further comprising a timing control means for starting operation of the charger at an earlier timing.

Here, the resistance detecting means may be one for estimating the resistance value of the sheet by measuring the temperature and / or humidity.

[0014]

The development described with reference to FIG. 7 in which the sheet P is charged by the discharge and attracted to the photosensitive drum is performed by the sheet P.
Are likely to occur when the resistance value is high, that is, at low temperature and low humidity under environmental conditions. On the other hand, as described with reference to FIG.
Is easily attracted to the photosensitive drum when the sheet P has a low resistance value, that is, when the environment is in a high temperature and high humidity state and the sheet P contains moisture.

The present invention has been completed by paying attention to this point, and directly measures the resistance value of the sheet electrostatically attracted to the transfer body, or indirectly estimates the resistance value using, for example, a thermo-hygrometer. Then, when the resistance value of the sheet is low, the operation of the charger is started at a timing earlier than when the resistance value is high. As a result, the development in which the paper P is charged by the discharge and is attracted to the photosensitive drum described with reference to FIG. 7 and the paper P is charged by the charge flowing from the metal chute described with reference to FIG. As a result, both the development and the development attracted to the photosensitive drum are prevented, and the occurrence rate of jamming is reduced.

[0016]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing a schematic structure of a transfer drum and its peripheral portion in one embodiment of the image forming apparatus of the present invention. Elements corresponding to the elements of the image forming apparatus shown in FIG. 6 are denoted by the same reference numerals as those shown in FIG. 6, and only different points will be described.

In the image forming apparatus shown in FIG. 1, a power supply 51 for applying a voltage to the transfer corotron 5 and a switch 52 for switching whether or not to transmit the voltage of the power supply 51 to the transfer corotron 5 are explicitly shown. Have been. ON / OFF of the switch 52 is controlled by the timing control circuit 20. The timing control circuit 20 includes the temperature and humidity sensor 2
1 is connected, and the timing control circuit 20 guides and transports the sheet P to the metal chute 4 according to the absolute humidity and the relative humidity obtained from the temperature and humidity measured by the temperature and humidity sensor 21. The timing at which a voltage is applied to the transfer corotron 5 when it comes is controlled.

FIG. 2 is a timing chart showing ON and OFF timings of the sheet P and the transfer corotron 5. When transferring the yellow, magenta, and cyan toner images for the second and subsequent colors, excluding the black of the first color, a reference that is delayed by a distance corresponding to the margin of the leading edge of the paper from the time when the leading edge of the paper P arrives at the transfer position. The operation of the transfer corotron 5 is started at time T ₀ , but when the black toner image of the first color is transferred, that is, the sheet P guided and conveyed by the metal chute 4 is electrostatically attracted to the transfer drum 1. When the time is longer than the reference time T ₀ , the paper P
The transfer corotron 5 starts operation at a timing earlier by ΔT, which is equivalent to the leading edge erasing amount.

FIG. 3 is a diagram showing the operation timing of the transfer corotron during the transfer of the first color. As shown in FIG. 1, the image forming apparatus of the present embodiment includes a temperature and humidity sensor 21, and a timing control circuit 20 determines a relative temperature and an absolute value based on the temperature and humidity measured by the temperature and humidity sensor 21. Temperature is required.

In the region where the relative temperature and the absolute temperature are low, the operation of the transfer corotron 5 is started at the reference time T _{0 at} which the leading end of the sheet P has passed the transfer position by the amount of wiping off the leading end. In the region where the relative temperature and the absolute temperature are low, if the operation start timing of the transfer corotron 5 is advanced, jamming is likely to occur due to the cause described with reference to FIG. In this case, the transfer corotron 5 starts operating when the leading edge of the sheet P has passed by the amount of the leading edge erasure, so that the occurrence of jamming is prevented.

Meanwhile, the relative temperature, absolute temperature is high region, in order to prevent the occurrence of jamming by the cause described with reference, earlier timing by ΔT than the reference time T _0, namely paper P transferred to 8 The operation of the transfer corotron 5 is started at the timing when it reaches the position. This also prevents the occurrence of jamming. In the present embodiment, in the region where the relative temperature and the absolute temperature are intermediate, the operation of the transfer corotron 5 is started at a timing earlier by ΔT / 2 than the reference time T ₀ . This is because the temperature and humidity of the environment and the resistance value of the paper P are correlated, but vary considerably. Therefore, when the relative temperature and the absolute temperature are in the intermediate range, the transfer corotron 5 will be started at an intermediate timing. That is.

FIG. 4 is a view showing a schematic structure of a transfer drum and its peripheral portion in another embodiment of the image forming apparatus of the present invention. Only differences from the embodiment shown in FIG. 1 will be described. In this embodiment, the temperature and humidity sensor 21 shown in FIG.
, A resistance value measuring device 22 for directly measuring the resistance value of the paper P is provided. This resistance value measuring device 22 is provided with a pair of electrodes 22a that come into contact with the conveyed paper P, and when the paper P passes through the position of the electrodes 22a, the resistance P between the electrodes 22a is set. Resistance R of
Is measured.

FIG. 5 is a diagram showing the operation timing of the transfer corotron during the transfer of the first color. In the region where the resistance value R is small, the operation of the transfer corotron 5 is started at a timing earlier by ΔT in order to prevent jamming due to the cause described with reference to FIG. 8, and in the region where the resistance value R is large, see FIG. The operation of the transfer corotron 5 is started at a later timing (reference time T ₀ ) to prevent jamming due to the cause described above. In the region where the resistance value R is intermediate, the operation of the transfer corotron 5 is started at a timing earlier by ΔT / 2. The intermediate region is not always necessary, but by providing such an intermediate region, the measurement accuracy of the resistance value measuring device 22 can be reduced.

In the above embodiment, an image forming apparatus provided with a transfer drum has been described. However, the present invention can be applied to an image forming apparatus provided with a transfer belt.

[0025]

As described above, according to the present invention,
Jamming due to both causes described with reference to FIGS. 7 and 8 is prevented, and a highly reliable image forming apparatus having a low jamming rate is configured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic structure of a transfer drum and a peripheral portion thereof in an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a timing chart showing ON and OFF timings of a sheet P and a transfer corotron 5;

FIG. 3 is a diagram illustrating an operation timing of a transfer corotron during transfer of a first color.

FIG. 4 is a view showing a schematic structure of a transfer drum and a peripheral portion thereof in another embodiment of the image forming apparatus of the present invention.

FIG. 5 is a diagram illustrating an operation timing of a transfer corotron during transfer of a first color.

FIG. 6 is a schematic diagram showing a schematic structure of a transfer drum and a peripheral portion of the transfer drum of the color image forming apparatus employing the above-described method.

FIG. 7 is a schematic diagram for explaining the cause of the occurrence of jamming.

FIG. 8 is a schematic diagram for explaining another cause of the occurrence of jamming.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transfer drum 2 Photoreceptor drum 3 Developing device 4 Metal chute 5 Transfer corotron 6 Peeling corotron 7 Static elimination corotron 8 Fur brush for cleaning 9 Backing brush 20 Timing control circuit 21 Temperature / humidity sensor 22 Resistance value measuring device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114 G03G 21/14

Claims (2)

(57) [Claims] An electrostatic latent image formed on a photoreceptor is developed to form a toner image on the photoreceptor, and the toner image is guided by a metal chute to a position close to the photoreceptor. An image forming apparatus for detachably electrostatically adsorbing a conveyed sheet and transferring the conveyed sheet onto a sheet electrostatically adsorbed to a transfer body disposed in close proximity to the photoconductor, wherein the conveyed sheet is transferred to the transfer member. A charger for causing the toner image on the photoreceptor to be transferred onto the sheet electrostatically attracted to the transfer body while causing the sheet to be electrostatically attracted to the transfer body; Resistance detecting means for measuring or indirectly estimating, and when the conveyed sheet is electrostatically attracted to the transfer body, according to the resistance value of the sheet measured or estimated by the resistance detecting means, When the resistance value is low, when the resistance value is high An image forming apparatus comprising: timing control means for starting the operation of the charger at an earlier timing than in the above. 2. The image forming apparatus according to claim 1, wherein said resistance detecting means estimates the resistance value of the sheet by measuring temperature and / or humidity.