JP4482182B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using electrophotographic technology, such as a copying machine, a printer, a printing machine, and a fax.
[0002]
[Prior art]
In an image forming apparatus using an electrophotographic technique, a toner is transferred from a toner image carrier to a recording medium by applying a charge having a polarity opposite to that of the toner to the back surface of the recording medium. The toner is electrostatically attracted to the recording medium and transferred by the charge applied to the back surface of the recording medium. The charge on the back surface of the recording medium does not easily disappear, and remains on the back surface of the recording medium after the transfer of the toner. Therefore, if the process proceeds as it is, the recording medium is electrostatically attracted to the toner image carrier by this charge, and jamming occurs in the apparatus without being peeled off. In order to avoid such obstacles, many image forming apparatuses using an electrophotographic process are equipped with a mechanism for discharging the recording medium after transfer. Among them, the AC static elimination mechanism that performs static elimination by irradiating the back surface of the recording medium with the electric charge generated by the discharge of the corona wire to which an AC voltage is applied is widely used because it can remove the recording medium without contact and has high reliability. ing. In particular, in an image forming apparatus using a photosensitive drum having a large diameter, such as a high-speed copying machine, the AC static eliminator has a great effect in peeling off a recording medium having low rigidity such as paper, and greatly improves the reliability of the apparatus. Has contributed.
[0003]
By the way, the AC static eliminator alternately generates positive and negative corona discharges, and does not eliminate the charge on the back surface of the recording medium in a strict sense. The AC static eliminator has a property of setting the back surface of the recording medium to be neutralized to a specified potential. Therefore, the recording medium is peeled off by setting the charge (potential) on the back surface of the recording medium provided by the transfer means to a charge amount (potential) that can be peeled off by the gravity and rigidity of the recording medium. In order to peel off the recording medium, it is necessary to make the potential on the back surface of the recording medium equal to the potential on the surface of the toner carrier. At this time, since the electric field is zero on the recording medium, the attraction force does not work, so that the leading edge of the recording medium is peeled off from the toner image carrier by the rigidity of the recording medium and is conveyed to the fixing device on the upstream side. .
[0004]
Therefore, control is performed to vary the AC voltage value applied to the AC static eliminator and the superimposed DC offset voltage depending on the environment and the printing mode such as single-sided or double-sided. As an apparatus of the same type, there is an image forming apparatus described in JP-A-10-63108.
[0005]
[Problems to be solved by the invention]
Various electric processes usually exist in the toner image carrier. For example, when the toner image carrier is a photoconductor, there are a charger, a developer, a pre-transfer charger, and the like, and charges are injected from these processes. Further, even when the toner image carrier is an intermediate transfer member used in a color image forming apparatus, charges are similarly injected from a transfer portion of toner from a photosensitive member, a pre-transfer charger, or the like. For this reason, these charges remain on the surface of the toner carrying member, and an electric potential is generated in the charge removing portion. At this time, when the recording medium is peeled from the photosensitive member, since the photosensitive member has a high resistance, there is little fluctuation in the potential of the surface of the photosensitive member due to environmental fluctuations and apparatus variations. However, if the toner image carrier is a resistor (10 M to 1000 GΩcm) such as an intermediate transfer member, the resistance value changes with respect to environmental fluctuations, and as a result, the potential on the surface of the toner carrier varies. Become. This fluctuation of the potential on the surface of the toner image carrier causes a major problem in the peeling of the recording medium.
[0006]
For example, when the peeling current is low, the paper is not peeled off, and jamming is likely to occur. When the peeling current is high, the toner is retransferred to the toner carrier and the print quality is deteriorated. Is more likely to occur.
[0007]
Further, if the peeling current is increased in order to surely peel off the recording medium at the front end, retransfer at the rear end of the paper is likely to occur, resulting in a decrease in print quality.
[0008]
In particular, in a double-sided image forming apparatus in which a toner image is transferred and fixed on the surface of the recording medium, and then the recording medium is reversed and the toner image is transferred and fixed on the back surface. Since the properties of the paper are different at the time of transferring the toner image, the occurrence of a problem that the paper is not peeled off and a jam occurs or the toner is re-transferred and the print quality is deteriorated becomes remarkable. .
[0009]
[Means for Solving the Problems]
The present invention has been devised to solve the above-described problems, and a toner image carrier that holds a toner image and a transfer unit that electrostatically transfers the toner image on the toner image carrier to a recording medium. And an image forming apparatus having a peeling unit for discharging the charge applied to the back surface of the recording medium by the transfer unit and peeling the recording medium from the toner image carrier. In addition, when printing on the front surface, back surface, and both surfaces of the recording medium, the variable control is performed when transferring the toner image on the front surface to the recording medium and transferring the toner image on the back surface. .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of a color laser printer will be described with reference to the drawings for the electrophotographic apparatus of the present invention. FIG. 4 is a vertical side view of the color laser printer. The photoreceptor belt 1 as a photoreceptor is uniformly charged by the charger 3 while being rotated around the guide rollers 2a to 2e at a constant speed. Thereafter, exposure is performed by a laser beam 4a (not shown) emitted from the exposure device 4 according to the image signal of each color, and electrostatic latent images corresponding to the respective colors are sequentially formed, and colors corresponding to the four developing devices 5Y, 5M, 5C, and 5K. The electrostatic latent images are sequentially developed by a developing device using the developer, and toner images of respective colors are formed. The toner images of the respective colors on the surface of the photoreceptor belt 1 are transferred onto the surface of the intermediate transfer drum 6 that is an intermediate transfer body that rotates synchronously while being in contact with the surface of the photoreceptor belt 1. A color toner image is formed above.
[0011]
The paper 8 as a recording medium accumulated in the paper feed cassette 7 is extracted and conveyed by the paper feed roller 9 and sent to the registration roller 10, and the color toner image on the surface of the paper preparation and intermediate transfer drum 6 and the conveyance timing are adjusted. After the alignment control, the sheet is fed toward the transfer roller 11.
[0012]
The toner image of a plurality of colors formed on the transfer drum 5 is recharged by the drum charger 14.
[0013]
The transfer roller 11 constitutes a part of a transfer device, and applies a mechanical pressing force and a transfer electric field from the back surface thereof while bringing the fed paper 8 into contact with the intermediate transfer drum 6, whereby the intermediate transfer drum 6 Transfer the color toner image on the surface to the paper 8. The transfer roller 11 is pulled up by the transfer roller contact / separation device 12 so as not to act in the process of transferring the color toner image on the photosensitive belt 1 onto the surface of the intermediate transfer drum 6 to form a color toner image. The color toner image is pushed out toward the intermediate transfer drum 6 so as to act in the process of completion and transfer to the paper 8. A transfer voltage applied to the transfer roller 11 to generate a transfer electric field is supplied from a high voltage power supply 13 (not shown).
[0014]
Similarly, the AC static eliminator 14, which is a static eliminator that generates an AC corona, is similarly supplied with an AC voltage for static elimination from the high-voltage power supply 13 that can arbitrarily change the output voltage according to the duty ratio of the input signal, etc. The sheet 8 is peeled off from the intermediate transfer drum 6 by neutralizing the charge remaining on the back surface of the sheet 8 to which the color toner image has been transferred and neutralizing the charge. The paper 8 peeled from the intermediate transfer drum 6 is sent to the fixing device 15, and the color toner image is thermally fixed on the surface of the paper 8 while passing through the heat roller 15 b in the fixing device 15. The heat roller 15b is heated to a fixable temperature by energizing the built-in heating element 18.
[0015]
The paper 8 on which the color toner image is thermally fixed is selected to be conveyed to the double-sided paper feeding mechanism 100 by the paper discharge port switching lever 27 or discharged onto the paper discharge tray 23 via the paper discharge roller 22. . The paper 8 transported to the double-sided paper feed mechanism is transported along the transport path formed by the paper guide 101 by the transport roller 103 and enters the reverse rotation unit 102. After all the paper 8 is transported to the reversing unit 102, the transport roller 104 reverses the rotation direction and is fed again from the duplex paper feed mechanism discharge port 104 to the engine unit. The fed paper 8 is in a state where the front and back sides are reversed and printing on the back side is possible. Thereafter, the paper passes through the fixing device 15 again through the above-described printing process, and is discharged onto the paper discharge tray 23 through the paper discharge roller 22 by the paper discharge port switching lever 27.
[0016]
The belt cleaner 25 cleans the toner remaining on the surface of the photoreceptor belt 1, and the drum cleaner 24 cleans the toner remaining on the surface of the intermediate transfer drum 6. The drum cleaner 24 is pulled up so that the cleaning operation does not work in the process of repeatedly transferring the single color toner image to the surface of the intermediate transfer drum 6 to form the color toner image, and transfers the completed color toner image to the paper 8. It is pressed so as to act on the surface of the intermediate transfer drum 6 later.
[0017]
By the way, in the case of the color printer of this embodiment, since various processes exist around the intermediate transfer drum 6, the surface of the intermediate transfer drum 6 receives electric charge injection and is charged. In particular, the negative charge of the drum charger 14 is greatly affected, and the surface of the intermediate transfer drum 6 is negatively charged. Further, since the resistance of the intermediate transfer drum 6 changes depending on the environmental conditions, the surface potential thereof is likely to fluctuate with respect to the environmental change. In a low temperature / low humidity environment, the resistance of the intermediate transfer drum 6 becomes high, and therefore minus several hundreds. On the other hand, in a high temperature / high humidity environment, the resistance becomes low, so it becomes about 0V. For this reason, the potentials on the back of the sheet and the surface of the intermediate transfer drum 6 as described in the prior art do not match, and jamming may occur. Further, since the intermediate transfer drum 6 is required to have a circumference longer than the length of the paper to be printed, the diameter inevitably increases. For this reason, the peeling of the sheet from the intermediate transfer drum 6 cannot be expected to be a natural peeling due to the sheet rigidity, and the stability is low.
[0018]
In order to solve this problem, the following peeling mechanism has been invented. In FIG. 3, the structure of the peeling mechanism of this invention is shown. The peeling mechanism of the present invention has an AC static eliminator 14, an AC power source 29, a voltage control unit 30, and a CPU 31. The CPU 31 also controls the entire image forming apparatus. The AC static eliminator 14 includes a corona wire and a shield case, and has the same structure as the corotron charger. An AC power supply 29 is connected to the corona wire. The AC power supply 29 is a sine wave having an amplitude of 7 to 14 kV and a frequency of 300 Hz to 2 kHz (which may be a triangular wave or a square wave), and can superimpose a DC voltage of 0 to 1 kV. Alternatively, one part can be varied.
[0019]
The voltage control unit 30 has a function of determining a value to be output by the AC power supply 29 based on control from the CPU 31 and controlling the AC power supply 29. Here, how the voltage control unit 30 determines the output will be described. As described in the prior art, in order to peel off the paper, it is necessary to reduce the potential difference between the surface potential of the intermediate transfer drum 6 and the potential on the back of the paper at the paper peeling portion.
[0020]
The voltage control unit 30 controls all or part of the voltage amplitude, DC superimposed voltage value, and AC voltage on / off time ratio, which are output parameters of the AC power supply 29, and the AC static eliminator 14 is charged. Control the potential on the back of the paper. When the voltage control unit 30 controls the amplitude value of the AC voltage, as the amplitude is increased, the back side of the sheet is more negatively charged. When controlling the DC superimposed voltage, the voltage is set to negative. When shifted, the back side of the paper is similarly more negatively charged. When the on / off time of the AC voltage is controlled, the back surface of the sheet is strongly negatively charged as the on time is increased. By using these methods, the potential on the back side of the paper can be controlled.
[0021]
The CPU 31 switches the voltage control pattern and controls the output of the AC power supply 29 based on information on whether the current printing mode is single-sided, double-sided front or back. is there. As described above, the voltage control pattern controls all or part of the voltage amplitude, the DC superimposed voltage value, and the AC voltage on / off time ratio, which are output parameters of the AC power supply 29, to control AC. The electric potential of the back side of the sheet charged by the electric device 14 is controlled. Further, the CPU changes the pattern based on information from a temperature sensor and a humidity sensor (not shown), control information for transfer control, and control information for the drum charger.
[0022]
Here, a case where the DC superimposed voltage value is changed in the power control pattern will be described.
[0023]
When printing on the surface of single-sided printing or double-sided printing, the CPU 31 performs control based on the following control pattern.
[0024]
The following description will be made on the assumption that appropriate peeling can be performed with a DC superimposed voltage value of −600 V when standard paper is used in the printer apparatus at room temperature and humidity.
2 and 3 are diagrams showing voltage control to the peeling apparatus of the present invention.
[0025]
When the leading edge of the sheet is at the position of the peeling device, the AC power supply is turned on and a voltage is applied to the peeling device. The DC superimposed voltage value applied at this time is −600 V at which appropriate peeling can be performed.
[0026]
By applying this voltage, the sheet is peeled off from the transfer drum surface by its rigidity. The peeled sheet is conveyed toward the fixing device 6 by the conveying force from the transfer drum and the transfer device.
[0027]
Here, the distance between the peeling device and the fixing device is L. When the sheet is conveyed by the distance L, the leading edge of the sheet reaches the fixing device. As described above, the fixing device 6 is a device that sandwiches a sheet by two heat rollers and fixes the sheet by its heat and pressure, and can give a sufficient conveying force to the sheet. For this reason, when the leading edge of the sheet reaches the fixing device, a force for peeling from the transfer drum is applied by the conveying force of the fixing device.
[0028]
However, if the voltage applied to the peeling device is turned off, the peeling position may move above the drum and the marking screen may touch the peeling claw. Further, if the voltage of the peeling device is left as it is, the toner may be retransferred.
[0029]
Therefore, the DC superimposed voltage value applied to the peeling device is reduced to -300 V, at which the peeling force is halved.
[0030]
This makes it possible to prevent retransfer and the like while giving a sufficient peeling force.
[0031]
Furthermore, the following example is given as another control pattern.
[0032]
When peeling the leading edge of the paper, if the peeling is possible due to the rigidity of the paper, if the peeling is possible, the DC leading voltage value is between the distance 0.1L and the distance 0.3L from the leading edge of the peeling device. Is −500V, and the DC superimposed voltage value after the distance transport is −600V. After the distance L is conveyed, the pattern is set to −300V.
[0033]
By switching between these two patterns depending on the type of paper and environmental conditions, it is possible to obtain a good print image without stable peeling and retransfer.
[0034]
Next, at the time of printing on the back side, control is performed according to the following pattern.
[0035]
When printing on the back side, the paper curls by passing through the fixing device, and the rigidity of the paper changes due to toner adhering to one side.
[0036]
Therefore, −600 V is applied while the leading end of the sheet is a distance L from the position of the peeling device to the fixing device. Next, after the leading edge of the sheet reaches the fixing device, the DC superimposed voltage value applied to the peeling device is reduced to -300 V, which reduces the peeling force by half. Further, the trailing edge of the paper is easily peeled off due to curling, and the DC superimposed voltage value is further reduced to −150 V, which reduces the peeling force by half.
[0037]
Thereby, it is possible to obtain a good print image without stable peeling and retransfer. Further, in the control during printing on the back side, a second pattern on the front side that weakens the DC superposed voltage value when the front end of the sheet is between the distance of 0.1 L and the distance of 0.3 L from the head of the peeling device may be used.
[0038]
These patterns are switched by selecting an optimum pattern according to the environmental conditions of the printer and taking a DC superimposed voltage value as an example. However, this value changes depending on the environmental conditions.
[0039]
Further, in this example, the pattern in which the DC superimposed voltage value is varied is shown. However, all or part of the voltage amplitude, the DC superimposed voltage value, and the AC voltage on / off time ratio, which are output parameters of the AC power supply 29, are shown. It is possible to create a pattern by controlling.
[0040]
Further, the following control may be added. At the time of surface printing, the CPU measures the image printing rate. The image printing rate is a measure of the amount of toner adhering to the paper surface by measuring the on / off ratio of laser light during development of each color. When the printing rate is high, the rigidity of the paper becomes high, and further, the curling is caused by the adhesion of the toner. Therefore, it is possible to use a pattern in the case of paper with higher rigidity.
[0041]
【The invention's effect】
According to the present invention, it is possible to stably carry out static elimination of a recording medium even when environmental conditions change, and it is possible to provide a highly reliable image forming apparatus. In particular, it greatly contributes to improving the reliability of a color image forming apparatus using an intermediate transfer drum having a large diameter.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an image forming apparatus of the present invention.
FIG. 2 shows an example of a control voltage to the peeling apparatus of the present invention.
FIG. 3 shows another example of the control voltage to the peeling apparatus of the present invention.
FIG. 4 is a longitudinal sectional view of the image forming apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photosensitive belt, 3 ... Charger, 4 ... Exposure apparatus, 4c ... Scanner motor, 5Y, 5M, 5C, 5K ... Developer, 6 ... Transfer drum, 7 ... Paper feed cassette, 8 ... Paper, 9 ... Paper feed Roller, 10 ... Registration roller, 11 ... Transfer roller, 13 ... High voltage power supply,
DESCRIPTION OF SYMBOLS 14 ... AC static eliminator, 15 ... Fixing device, 18 ... Heat generating body, 20 ... Main motor, 21 ... Development motor, 22 ... Paper discharge roller, 23 ... Paper discharge tray, 24 ... Drum cleaner, 25 ... Belt cleaner, 29 ... AC power source, 30 ... voltage control unit, 31 ... CPU,
DESCRIPTION OF SYMBOLS 100 ... Double-sided printing mechanism, 101 ... Paper guide, 102 ... Reverse rotation part, 103 ... Conveyance roller.

Claims (7)

A toner carrier for holding a toner image; transfer means for electrostatically transferring the toner image on the toner carrier to a recording medium; and removing charges applied to the recording medium by the transfer means to remove the recording medium. Peeling means for peeling from the toner carrier, a paper feed cassette arranged below the toner carrier to hold a recording medium, and a recording medium placed above the peeling means and peeled from the toner image carrier In the electrophotographic apparatus having a fixing device for fixing the toner image on the recording medium and capable of recording on both sides of the recording medium by reversing the recording medium after recording, the electrophotographic apparatus controls at least the output of the peeling means The control unit has two control patterns, and the output of the peeling unit is controlled by different control patterns for the front side print and the back side print of the recording medium. A first interval from the start of the output of the stripping means and the leading end of the recording medium, and a section to the tip of the recording medium from the first section end arrives at the fixing device and the central portion of the recording medium, The section from the time when the leading edge of the recording medium arrives at the fixing device to the end of the output is defined as the trailing edge of the recording medium, and in the printing on the back surface, the output of the peeling means is output during charge neutralization of the recording medium. causes a change such that the central portion>tip> rear end of the recording medium, before the end of the output of the previous SL rear part Ji reduced output further control pattern is changed to four stages of non-0V An electrophotographic apparatus controlled by the above.   2. The electrophotographic apparatus according to claim 1, wherein the toner carrying member is an intermediate transfer drum, and the transfer unit is a transfer roller.   3. The electrophotographic apparatus according to claim 2, wherein when the distance of the central portion is L, the distance of the tip is 0.1L to 0.3L.   2. An electrophotographic apparatus according to claim 1, wherein said peeling means is an AC static eliminator in which an AC voltage is applied to a corotron charger.   5. The electrophotographic apparatus according to claim 4, wherein the control of the output of the peeling means changes a DC superimposed voltage value.   6. The electrophotographic apparatus according to claim 5, wherein the output of the peeling means changes the voltage amplitude.   5. The electrophotographic apparatus according to claim 4, wherein the control of the output of the peeling means changes the ratio of the on / off time of the AC voltage.

Images