JP4124848B2 - Electrophotographic image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming apparatus.
[0002]
[Prior art]
FIG. 1 is a cross-sectional view of a color image forming apparatus.
[0003]
The apparatus has a digital color image reader unit at the top and a digital color image printer unit at the bottom.
[0004]
In the digital color image reader unit, the original 30 is placed on the original platen glass 31 and exposed and scanned by the exposure lamp 32, whereby the reflected light image from the original 30 is condensed on the full color sensor 34 by the lens 33, and the color color. A decomposed image signal is obtained. The color-separated image signal is processed by a video processing unit (not shown) through an amplification circuit (not shown) and sent to a digital color image printer unit.
[0005]
In the digital color image printer unit, a photosensitive drum 1 as an image carrier is supported rotatably in the direction of an arrow, and a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system 3, and a potential sensor 12 around the photosensitive drum 1. The four developing devices 4y, 4c, 4m, and 4Bk having different colors, the on-drum light amount detecting means 13, the transfer device 5, and the cleaning device 6 are arranged.
[0006]
In the laser exposure optical system 3, an image signal from the digital color image reader unit is converted into an optical signal by a laser output unit (not shown), and the converted laser beam is reflected by the polygon mirror 3a, and the lens 3b and the mirror 3c. The light passes through the photosensitive drum 1 and irradiates the peripheral surface of the photosensitive drum 1.
[0007]
At the time of image formation in the digital color image printer unit, the photosensitive drum 1 is rotated in the direction of the arrow, and the photosensitive drum 1 after being neutralized by the pre-exposure lamp 11 is uniformly charged by the charger 2, and light is emitted for each separated color. The image E is irradiated to form a latent image.
[0008]
Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1, and a toner image using a resin as a base is formed on the photosensitive drum 1. The developing device alternatively approaches the photosensitive drum 1 according to each separation color by the operation of the eccentric cams 24y, 24c, 24m, and 24Bk.
[0009]
Further, the toner image on the photosensitive drum 1 is transferred from the recording material cassette 7 to the recording material supplied to the position facing the photosensitive drum 1 via the transport system 26 and the transfer device 5. In this example, the transfer device 5 includes a transfer drum 5a, a transfer charger 5b, an adsorption charger 5c for electrostatically adsorbing a recording material, an adsorption roller 5g facing the adsorption charger 5c, an inner charger 5d, and an outer charger. A recording material carrying sheet 5f made of a dielectric material is integrally stretched in a cylindrical shape in an opening area of a peripheral surface of a transfer drum 5a that is rotatably supported. The recording material carrying sheet 5f uses a dielectric sheet such as a polycarbonate film.
[0010]
As the transfer drum 5a of the transfer device 5 is rotated, the toner image on the photosensitive drum 1 is transferred onto the recording material carried on the recording material carrying sheet 5f by the transfer charger 5b.
[0011]
In this way, a desired number of color images are transferred to the recording material attracted and conveyed by the recording material carrying sheet 5f to form a full-color image.
[0012]
In the case of full-color image formation, when the transfer of the four color toner images is completed in this way, the recording material is separated from the transfer drum 5a by the action of the separation claw 8a, separation push-up roller 8b, and separation charger 5h, and heat roller fixing is performed. The paper is discharged to the tray 10 through the device 9.
[0013]
On the other hand, after the transfer, the photosensitive drum 1 is subjected to the image forming process again after cleaning the residual toner on the surface with the cleaning device 6.
[0014]
When forming images on both sides of the recording material, the conveyance path switching guide 19 is driven, the recording material discharged from the fixing device 9 is once guided to the reversing path 21a through the conveying vertical path 20, and then the reversing roller. By reverse rotation of 21 b, the rear end when the paper is fed in is retracted in the direction opposite to the fed direction, and is stored in the intermediate tray 22. Thereafter, the recording material taken out from the intermediate tray 22 is guided to the transfer device 5 through the conveying system 26, and an image is formed on the other surface again by the image forming process described above.
[0015]
Further, in order to prevent scattering of powder on the recording material carrier sheet 5f of the transfer drum 5a, adhesion of oil on the recording material, and the like, the brush 14 is opposed to the brush 14 via the recording material carrier sheet 5f. Cleaning is performed by the action of the pack-up brush 15 and the pack-up brush 17 facing the roller 16 via the oil removing roller 16 and the recording material carrying sheet 5f. Such cleaning is performed before or after image formation, and at any time when a jam (paper jam) occurs.
[0016]
Further, in this example, the eccentric cam 25 is operated at a desired timing, and the cam follower 5i integrated with the transfer drum 5a is operated to arbitrarily set the gap between the recording material carrying sheet 5f and the photosensitive drum 1. The configuration can be set to. For example, the distance between the transfer drum and the photosensitive drum is increased during standby or when the power is turned off.
[0017]
FIG. 2 shows a block diagram of a control circuit for a transfer current supplied to the transfer device 5. In the figure, 201 is a high-voltage transformer for generating a transfer current, 202 is digital data (PWM_DATA) input and set in a register, and a counter value repeatedly counting up to a predetermined value is compared with PWM_DATA. A PWM circuit that continuously outputs a rectangular wave with an arbitrary duty responding to the above, 203 is a low-pass filter that smoothes the output of the PWM circuit 202 and converts it into an analog value, and 204 is an analog signal converted by the low-pass filter 203 as a reference. A differential amplifying unit 205 for controlling an output current, that is, a transfer current, flowing on the secondary side of the high-voltage transformer 201 by controlling a current flowing on the primary side of the high-voltage transformer 201 is a current detection resistor.
[0018]
FIG. 3 shows a control state of a current applied to the recording material to be transferred when the toner image on the photosensitive drum is transferred to the recording material on the transfer drum.
[0019]
In order not to weaken the attractive force of the recording material 302 adsorbed to the recording material carrying sheet 5f, the transfer current is passed from the end of the recording material at a predetermined position until the rear end of the marginal portion 303 at the front end reaches the predetermined position. Launch. FIG. 3 shows a transfer current control signal 305 and an effective transfer current 306 for controlling the transfer current in the control circuit (FIG. 2) at this time.
[0020]
At this time, since the recording material carrying sheet 5f is a high resistance body, the current required for transfer is very small. Further, since the recording material carrying sheet 5f is a dielectric, it has some capacitance. Since a very small current is caused to flow through the high-resistance recording material-carrying sheet 5f having this electrostatic capacity, most of the applied current becomes a charging current for the electrostatic capacity at the initial stage of the start-up of the transfer current. There is a slight delay before the effective transfer current necessary for transfer starts. In order for this delay to fall within the marginal portion 303 of the leading edge of the recording material 302, an acceleration current superimposed with a charge current is applied when the transfer current rises, as indicated by reference numeral 305 in FIG.
[0021]
[Problems to be solved by the invention]
When trying to increase the copying and printing speed, the time for supplying the transfer current to the leading edge of the recording material becomes extremely short. Further, in order to make the leading edge margin as small as possible, the time for supplying the transfer current to the leading edge margin of the recording material is further shortened. In order to cope with this, it is necessary to increase the rise and fall times of the transfer current control signal in the control circuit and further increase the effective transfer current.
[0022]
However, in the conventional transfer current control circuit described above, digital data is converted into an analog signal using a single PWM circuit so that the transfer current is suitable for the image area after the leading margin of the recording material. The obtained transfer current control signal is fixed, and it is difficult to increase the rise and fall times of the transfer current control signal in the control circuit and further increase the effective transfer current. If a high-speed D / A converter is used, the transfer current control signal can be increased, but the high-speed D / A converter is expensive and increases the cost of the product.
[0023]
SUMMARY OF THE INVENTION An object of the present invention is to provide a transfer current control apparatus and method in an electrophotographic image forming apparatus that solves the above-described problems.
[0024]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention provides an image carrier on which an image is formed, a recording material carrier that carries a recording material, and the image carrier on the recording material. First generation for generating first data corresponding to a transfer current smaller than the transfer current in the image area of the recording material in order to control the transfer means for transferring the image and the transfer current supplied to the transfer means A circuit, a second generation circuit for generating second data having a larger value than the first data , corresponding to a transfer current in the image area of the recording material, and a transfer current in the image area of the recording material Corresponding to a large transfer current and generating a third data having a value larger than that of the second data, and the first, second and third generating circuits output the first data. 1, 1 of 2nd, 3rd data Selection means for selecting one of the first, second, and third data based on a selection signal for selecting and outputting as a transfer current control signal, and starting up the transfer current The selection means selects the first data in the leading margin area before the image area of the recording material, then selects the third data, and then selects the second data. It is characterized by.
[0025]
Such invention in claim 2, in advance an image forming apparatus according to claim 1, wherein the first, second, third generation circuit includes a first converter for converting the digital data of different that the values respectively to the rectangular wave And second conversion means for converting the output of the first conversion means into an analog signal.
[0026]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the first conversion unit is a PWM circuit that converts the digital data into a pulse width modulation signal, and the second conversion unit is the first conversion unit. It is a low-pass filter for smoothing the output of one conversion means.
[0027]
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the first and third generation circuits include analog signal voltage generation means for generating a voltage of an analog signal, and the second The generation circuit includes a first conversion unit that converts digital data into a rectangular wave, and a second conversion unit that converts an output of the first conversion unit into an analog signal.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 4 is a block diagram of a transfer current control signal generation circuit according to the first embodiment of the present invention.
[0036]
In FIG. 4, 401 is a first PWM circuit that converts first data (PWM_DATA_1) for transfer current control into a PWM rectangular wave, 402 is a low-pass filter that smoothes the output of the first PWM circuit 401 and converts it into an analog signal, Reference numeral 403 denotes a second PWM circuit that converts second data (PWM_DATA_2) for transfer current control into a PWM rectangular wave. Reference numeral 404 denotes a low-pass filter that smoothes the output of the second PWM circuit 403 to convert it into an analog signal. Reference numeral 405 denotes a transfer current. A third PWM circuit 406 converts third data (PWM_DATA_3) for control into a PWM rectangular wave, and 406 is a low-pass filter that smoothes the output of the third PWM circuit 405 and converts it into an analog signal. The first to third PWM circuits have the same configuration and can have the same configuration as the PWM circuit of FIG. The first to third data is digital data.
[0037]
Reference numeral 407 denotes a select signal for selecting one of the output signals from the three low-pass filters, each of which is composed of two 1-bit signals DATA_SEL_0 and DATA_SEL_1. Depending on the combination of the values of these two signals, Configure selection information. A data selector 408 selectively outputs one of the output signals from the three low-pass filters in response to the select signal. A transfer current control signal 409 is output from the data selector 408. This transfer current control signal is input to a transfer high-voltage power supply unit, for example, the differential amplification unit shown in FIG.
[0038]
The first data (PWM_DATA_1) is smaller than the second data (PWM_DATA_2) and the third data (PWM_DATA_3), and the second data (PWM_DATA_2) is smaller than the third data (PWM_DATA_3). The value of the second data (PWM_DATA_2) is a value corresponding to the transfer current supplied to the image area of the recording material.
[0039]
When the transfer current rises, the output signals from the three low-pass filters based on the first to third data are sent to the first data, the third data, the first data by the data selector 408 in response to the select signal 407. 2 is selected in order of data, and a transfer current control signal that rises rapidly as shown in FIG. 3B is output from the data selector. By applying the transfer current in response to the transfer current control signal that suddenly rises in this way to the transfer device, the effective transfer current is as shown in FIG. 3, and the electrostatic capacity of the recording material carrying sheet is charged in a short time, The effective transfer current rises in a very short time.
[0040]
Next, a second embodiment will be described.
[0041]
FIG. 5 shows a circuit block diagram of the second embodiment of the present invention.
[0042]
In FIG. 5, reference numeral 501 denotes a fourth PWM circuit that converts fourth data (PWM_DATA_4) of transfer current control into a PWM rectangular wave, 502 denotes a low-pass filter that smoothes the output of the fourth PWM circuit 501 and converts it into an analog signal, and 503 A fifth PWM circuit that converts fifth data (PWM_DATA_5) of transfer current control into a PWM rectangular wave, 504 is a low-pass filter that smoothes the output of the fifth PWM circuit 503 and converts it into an analog signal, and 505 is a sixth of transfer current control. 506 is a voltage source for generating an analog signal which is the data (ANALOG_DATA1), and 506 is a voltage source for generating an analog signal which is the seventh data (ANALOG_DATA2). The fourth and fifth PWM circuits have the same configuration and can have the same configuration as the PWM circuit of FIG. The fourth and fifth data are digital data. The voltage sources 505 and 506 may be batteries, but may have any other configuration as long as it can generate a predetermined analog voltage.
[0043]
A data selector 508 selectively outputs one of the output signals from the two low-pass filters and the analog signal from the two voltage sources in response to the select signal 407, and 509 is a transfer current output from the data selector 508. It is a control signal. This transfer current control signal is input to, for example, the differential amplifier in FIG.
[0044]
Between the fourth to seventh data, there is a relationship that the fifth data is larger than the sixth data, the fourth data is larger than the fifth data, and the seventh data is larger than the fourth data.
[0045]
When the transfer current rises, the output signals from the two low-pass filters and the signals from the two voltage sources based on the fourth to fifth data are sent by the data selector 508 in response to the select signal 407. Data, seventh data, fourth data, and fifth data are selected in this order, and a transfer current control signal as shown in FIG. 6 is output from the data selector. By applying the transfer current in response to the transfer current control signal that suddenly rises in this way to the transfer device, the electrostatic capacity of the recording material carrying sheet is charged in a short time, and the effective transfer current rises in a very short time.
[0046]
Note that at least one of the first to third data and at least one of the fourth to fifth data in each of the embodiments can be changed according to each process of image formation in the image forming apparatus, By doing so, image formation can be performed more appropriately. In addition, the switching timing of selection by the select signal of the data selector in each of the embodiments can be changed according to each process of image formation in the image forming apparatus. Further, in each of the embodiments, an environment sensor that converts an environment (for example, temperature) around the image forming apparatus into an electrical quantity is provided, and the first to third data are set according to a signal from the environment sensor. And at least one of the fourth to fifth data can be changed, and the switching timing of selection by the select signal of the data selector can be changed.
[0047]
【The invention's effect】
As described above, according to the present invention, the plurality of transfer current control signals can be changed at high speed, and the effective transfer current can be raised in the leading edge margin of the recording material in a short time, thereby speeding up the image forming apparatus. Can be realized. Further, the speed of the apparatus can be increased at a low cost without using an expensive D / A converter. Further, the values of the plurality of transfer current control signals can be changed and the timing of the change can be changed according to each process of image formation or according to the surrounding environment of the image forming apparatus.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an electrophotographic digital color copying machine.
FIG. 2 is a block diagram of a conventional transfer current control circuit.
FIG. 3 is a time chart of a transfer current control signal.
FIG. 4 is a block diagram of a transfer current control signal generating circuit according to the first embodiment of the present invention.
FIG. 5 is a block diagram of a transfer current control signal generating circuit according to a second embodiment of the present invention.
FIG. 6 is a diagram illustrating a transfer current control signal.
[Explanation of symbols]
401, 403, 405 PWM circuit 402, 404, 406 Low-pass filter 408 selector

Claims (4)

An image carrier on which an image is formed;
A recording material carrier for carrying the recording material;
Transfer means for transferring an image of the image carrier to the recording material;
A first generation circuit for generating first data corresponding to a transfer current smaller than a transfer current in an image area of the recording material in order to control a transfer current supplied to the transfer unit;
A second generation circuit for generating a second data having a value larger than the first data corresponding to a transfer current in the image area of the recording material ;
A third generation circuit for generating third data having a value larger than the second data corresponding to a transfer current larger than the transfer current in the image region of the recording material ;
Based on a selection signal for selecting one of the first, second, and third data output from the first, second, and third generation circuits, the first, second, and third Selecting means for selecting one of the data and outputting as a transfer current control signal;
With
When the transfer current is raised, the selection unit selects the first data in the leading edge blank area in front of the image area of the recording material, then selects the third data, and then the first data. 2. An image forming apparatus, wherein data 2 is selected. It said first, second, third generation circuit includes a first converting means for converting the digital data of different that the values respectively to the rectangular wave, a second conversion means for converting an output of said first converting means into an analog signal The image forming apparatus according to claim 1, further comprising:   The first conversion means is a PWM circuit for converting the digital data into a pulse width modulation signal, and the second conversion means is a low-pass filter for smoothing the output of the first conversion means. The image forming apparatus according to claim 2. The first and third generation circuits include analog signal voltage generation means for generating a voltage of an analog signal, and the second generation circuit includes first conversion means for converting digital data into a rectangular wave, and the first The image forming apparatus according to claim 1, further comprising: a second conversion unit that converts an output of the one conversion unit into an analog signal.

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