JPH04373254A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an optimum charging frequency in response to a transfer frequency of a picture signal contributing to a print speed and a print density. CONSTITUTION:When an output frequency of an oscillation section 14 is increased, an output voltage of an F/V converter 15 increases and a reference voltage inputted to a noninverting input terminal of a comparator 16 is increased. Thus, its output amplifies a charge AC voltage via a gain control section 17 and a voltage amplifier section 18. As a result, the charged AC current is increased and an input at an inverting input terminal of the comparator 16 is gradually increased and when the level is equal to the input to the noninverting input terminal, the entire circuitry acts like a constant current function. Thus, when the charged AC frequency is increased, the charge AC current increases. An oscillating frequency control signal fed to an oscillating section 14 through a signal line L9 is controlled by picture density. That is, since the charged AC frequency is changed in proportion to a transfer clock frequency of a picture signal, and when a print application speed changes, the transfer clock frequency of the picture signal naturally changes and then the charge AC frequency is changed. As the relation between the picture density and the charged AC frequency when the charged AC frequency is sufficiently higher than the picture density, no unevenness of picture due to uneven charge is caused.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention includes a charging means to which an oscillating voltage is applied to charge an image carrier, and an exposure means for exposing the image carrier to printing light by flashing a light emitter in accordance with an image signal. The present invention relates to an image forming apparatus that forms an image using an image forming process means (electrostatic process, electrophotographic process, etc.).

More specifically, it relates to an image forming apparatus such as a laser printer or an LED printer that performs printing exposure on an image carrier by blinking a semiconductor laser or an LED array in response to an image signal.

0003

2. Description of the Related Art Conventionally, in this type of image forming apparatus, a non-contact type corona discharge device that applies a DC voltage or an AC voltage has generally been used as a charging means for applying an electric charge to an image bearing member such as an electrophotographic photoreceptor. However, recently, contact-type charging devices that charge the surface of an image carrier by bringing a charging member applied with DC or AC voltage into contact with the surface of the image carrier have attracted attention and have been put into practical use. There is.

Regarding this contact charging, the present applicant applies an oscillating voltage (a voltage whose voltage value changes periodically over time) to a charging member using a sine wave, a triangular wave, a square wave, a sawtooth wave, and a DC power source that is periodically turned on and off. have previously proposed a method for uniform charging by applying a rectangular wave voltage formed by applying a voltage such as a superimposed voltage of a DC voltage and an AC voltage (for example, Japanese Patent Laid-Open No. 149669/1983). .

[0005]

[Problems to be Solved by the Invention] In the conventional image forming apparatus of this type, even if the DC voltage or AC voltage applied to the charging means is controlled by constant voltage or constant current, the image clock in the printing exposure means The above AC voltage or the frequency of the AC voltage component is not changed according to the printing speed and printing density contributed by the AC voltage, and the AC current is also not changed, and charging unevenness due to the charging AC frequency is avoided during high-density printing. However, there was a problem in which this appeared as unevenness in the formed image. In addition, when the charging AC frequency is increased to prevent image unevenness from appearing, there is also the drawback that the image carrier and the charging member that is in contact with it resonate and emit sound (charging sound). .

The present invention relates to this type of image forming apparatus, and it is an object of the present invention to always provide good images free of image unevenness due to charging unevenness for all image densities.

[0007]

[Means for Solving the Problems] The present invention provides a charging means to which an oscillating voltage is applied to charge an image bearing member, and an exposure means for exposing the image bearing member to printing light by flashing a light emitter in accordance with an image signal. In an image forming apparatus that performs image formation by an image forming process means including: a frequency of an oscillating voltage applied to the charging means in response to a change in a transfer clock frequency of the image signal; An image forming apparatus is characterized in that the current value of the oscillating voltage is changed according to the current value of the oscillating voltage.

[0008]

[Operation] According to the above configuration, the optimum charging AC frequency can be set and controlled according to the transfer clock frequency of the image signal that contributes to the printing speed and printing density, and a good image without unevenness is always formed. becomes possible. Furthermore, by controlling the charging AC current value in accordance with changes in the charging AC frequency, it is possible to maintain charging performance constant without depending on the environment.

[0009]

Embodiments Embodiment 1 (1) Hardware configuration of image forming apparatus FIG. 1 is a schematic diagram of the configuration of an embodiment. The device of this example is a laser printer using an electrophotographic process. A is a hardware unit (image forming unit) of the printer, and 1 to 3 are control units that control this image forming unit.

In the image forming section, reference numeral 9 denotes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as photosensitive drum) as an image carrier, which is rotated counterclockwise as indicated by an arrow.

Reference numeral 6 denotes a contact charging roller serving as charging means for applying a charge to the photosensitive drum. By applying an oscillating voltage, which is a superimposition of a DC voltage and an AC voltage, to the charging roller 6, the surface of the rotating photosensitive drum 9 is charged to a predetermined polarity and potential.

Reference numeral 4 denotes a light emitting unit such as a laser diode that blinks according to the print data, and 5 is a scanner unit including a polygon mirror that rotates with a scanner clock synchronized with the image clock. It constitutes a print exposure section.

The surface of the photoreceptor drum 9 that has been charged by the charging roller 6 is scanned and exposed with laser light by the print exposure units 4 and 5, thereby forming an electrostatic latent image on the surface of the photoreceptor drum 9 corresponding to the desired image information. is formed.

The formed electrostatic latent image is developed with toner by a toner developing device 7. The toner images are then sequentially transferred onto a sheet of paper 10 that is fed from a paper feeding section (not shown) between the photosensitive drum 9 and the transfer device 8 at a predetermined timing.

The paper onto which the toner image has been transferred is conveyed to a fixing device (not shown), where the image is fixed and an image-formed product (print) is formed.
is output as After the toner image has been transferred, the surface of the photoreceptor drum is cleaned by a cleaning device 25 to remove adhered contaminants such as residual toner, and is repeatedly used for image formation.

In the control units 1 to 3, 1 is a host computer, which sends image information data to the printer,
Monitor printer status. Reference numeral 2 denotes a printer controller circuit block including an image controller, an engine controller, etc., which is mounted on the printer body, and includes a print data generation section 11, an image clock generation section 12, and a frequency dividing circuit 13. 3 is a high-voltage power supply circuit block that applies bias to the process equipment of the image forming section, and the oscillation section 14
, F/V converter 15, comparator 16, gain control section 17, voltage amplifier 18, charging DC voltage generation section 1
9, a developing voltage generating section 20 that supplies a developing voltage to the toner developing device 7, a transfer voltage generating section 21 that supplies a transfer voltage to the transfer device 8, and a charging AC current detecting section 22. (2) Control Next, the signal lines connecting the parts 1 to 4 will be explained.

L1 is a signal line for sending image forming information from the host computer 1 to the print data generation section 11 of the printer controller circuit block 2. Although not shown, the printer controller circuit block 2 sends printer information such as image writing timing to the host computer 1.

L3 is a signal line that develops the image forming information into a dot image in the print data generation section 11 and sends a light emitting element ON/OFF signal to the light emitting unit 4, and this light emitting element ON/OFF signal is used at the image writing timing. is synchronized with.

L2 is a signal from the host computer 1 to the image clock generator 12 of the printer controller circuit block 2.
The image clock generator 12 supplies an image clock according to the image density to the print data generator 11, and turns on the light emitting elements generated by the print data generator 11. /OFF signal synchronization signal.

L4 is a signal line which converts the signal generated from the image clock generating section 12 into a scanner clock signal via the frequency dividing circuit 13 and sends it to the scanner unit 5 as a synchronous drive signal. Therefore, the light emitting element ON/OFF signal and the scanner clock signal are always synchronized even if the image density changes.

L5 to L9 are signal lines connecting the printer controller circuit block 2 and the high voltage power supply circuit block 3.

L5 turns on/off the transfer voltage generating section 21
The signal line that changes the polarity, L6 is an AC/
Turn on/off the developing voltage generator 20 that generates the DC superimposed voltage
The signal line L7 is a signal line that turns on/off the charging DC voltage generator 19 or changes the voltage level.

As will be described later, the charging DC voltage of the charging DC voltage generator 19 is superimposed on the charging AC voltage and the signal line L1 is
Output to 0.

L8 is a signal line that turns ON/OFF the oscillation of the oscillation section 14, and controls the oscillation output of the oscillation section 14 as a charging AC output that is amplified by the voltage amplifier 18.

L9 is a signal line that changes the oscillation frequency of the oscillation section 14.

a) The oscillation section 14 has a voltage amplifier 18 and an F/V
An AC waveform is output to the (frequency/voltage) converter 15. I
/V converter 15 is a circuit that converts the output frequency of oscillation section 14 into a voltage. The output of the F/V converter 15 is input to the + input terminal of the comparator 16, and controls the charging AC current value input from the charging AC current detector 22 to the - input terminal. Voltage amplifier 18 and charging DC voltage generator 19
The charging output outputted to the signal line L10 flows to the ground E through the signal line L13 via the charging roller 6 and the photosensitive drum 9.

b) The charged alternating current flowing from the ground E of the charged alternating current detection section 22 is waveform-shaped and rectified to become a direct current voltage proportional to the charged alternating current, which is applied to the comparator 16.
The amplification factor of the voltage amplification section 18 is lowered via the gain control section 17 by the output of the comparator 16 which is input to the negative input terminal of the voltage generator 16 and is output when it is larger than the input to the positive input terminal. Also, if the input to the - input terminal is smaller than the input to the + input terminal, the amplification factor increases and the + input of the comparator 16 increases.
Controlled by constant current based on reference voltage. When a signal for changing the frequency of the oscillation section 14 is input from the printer controller section 2 to the oscillation section via the signal line L9, the frequency of the output of the oscillation section 14 changes.

c) Now, when the charging alternating current is controlled at an arbitrary frequency, when the output frequency of the oscillator 14 increases,
The output voltage of F/V converter 15 also increases, and comparator 1
The reference voltage input to the + input terminal of No. 6 increases. Therefore, the output of the comparator 16 is
, the charging AC voltage is amplified via the voltage amplifying section 18. As a result, the charging alternating current increases, and the -
The input to the input terminal also gradually increases, and when it becomes equal to the input to the + input terminal, constant current operation begins. Therefore, as the charging AC frequency increases, the charging AC current also increases. The relationship between the frequency of this charging alternating current and the current is a value arbitrarily determined by the electrostatic image forming process.

d) The oscillation section 1 is activated by the signal line L9.
The oscillation frequency control signal supplied to 4 is controlled by the image density. That is, the charging AC frequency changes in proportion to the image signal transfer clock frequency, and as the printing acceleration changes, the image signal transfer clock frequency naturally changes, and therefore the charging AC frequency also changes.

Regarding the relationship between image density and charging AC frequency, basically, if the charging AC frequency is sufficiently higher than the image density, image unevenness due to charging unevenness will not appear. For example, at 300 dots per inch (DPI), the paper transport speed is 1
In the case of an inch/second printer, the light emitting element can be turned on and off 300 times per second. Therefore, the charging AC frequency is higher than 300Hz, e.g.
If the frequency is approximately 000 Hz, image unevenness due to uneven charging will not appear.

However, when the frequency is close to 1000 Hz, it is an audible sound and also has a large energy, so it is not suitable for a charging AC frequency. Therefore, charging performance must be satisfied at a frequency as low as possible. Taking image unevenness into consideration, it was confirmed through experiments that good charging performance can be achieved at a charging AC frequency of about 150 Hz with the specifications of the printer described above.

The charging AC frequency also depends on the materials and performance of the photosensitive drum and charging roller. In other words, in a printer of any specification, its charging AC frequency is uniquely determined in order to maintain good charging performance. Therefore, in order to maintain good charging performance in a printer capable of switching image density, the charging AC frequency must also be changed in accordance with the image density. In other words, by adopting a configuration in which the charging frequency increases as the image density increases, it becomes possible to always maintain good charging performance.

e) Furthermore, the charging output load, that is, the load on the charging roller 6 and the photosensitive drum 9, is represented by a series-parallel connection of a resistor and a capacitor in a pseudo manner. In order to keep the charging performance constant, it is necessary to apply a certain peak-to-peak charging AC voltage to the photoreceptor drum 9. However, the resistance of the charging roller 6 usually changes depending on the environment and usage time. Therefore, when the charging AC output is driven at a constant voltage, the peak-to-peak charging AC voltage applied to the photoreceptor drum 6 changes. Therefore, the charging AC output is generally controlled to be a constant current. Furthermore, since the charging AC frequency is changed according to the image density, the peak-to-peak charging AC voltage applied to the photoreceptor drum 6 also changes. Therefore, when the frequency changes, it is necessary to change the charging AC constant current value.

Therefore, as in the present invention, when the image density increases, the charging AC frequency increases, and by increasing the charging AC current, it is possible to always obtain a good image without image unevenness for any image density. .

<Embodiment 2> FIG. 2 is a diagram of a portion of the high-voltage power supply circuit block 3 of a device according to a second embodiment. Components that are the same as those in FIG. 1 are designated by the same reference numerals and repeated explanations will be omitted. Further, signal lines having the same function are given the same reference numerals and are connected to an external circuit having the same configuration as in FIG. 1.

In this embodiment, instead of the charging AC current detection section 22 in the high-voltage power supply circuit block 3 of the apparatus shown in FIG. This is a configuration in which a circuit 23 is provided.

With this configuration, the resistor R and the capacitor C detect the charged alternating current, the rectifier circuit 23 converts the alternating current voltage generated in the resistor R into a direct current voltage, and the comparator 16 converts the F/V in the embodiment shown in FIG. It is compared with a reference voltage Vref supplied instead of the converter 15, and if the DC voltage is lower than the reference voltage Vref, the peak-to-peak charging AC voltage is increased via the gain control unit 17, and vice versa. Maintain a constant current by lowering the current. In other words, charging AC constant current control is performed with the value of the reference voltage Vref fixed.

In this embodiment, as described above, since the circuit for detecting the charging alternating current is a parallel circuit of the resistor R and the capacitor C, the constant current value is determined by the values of the resistor R and the capacitor C. FIG. 3 shows the parallel impedance of the resistor R and the capacitor C when the charging AC frequency is 150 Hz, and the curve I is the AC impedance value of the resistor R and the capacitor C whose impedance characteristics are constant near the frequency of 150 Hz. As the curve changes to curve II and curve III, the impedance change rate near 150 Hz increases.

For example, if the image density is 300DPI and the charging AC frequency is 150Hz, the image density is 400DPI.
Assume that a signal changing to 200 Hz is input to the oscillating unit 14 via the signal line L9, and the charging frequency changes to 200 Hz. In a parallel circuit of a resistor R and a capacitor C having an impedance characteristic of curve III, the charging AC frequency is 150H.
When changing from z to 200Hz, the impedance is approximately 20%
descend. Therefore, if the constant current value is the same as when the image density is 300 DPI, the input to the - input terminal of the comparator 16 will be lower than the input to the + input terminal, and feedback will be generated via the gain control section 17 to increase the charging AC voltage. Control is applied, the charging AC current value increases, and finally the image density is 400 DPI, and the charging AC current value increases by about 20% compared to the charging AC current value at the image density of 300 DPI.

[0040] In this way, by adding a filter circuit having frequency characteristics to the charging alternating current detecting section, the current value changes automatically in accordance with changes in frequency.

As can be inferred from the first and second embodiments, the print controller circuit block 2 is provided with a look-up table that relates image density, charging AC frequency, and charging AC current. It is also possible to perform similar control.

Here, as the waveform of the alternating current voltage, a sine wave, a rectangular wave, a triangular wave, etc. can be used as appropriate. Further, the alternating current voltage includes, for example, a rectangular wave voltage formed by periodically turning on and off a direct current power source. Such an alternating current voltage is a voltage whose voltage value changes periodically.

[0043]

As explained above, according to the present invention, since the charging oscillating voltage frequency and the current amount of the charging oscillating voltage are controlled to always be appropriate values according to the image density, image unevenness due to charging unevenness can be prevented. This has the effect of eliminating the problem and ensuring that good images are always obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a first embodiment device.

FIG. 2 is a diagram of a high-voltage power supply circuit block portion of the second embodiment device.

FIG. 3 is a graph showing the parallel impedance of a resistor R and a capacitor C.

[Explanation of symbols]

4 Light emitting unit 6 Charger 9 Photosensitive drum 12 Image clock generation section 14 Charged AC oscillator

Claims (1)

[Claims] 1. An image is created by an image forming process means including a charging means to which an oscillating voltage is applied to charge the image bearing member, and an exposure means for exposing the image bearing member to print by flashing a light emitter in accordance with an image signal. In an image forming apparatus that executes formation,
changing the frequency of the oscillating voltage applied to the charging means in response to a change in the transfer clock frequency of the image signal;
An image forming apparatus further characterized in that a current value of the oscillating voltage is changed in accordance with the oscillating voltage frequency.