JPH11194558A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of adjusting the density of an image, capable of suppressing unnecessary noise and higher harmonic waves, and excellent in reliability. SOLUTION: The set value of an image density is read by a CPU 5 in a control circuit 4, the conducting phase angle of a document illuminating lamp corresponding to it is calculated and compared with the prescribed angle in a memory 6. If the calculated phase angle is smaller than the prescribed angle, power is fed to a drive circuit 3 at the calculated angle, and a development bias value is fed at a predetermined value. If the calculated angle is larger than the prescribed angle, the conducting phase angle is set to the prescribed angle, the DC component value of the development bias value corresponding to the difference from the prescribed angle is calculated, and the development bias is fed from a high-voltage power supply 7 at the DC component value for an image forming action.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a toner image on a recording material, and more particularly to an image forming apparatus having a feature in image density control.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
In the image density control applied, a light source such as a halogen lamp is often used as a document illuminating means, and the density of the formed image is changed by changing the light amount of the document illuminating lamp or the bias value of the developing bias. It is configured to obtain an image of a desired density.

[0003]

However, in such a conventional example, in order to reduce the amount of light of the original illumination lamp and increase the image density, the conduction phase angle of the drive control of the original illumination lamp is increased to increase the lamp. A method of reducing the power is used. In this case, a large amount of noise is generated at the time of driving the illumination lamp, and a large filter circuit is required to remove the noise, resulting in an increase in cost.

The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to adjust the density of a toner image and suppress unnecessary noise and harmonics. An object of the present invention is to provide an image forming apparatus having excellent reliability.

[0005]

In order to achieve the above object, according to the present invention, an image carrier is charged by charging means, and an illuminated original image is exposed to form a latent image on the image carrier. In an image forming apparatus which develops a latent image by applying a developing bias to a formed and developed developing means and transfers the developed image to a recording material, setting of image density of an image formed on the recording material is performed by manuscript illumination. When the light amount of the document illumination is equal to or more than a predetermined amount, the image density is controlled by the light amount of the original illumination, and when the light amount of the original illumination is equal to or less than the predetermined amount, the light amount of the original illumination is set to a predetermined amount and the DC component of the developing bias is adjusted. The image density is controlled by at least one of a change and a change of a bias value supplied to the charging unit.

Therefore, in the image forming apparatus configured as described above, the density of the image can be adjusted to the set density, and unnecessary noise and harmonics can be suppressed.

Further, the light quantity of the document illumination is controlled by the phase control of the AC power supply, and a predetermined quantity of the light quantity of the document illumination is expressed as a predetermined angle in the conduction phase angle, and the light quantity of the document illumination corresponding to the set image density is obtained. The conduction phase angle in the phase control is calculated, and if the calculated angle is equal to or smaller than a predetermined angle, the conduction phase angle is set to the calculated angle, and if the calculated angle is equal to or larger than the predetermined angle, the conduction phase angle is set to the predetermined angle. It is preferable to control the image density formed on the recording material by the DC component value of the developing bias corresponding to the difference between the angle and the predetermined angle.

Thus, the density of the image can be adjusted to the set density, and unnecessary noise and harmonics can be suppressed.

Further, the light quantity of the document illumination is controlled by the phase control of the AC power supply, and the predetermined quantity of the light quantity of the document illumination is expressed as a predetermined angle in the conduction phase angle, and is calculated from the light quantity of the document illumination corresponding to the set image density. The conduction phase angle in the phase control is calculated, and if the calculated angle is equal to or smaller than a predetermined angle, the conduction phase angle is set to the calculated angle, and if the calculated angle is equal to or larger than the predetermined angle, the conduction phase angle is set to the predetermined angle. It is preferable to control the image density formed on the recording material by a bias value supplied to the charging unit corresponding to a difference between the angle and the predetermined angle.

Thus, the density of the image can be adjusted to the set density, and unnecessary noise and harmonics can be suppressed.

[0011]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The material, shape, relative arrangement, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

FIG. 2 is a schematic diagram of an image forming apparatus according to the present embodiment.

In FIG. 2, reference numeral 12 denotes a platen glass on which a document is placed, and 13 denotes a pressure plate for pressing the document. First, the photosensitive drum 16 serving as an image carrier is
8 is charged. The original is illuminated by the original illumination lamp 11 and the reflected light image forms an electrostatic latent image on the photosensitive drum 16.

In this embodiment, a halogen lamp is used as the document illumination lamp 11. The above-described electrostatic latent image is housed in a developing device 14 as a developing unit, and is visualized by a toner made of a resin or the like that softens and melts when heated. The visualized toner image is transferred onto a recording material by a transfer / separation charger 15, heated and fixed by a fixing device 17, and discharged.

FIG. 1 is a control block diagram of the image forming apparatus according to the present embodiment. Reference numeral 1 denotes an input AC power supply of the image forming apparatus, and reference numeral 2 denotes a thermal fuse for protecting the document illumination lamp 11. Reference numeral 3 denotes a drive circuit for supplying power to the original illumination lamp, 4 denotes a control circuit for controlling the entire image forming apparatus, and a CPU (microcomputer) 5,
It is composed of a memory 6 and the like.

Reference numeral 7 denotes a developing sleeve 8 in the developing device 14.
Further, a high-voltage power supply for supplying a developing bias is supplied as a power supply having a waveform in which a DC component is superimposed on a rectangular wave as shown in FIG.

Reference numeral 9 denotes a charger as a charging means for applying a potential on the surface of the photoconductor 16, and supplies a DC component power from the high voltage power supply 7 at a voltage value corresponding to a control value.

Here, the image density can be changed by changing the DC component value of the developing bias as shown in FIG. 5, or by changing the bias value supplied to the charger.

That is, in this image forming apparatus, for example, the DC component value of the developing bias is changed from -200 V to -10.
By setting the voltage to 0 V or changing the bias value supplied to the charger from -800 V to -850 V, an image with a high density can be obtained.

Reference numeral 10 denotes an operation unit for setting various image forming conditions of the image forming apparatus, that is, the number of images to be formed, the size of a recording material, the density of an image, and the like.

FIG. 3 is a diagram showing the details of the drive circuit 3 described above. Reference numeral 19 denotes a transformer (not shown) for detecting the lighting voltage of the document illumination lamp 11, and the output thereof is rectified and smoothed according to the lighting voltage. This is a zero-cross detection circuit including a circuit (not shown) for converting to a DC analog voltage and a photocoupler (not shown) for outputting a pulse at the zero-cross timing of the AC input.

Reference numeral 20 denotes a triac for controlling the power of the original illumination lamp 11, and reference numeral 21 denotes a snubber and a capacitor 2 for absorbing the switching noise of the triac 20.
2. The choke coil 23 is a filter circuit for absorbing noise.

Reference numeral 24 denotes a phototriac coupler for generating a trigger pulse for igniting the above-described triac 20, and for isolating the primary AC side and the secondary control side.

Next, the operation of the control circuit 4 will be described. When the original illumination lamp 11 is turned on, a trigger pulse 25 is output from the CPU 5 in the control circuit to the drive circuit 3.

The timing of the trigger pulse 25 is determined based on the zero-crossing detection signal 27 sent from the above-mentioned zero-crossing detection circuit 19 by determining the timing of the conduction phase angle so that the AC power supply has a predetermined power.
A trigger pulse 25 is output at the timing set by a timer (not shown) provided in 5.

By performing the above-described phase control, it is possible to form an image while keeping the light amount of the original illumination lamp 11 constant.

Here, when the image density is set high by the operation unit 10, the CPU 5 in the control circuit 4 reads the image density setting value and calculates the conduction phase angle of the original illumination lamp 11 corresponding to the setting value. You.

The calculated angle is compared with a predetermined angle in the memory 6. If the calculated angle is smaller than the predetermined angle, the power is supplied to the drive circuit 3 at the calculated angle to turn on the original illumination lamp 11. The developing bias value is supplied from the high-voltage power supply 7 at a predetermined value in the memory 6, and a desired image is obtained by performing an image forming operation.

If the calculated angle is larger than the predetermined angle, the conduction phase angle is set to the predetermined angle, and the DC component value of the developing bias corresponding to the difference from the predetermined angle is calculated. By performing an image forming operation by supplying a developing bias from the high voltage power supply 7, an image having a desired set density is obtained.

As shown in FIG. 5, the developing bias is V
_An image forming operation is performed by superimposing a negative potential of a DC component on a rectangular wave having _pp of 1 kV and a frequency of about 2 kHz.

The density of the image can be adjusted by changing the negative potential of the DC component. For example, if the current DC component is -200 V (density 1), an image with a high density can be obtained by changing the DC component to -180 V (density 2).

As described above, even when the bias value supplied to the charger 18 is changed, a desired image can be obtained by performing the same control as when changing the developing bias.

FIG. 4 shows a flowchart of this control.

By the way, in the case of the conventional example, as described above, the trigger pulse 25 to the drive circuit 3 is changed from the state of FIG. 6A to the state of FIG. 6B as shown in FIG. By performing the control, the light amount of the document illumination lamp 11 can be reduced, and the density of the output image can be increased.

However, in this case, as shown in FIG. 6B, the trigger timing for applying the document illumination lamp 11 starts at a portion where the input voltage is high, so that the noise component at the time of triggering and The harmonic components of the current increase.

Here, a predetermined angle of the conduction phase angle is set, and when the image density is set below this predetermined angle (in a direction in which the image density decreases), the phase of the conduction phase angle is changed to change the phase of the original illumination lamp 11. The image density can be reduced by increasing the amount of light.

On the other hand, when the density setting is set to a predetermined angle or more (in the direction in which the image density is high), the DC of the developing bias corresponding to the light amount decrease (light amount difference) from the predetermined angle is set.
By changing the component value or the bias value supplied to the charger 18, the image density can be increased, and the noise component and the harmonic component can be reduced.

[0038]

According to the present invention, the image density of an image formed on a recording material is controlled by controlling the image density with the light intensity of the original illumination when the light intensity of the original illumination is equal to or more than a predetermined amount. When the light amount is equal to or less than the predetermined amount, the light amount of the original illumination is set to the predetermined amount, and the image density is controlled by at least one of the change of the DC component of the developing bias and the change of the bias value supplied to the charging unit. Thus, the density of the image can be adjusted to the set density, and unnecessary noise and harmonics can be suppressed.

The light quantity of the original illumination is controlled by the phase control of the AC power supply, a predetermined quantity of the light quantity of the original illumination is expressed as a predetermined angle in the conduction phase angle, and the phase control is performed based on the light quantity of the original illumination corresponding to the set image density. Calculate the conduction phase angle in, if the calculated angle is less than or equal to a predetermined angle, set the conduction phase angle to the calculated angle,
When the calculated angle is equal to or larger than the predetermined angle, the conduction phase angle is set to the predetermined angle, and the DC component value of the developing bias corresponding to the difference between the calculated angle and the predetermined angle controls the image density formed on the recording material. , The image can be adjusted to the set density, and unnecessary noise and harmonics can be suppressed.

Further, the light quantity of the document illumination is controlled by the phase control of the AC power supply, and a predetermined quantity of the light quantity of the document illumination is expressed as a predetermined angle in the conduction phase angle, and the light quantity of the document illumination corresponding to the set image density is obtained. The conduction phase angle in the phase control is calculated, and if the calculated angle is equal to or smaller than a predetermined angle, the conduction phase angle is set to the calculated angle, and if the calculated angle is equal to or larger than the predetermined angle, the conduction phase angle is set to the predetermined angle. By controlling the image density formed on the recording material by the bias value supplied to the charging unit corresponding to the difference between the angle and the predetermined angle, the image can be adjusted to the set density, and unnecessary Noise and harmonics can be suppressed.

[Brief description of the drawings]

FIG. 1 is a control block diagram illustrating an image forming apparatus according to an embodiment;

FIG. 2 is a schematic configuration diagram illustrating an image forming apparatus according to the embodiment;

FIG. 3 is a structural diagram showing a document illumination lamp driving circuit according to the embodiment;

FIG. 4 is a flowchart illustrating control of the image forming apparatus according to the embodiment;

FIG. 5 is a graph showing a voltage waveform of a developing bias according to the embodiment.

FIG. 6 is a graph showing a voltage waveform during phase control according to the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 3 drive circuit 4 control circuit 5 CPU 6 memory 7 high-voltage power supply 9 charger 11 original illumination lamp 14 developing device 16 photosensitive drum 18 charger 19 zero-cross detection circuit 25 trigger pulse 27 zero-cross detection signal

Claims (3)

[Claims] An image bearing member is charged by charging means,
A latent image is formed on an image carrier by exposing an illuminated document image, and the latent image is developed by applying a developing bias to a developing unit, and the developed image is transferred to a recording material. When setting the image density of the image formed on the recording material, when the light amount of the original illumination is set to a predetermined amount or more, the image density is controlled by the light amount of the original illumination, and when the light amount of the original illumination is set to a predetermined amount or less. An image forming apparatus comprising: a light source for illuminating a document; and a control unit for controlling an image density by changing at least one of a DC component of a developing bias and a bias value supplied to a charging unit. 2. The amount of light of the original illumination is controlled by the phase control of an AC power supply, the predetermined amount of the amount of illumination of the original is expressed as a predetermined angle in a conduction phase angle, and the amount of light of the original illumination corresponding to the set image density is determined. Calculate the conduction phase angle in the phase control, and if the calculated angle is less than a predetermined angle, set the conduction phase angle to the calculated angle; if the calculated angle is more than the predetermined angle, set the conduction phase angle to the predetermined angle and calculate 2. The image forming apparatus according to claim 1, wherein an image density formed on a recording material is controlled by a DC component value of the developing bias corresponding to a difference between an angle and a predetermined angle. 3. The amount of light of the original illumination is controlled by phase control of an AC power supply, and the predetermined amount of the amount of illumination of the original is expressed as a predetermined angle in the conduction phase angle, and the amount of light of the original illumination corresponding to the set image density is determined. Calculate the conduction phase angle in the phase control, and if the calculated angle is less than a predetermined angle, set the conduction phase angle to the calculated angle; if the calculated angle is more than the predetermined angle, set the conduction phase angle to the predetermined angle and calculate 2. The image forming apparatus according to claim 1, wherein an image density formed on a recording material is controlled by a bias value supplied to the charging unit corresponding to a difference between an angle and a predetermined angle.