JP3441744B2 - Electrostatic latent image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic latent image forming apparatus used in a laser printer, a digital copying machine or the like, and is particularly suitable for use in a color copying machine. The present invention relates to a device that generates an element drive signal that performs gradation expression by controlling a width and a pulse intensity.

[0002]

2. Description of the Related Art Conventionally, a laser beam is scanned and this laser beam is scanned.
An electrostatic latent image is formed on the photoconductor by the blinking of the beam,
Laser beam printer (LBP) for recording desired images
A digital copying machine that records image information based on image information obtained by scanning and reading a document is widely used. An example of a schematic configuration diagram of a scanning optical system used in such an apparatus will be described with reference to FIG. 9. A laser driver 1 oscillates a semiconductor laser 2 which is one of light emitting elements to emit laser light. Then, the laser light is made into substantially parallel light by the collimator lens 3. The substantially parallel light is reflected by the rotary polygon mirror 5 that rotates at a constant angular velocity in the arrow A direction, and scans on the photosensitive drum 9 (photoconductor) in the arrow B direction. The imaging lens groups 6a, 6b, 6c form an image of the substantially parallel light on the photosensitive drum 9 and the slit 7a, and the scanning speed of the laser light scanning the photosensitive drum 9 is constant. Therefore, it has the function of speed adjustment. The laser light incident on the slit 7a is guided to the photodetector 7c through the condenser lens 7b and is sent to the control unit 10 as a horizontal synchronizing signal. The slit 7a is an opening whose longitudinal direction is perpendicular to the scanning direction, and is arranged at a position optically equivalent to the surface of the photosensitive drum 9. Around the photosensitive drum 9, there are provided a developing device, a primary charging device, a transfer charging device, a fixing device, a cleaner and the like, which are not shown, and the latent image formed on the surface of the photosensitive drum 9 is well known. It is visualized by an electrophotographic process and transferred to a transfer material.

In order to express the image density gradation in such an apparatus, it is general to control the pulse width of the laser drive signal for oscillating the semiconductor laser in correspondence with the image density. That is, the image density for one pixel in the main scanning direction is decomposed into gradation levels, and the pulse width of the laser drive signal is changed corresponding to the decomposed gradation levels. The change in the pulse width is caused by the laser beam
By scanning the upper part at a constant speed, it appears as a difference in the size of the latent image area formed by one pulse, so that the image density can be reproduced.

[0004]

However, in the case of the above-mentioned conventional example, when trying to express the low-density region, the laser drive signal width becomes short, and the beam spot is included in the drive signal and the emitted laser light. Has a finite width, there is a problem that the drive signal changes before the emission pulse reaches the peak intensity of the beam spot, and the density cannot be expressed correctly.

This phenomenon will be described with reference to the drawings. Figure 10
Shows the pulse waveform of the conventional laser drive signal when the density is equally divided into 8 gradations, where the laser drive signal is represented by the current value i on the vertical axis and the time is represented on the horizontal axis. In FIG. 11, the laser light intensity when the semiconductor laser is controlled by the laser drive signal shown in FIG.
Is represented on the horizontal axis, and the pulses of the waveforms a and b in FIG. 10 correspond to the laser light intensities a and b in FIG. Note that in FIG. 11, the rise time of the laser light intensity is shown so that the pulse width and the laser light intensity can be easily compared.

The time width of the laser light intensity also changes depending on the pulse width of the laser drive signal. Especially when the pulse widths of the waveforms a, b, and c are the emission pulses, the emission pulse reaches the peak intensity of the beam spot due to the reason described above. Since the pulse signal ends before it reaches the limit, the emission intensity does not reach the steady intensity, and only a low level occurs.

In the figure, V indicates a threshold level at which an image is visualized by development after the photosensitive drum is irradiated with laser light and converted into a potential, and development is performed at a level above the level. Is done. Therefore, the pulse widths a, b
In the case of, the phenomenon that the image density was not developed due to no development was occurred.

Attempts have been made to reduce the spot diameter in the main scanning direction in order to reduce this phenomenon as much as possible. However, there is a limit to the miniaturization of the spot diameter, and extreme miniaturization reduces the depth at the image plane. It is not a good idea because it not only reduces the cost, but also increases production costs and requires advanced adjustment.

Therefore, it is an object of the present invention to provide an electrostatic latent image forming apparatus which does not require miniaturization of a spot diameter in reproducing a low density area and does not require a high degree of adjustment.

[0010]

The present invention has been made in view of the above circumstances, and uniformly charges the surface of a photoconductor and irradiates the surface of the photoconductor with light emitted from a light emitting element. Thus, in the electrostatic latent image forming apparatus that forms the electrostatic latent image, the differential waveform of the element driving signal is self-superposed on the element driving signal applied to the light emitting element.

[0011]

For example, in the differential waveform of the element drive signal, the component having the same polarity as the element drive signal is directly used as the self-superimposing component, and the component having the different polarity from the element drive signal is added to the polarity. Is inverted to obtain a self-superimposed component.

Further, there is a judging circuit for judging whether or not the differential waveform is self-superposed on the basis of the signal width of the element driving signal. For example, the differential waveform of the element drive signal
Then, only the component of the same polarity as the element drive signal is the self-superposition component
And

[0014]

According to the above structure, the time required to reach the peak intensity of the beam spot is shortened by self-superimposing the differential waveform of the element driving signal on the element driving signal applied to the light emitting element.

[0015]

EXAMPLE 1 Example 1 of the present invention is shown in FIG.
As shown in FIG. FIG. 1A shows a pulse shape of a laser drive signal given to a semiconductor laser used in the present invention,
(b) is the waveform extracted by deriving the derivative of the waveform of (a) and then rectifying only the positive component, and (c) is the waveform obtained with (a).
The waveform of (b) is superimposed. Used in the present invention
The waveform in (c) is such that the signal strength at the rising edge of the pulse increases.

FIG. 2 shows a block diagram of a circuit for generating the waveform of FIG. After generating a pulse signal according to the image signal in the pulse generation circuit, make a differential waveform of the pulse in the differentiation circuit, take out the positive component by the rectification circuit,
By adding the differential component after rectification to the initial pulse waveform by the adder circuit, a pulse waveform having a high rising signal strength is formed.

The details of the pulse waveform by this circuit are shown in FIG. 3A is a pulse waveform of the laser drive signal from the pulse generating circuit, FIG. 3B is a differential waveform of the pulse signal, and FIG. 3C is a differential component of the differential waveform extracted by the rectifying circuit. And (d) is the drive pulse signal
It is the result of superimposing the differential waveform of (a) and the positive component by the adder.

FIG. 4 shows a waveform in which the pulse width of such a drive signal is changed stepwise, and FIG. 5 shows the laser light intensity emitted from the semiconductor laser. Even when the pulse width of the drive signal is short, the laser light intensity can be raised to the same level as when the pulse width of the drive signal is long.

<Second Embodiment> A second embodiment will be described with reference to FIG. 6 (a) and 6 (b) are shown in FIG. 3 of the first embodiment.
Although the signals are the same as those in (a) and (b), of the superimposed differential waveforms, the component with the same polarity as the laser drive signal is the superimposed component as it is, and the component with different polarity is inverted to form the superimposed component.
What makes these two superimposed components into one superimposed waveform
(C). This causes the rise of the laser drive signal,
It is possible to obtain the laser drive signal that is large at both the falling edges. By using such a laser drive signal, the rise and fall times of laser light can be made accurate.

<Third Embodiment> A third embodiment will be described with reference to FIG. 7A shows the pulse waveform of the laser driving signal, which is the same as FIG. 3A of the first embodiment, but the differential waveform of FIG. 7B is only when the pulse width of the laser driving signal is short. It is being output. (c) is a product obtained by rectifying the differential waveform and extracting only the positive component, and (d) is the result of superimposing (a) and (c). FIG. 8 is a block diagram of an electric circuit for performing the above-described processing, in which a determination circuit located after the image signal detects the image signal pulse width and passes through a circuit for time differentiation, rectification and addition below a certain level. , It is possible to selectively add differential waveforms by not passing through these circuits when the level is above a certain level. By using this circuit, the differential waveform is added only to the short pulse width,
It is possible to remarkably improve the density level only in the low density region.

In the first, second, and third embodiments described above, the semiconductor laser was used as the light emitting element, but the light emitting element is not limited to this element, and a light emitting diode or the like may be used.

[0022]

According to the present invention, it is not necessary to miniaturize the spot diameter of the light emitting element by an inexpensive measure such as adding an electric circuit such as a differential waveform generating circuit and a rectifying circuit to the conventional structure, and it is possible to reduce the spot diameter. It is possible to provide an electrostatic latent image forming device capable of faithfully reproducing the density region.

[Brief description of drawings]

FIG. 1 is a configuration waveform diagram of a laser drive signal according to a first embodiment.

FIG. 2 is a block diagram of a laser drive signal generation circuit according to the first embodiment.

FIG. 3 is a detailed diagram of a constituent waveform of a laser drive signal according to the first embodiment.

FIG. 4 is a laser drive signal diagram for various pulse widths according to the first embodiment.

FIG. 5 is a laser beam intensity diagram for various pulse width laser drive signals according to the first embodiment.

FIG. 6 is a diagram showing a detailed view of constituent waveforms of a laser drive signal according to a second embodiment.

FIG. 7 is a diagram showing a detailed diagram of a constituent waveform of a laser drive signal according to a third embodiment.

FIG. 8 is a block diagram of a laser drive signal generation circuit according to a third embodiment.

FIG. 9 is a schematic view of a scanning optical system showing a conventional technique.

FIG. 10 is a laser drive signal diagram for various pulse widths according to the related art.

FIG. 11 is a laser light intensity diagram for laser drive signals of various pulse widths according to the related art.

[Explanation of symbols]

2 Light emitting device (semiconductor laser) 9 Photoconductor (photosensitive drum) R element light (laser light)

Claims (3)

(57) [Claims] 1. A photosensitive member having a uniformly charged surface,
By irradiating the surface with light emitted from the light emitting element,
Electrostatic latent image forming apparatus for forming an electrostatic latent imageAnd before
The element drive signal is applied to the element drive signal applied to the light emitting element.
Electrostatic latent image forming device for self-superimposing differential waveform of motion signalTo
AndOf the differential waveform of the element drive signal, the same as the element drive signal
The component of the same polarity is directly used as the self-superimposing component,
In addition to the components,
In other words, the polarity is inverted to form a self-superimposed component, An electrostatic latent image forming device characterized by the above. 2. The surface of the photoconductor is uniformly charged,
By irradiating the surface with light emitted from the light emitting element,
And an electrostatic latent image forming device for forming an electrostatic latent image,
The element drive signal is applied to the element drive signal applied to the light emitting element.
In an electrostatic latent image forming device that self-superimposes a differential waveform of a motion signal
And The differential waveform is self-weighted according to the signal width of the element drive signal.
Has a judgment circuit for judging whether or not to fold it, An electrostatic latent image forming device characterized by the above. 3. Of the differential waveforms of the element drive signal,
Only the component of the same polarity as the slave drive signal is the self-superposition component
The The electrostatic latent image forming device according to claim 2, wherein.