JPS6355708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser beam printer that scans a light beam to expose a photoreceptor to visualize a latent image formed electrically or magnetically, and particularly relates to a laser beam printer that scans a light beam to expose a photoreceptor and visualizes a latent image formed electrically or magnetically. The present invention relates to a laser beam printer that prevents this from occurring and obtains a desired image.

FIG. 1 is a schematic configuration diagram for explaining the principle of a laser beam printer. In the figure, a laser beam 15 generated from a laser generator 13 and turned on and off by a video signal 11 is irradiated onto a polygonal reflecting mirror 17 . The reflected laser beam is then focused by an f/theta lens 19, and then forms a spot image on the photosensitive surface 23 of the photosensitive drum 21. Here, beam scanning in the a direction (main scanning direction) is performed by rotating the polygonal reflecting mirror 17 in the b direction. Further, by rotating the photoreceptor drum 21 in the direction c, sub-scanning is performed in a direction perpendicular to the main scanning direction (direction a).

In this manner, a latent image is formed on the photosensitive surface 23 exposed by the laser beam 15 in response to the video signal 11. This latent image is developed by a visualization means (described later), and the transfer material 25 advances in the direction d according to the rotation of the photoreceptor drum 21.
An output image is obtained at .

FIG. 2 is a block diagram of a conventional laser beam printer. Since this is an application of the principle shown in FIG. 1, common elements are given the same symbols. Note that this printer employs an electrophotographic process known as the Carlson method.

In FIG. 2, the video signal 11 is based on the information to be printed stored in the page memory 31.
As a result, an intermittent laser beam 15 is generated from the laser generator 13. The intensity of this generated laser beam 15 is controlled by a laser drive signal 35 from a laser current driver 33. The laser beam 15 is reflected by the polygonal reflecting mirror 17, focused by the θ lens 19, reflected by the optical path direction changing mirror 37, and then directed to the photosensitive drum 2.
1 to a photosensitive surface 23. Note that the main scanning and sub-scanning are the same as those described with respect to FIG.

The photosensitive surface 23 of the photosensitive drum 21 rotating in the direction c is first uniformly charged to several thousand volts by a primary charger 41 by corona discharge. In this state, when the laser beam 15, which is controlled on and off by the video signal 11, is irradiated, a static elimination operation is performed.
An electrostatic latent image is formed. The photosensitive surface 23 on which the electrostatic latent image is formed in this manner has a partially changed electrostatic potential.

In the area of the electrostatic latent image formed on the photosensitive surface 23,
Toner charged to several hundred volts is applied from the developing device 43 and developed. Then, the image with the toner attached is transferred by the transfer charger 45 to the transfer material 25 moving in the d direction. Therefore, the store information in the page memory 31 is recorded on the transfer material 25 made of plain paper, for example.

After the transfer, the remaining toner is removed by a cleaning blade 47, and the remaining electrostatic potential is erased (however, the means for doing so is not shown) to prepare for the next electrostatic latent image formation.

In such conventional laser beam printers,
The amount of light of the laser beam 15 that irradiates the photosensitive surface 23 of the photosensitive drum 21 differs significantly depending on the location on the drum 21 due to factors such as vibration of the device. In particular, vibrations generated from the drive system of the photoreceptor drum 21 may distort the optical path, or the photoreceptor drum 21 may slightly vibrate in the rotational direction due to changes in the torque of the drive transmission system. Therefore, a shift in the relative position between the beam and the photoreceptor occurs. FIG. 3 shows characteristics based on such relative positional deviation. Here, a curve 51 shows the characteristics of the relative position L vs. the light intensity I of the beam, a curve 53 shows the characteristics of the light intensity I vs. the potential V of the photoreceptor, and a curve 55 shows the characteristics of the relative position vs. the potential V. The dotted line 57 is the average of the characteristics shown by the curve 55. Here, the latent image intensity represented by the magnitude of the potential V takes a maximum value S1 and a minimum value S2, and a latent image intensity difference ΔS is generated between them. In other words, there is an extremely large deviation in the latent image intensity depending on the position. Further, the potential V represented by this curve 55 oscillates at potentials corresponding to white and black in terms of image density. Therefore, if the beam is exposed as it is, scanning traces will occur on the image, and the transfer material 25
The disadvantage of recording in this way is that it looks bad.
Therefore, especially in high-speed printers, it is possible to obtain good-looking image output without scanning traces, and to produce so-called positive images.
There was a demand for a laser beam printer that would output a uniformly white image on the area hit by light in the case of a system, and uniformly black in the area hit by the light in the case of a negative system. .

The purpose of the present invention is to meet such demands,
Even if there is a relative positional shift between the beam and the photoreceptor,
The object of the present invention is to realize a laser beam printer that is not affected by this and can obtain images without scanning traces. That is, the present invention provides a laser beam printer that controls the light intensity of a laser beam before printing, including a potential detecting means for detecting the surface potential of a photoreceptor exposed to the laser beam, and a surface potential detected by the potential detecting means. a low-pass filter for averaging potential signals; and a relative relationship in the sub-scanning direction that periodically occurs between the laser beam averaged by the low-pass filter and the photoreceptor. means for Fourier-transforming a potential signal corresponding to a target position shift; and a means for storing a component obtained by the Fourier transform, and a potential averaged by the low-pass filter according to the stored component. means for reproducing a waveform according to the signal; and a control means for controlling the light intensity of the laser beam based on the reproduced waveform and a waveform with the amplitude and phase of the waveform changed; The photoconductor is exposed to a laser beam whose light intensity is controlled based on the reproduced waveform, the difference between the maximum value and the minimum value of the surface potential of the exposed photoconductor is detected, and the difference between the maximum value and the minimum value is detected. The amplitude and phase of the reproduced waveform are controlled until the amplitude and phase of the reproduced waveform are minimized, and when recording print information, the light intensity of the laser beam is controlled based on the waveform whose amplitude and phase have been controlled. It is.

The present invention will be explained in detail below based on the drawings.

FIG. 4 is a configuration diagram of an embodiment of the present invention. The difference from FIG. 2 is that a potential sensor 6 is used as the potential detection means.
1 and a controller 65 are provided. For example, the potential sensor 6 detects the electrostatic potential of a latent image formed in an area (non-image area) of the photosensitive surface 23 where no image latent image is formed according to store information in the page memory 31.
1 to detect. In response to the detection signal 63, a laser control signal 67 is generated from the controller 65. This control signal 67 causes the laser current driver 33 to
The laser drive signal 35 from is controlled, and the light intensity of the laser beam 15 changes accordingly.

FIG. 5 is a block diagram showing a specific example of the controller 65 shown in FIG. In the figure, a detection signal 63 from a potential sensor 61 is averaged by a low-pass waveform generator 81, resulting in a characteristic indicated by a dotted line 57 shown in FIG. When the changeover switch 83 provided on the output side of the wave generator 81 is at the contact point p, the wave output signal 85 is introduced into a fast Fourier transform (hereinafter referred to as FFT) calculator 87. Here, assume that it is Fourier transformed and now has two components. Below, a means for storing the components obtained by the Fourier transform and reproducing a waveform corresponding to the potential signal averaged by the low-pass filter according to the stored components will be explained. . The components obtained by the Fourier transform are both the frequency f ₁ phase φ ₁ and the frequency ₂ and phase φ ₂ components, and these pieces of information are stored in the table memory 89. Voltage controlled oscillators (hereinafter referred to as VCO) 91 and 93 oscillate to output sine wave signals 95 and 97 of frequencies ₁ and ₂ , respectively, based on frequency information ( ₁ and ₂ ) stored in table memory 89. do. These signals 95 and 97 are transmitted to the phase shifter 10, respectively.
1,103 based on the phase information (φ ₁ and φ ₂ ) stored in the table memory 89, the signal is synthesized by the signal synthesizer 105, and then the signal is synthesized by the low-pass filter. A waveform corresponding to the averaged potential signal is reproduced. A control means for controlling the light intensity of the laser beam based on this reproduced waveform and a waveform obtained by changing the amplitude and phase of the waveform will be explained. The synthesized signal 107 synthesized by the signal synthesizer 105 is phase-shifted by the variable phase shifter 109 based on the phase information of the wave output signal 85 when the switch 83 is at the contact point q. Further, based on the amplitude information when the switch 83 is at the contact point r, the composite signal 107 is amplified in the variable gain amplifier 111, and then the laser control signal 67 is
The current is supplied to the laser current driver 33.
According to the control signal 67 thus formed, the laser drive signal 35 is controlled and the light intensity of the laser beam 15 is changed.

FIG. 6 is a flowchart for explaining the operation sequence of FIG. 5. Please refer to FIGS. 3 to 6. First, the laser drive signal 35 is set to an initial predetermined current value in the laser current driver 33 (block 131). Such an initial laser drive signal 35
As a result, a laser beam 15 is generated, thereby performing a static elimination operation. Next, the changeover switch 83 is connected to the contact p, and the required time wave output signal 85 is introduced into the FFT calculator 87 to perform FFT calculation (block 133). Then, the frequency and phase information obtained by the FFT calculation are stored in the table memory 89 (block 135). Both VCOs 91 and 93 are caused to oscillate according to the frequency information, and both phase shifters 101 and 93 are caused to oscillate according to the phase information.
The phase is shifted at 103 and phase matching is performed. After that,
Both oscillation outputs are combined and averaged by a low-pass waveformer to reproduce a waveform corresponding to the potential signal. This reproduced composite signal 107 is sent to the synthesizer 10
5 (block 137). Note that this composite signal 107 does not change until the next FFT calculation.

Further, the composite signal 107 is phase-shifted by the variable phase shifter 109 by a predetermined phase shift amount φ109. Further, the composite signal 107 is amplified by the variable amplifier 111 to become the laser control signal 67 according to a predetermined gain G111 that is also set in advance.

Below, a photoreceptor is exposed to a laser beam whose light intensity is controlled based on the reproduced waveform, and the reproduced waveform is formed until the difference between the maximum value and the minimum value of the surface potential of the exposed photoreceptor becomes the minimum. To explain the means for controlling the amplitude and phase of the laser beam, first, the light intensity of the laser beam 15 is regulated based on the reproduced waveform, and the latent image intensity is measured by the potential sensor 61.
Then, the latent image intensity difference ΔS is determined from the maximum value S1 and the minimum value S2 (block 139). It is determined whether this intensity difference ΔS is the minimum (block 141). If negative, the changeover switch 83 is connected to the contact q to change the phase shift amount φ109 of the variable phase shifter 109, thereby shifting the phase of the composite signal 107 (block 143). Then, the process returns to block 139 and repeats this loop until the intensity difference ΔS is minimized.

When the strength difference ΔS becomes the minimum, the changeover switch 83
Connect to contact r. Therefore, variable phase shifter 10
A phase shift amount φ109 of 9 is defined.

Therefore, the gain G111 of the variable gain amplifier 111 is now defined by the wave output signal 85. Thereby, the static elimination operation is performed in accordance with the laser control signal 67 obtained by amplifying the composite signal 107. A latent image intensity difference ΔS is determined by the potential sensor 61 (block 145). It is determined whether this intensity difference ΔS is the minimum (block 147). If negative,
By changing the gain G111 of the variable gain amplifier 111, the amplitude of the laser control signal 53 is changed (block 149). The process then returns to block 145. This loop operation is repeated until the intensity difference ΔS becomes the minimum. Since the gain G111 is defined when the intensity difference ΔS is minimized, the current value of the laser drive signal 35 is defined accordingly. That is, the light intensity of the laser beam is controlled based on a waveform whose amplitude and phase are controlled. When recording print information, the light intensity of the laser beam is controlled based on the waveform whose amplitude and phase are controlled, and image formation is performed by controlling the laser beam on and off using the video signal 11 (block 149).

By the way, when reading the latent image intensity difference ΔS (blocks 139 and 145), the laser is driven so that the average value of the maximum value S1 and minimum value S2 gives the latent image intensity corresponding to the halftone of the output image. It is preferable to set the signal 35 to determine the intensity of the laser beam 15. If so set, when the intensity difference ΔS is determined to be the minimum (blocks 141 and 149), the laser beam is turned on in that case,
Off is convenient because it corresponds to the black and white of the image.

FIG. 7 is a characteristic diagram of the relative position L between the laser and the photoreceptor in the embodiment of the present invention shown in FIG. Here, the curve 161 is the characteristic of the relative position L versus the light intensity I, the curve 163 is the characteristic of the light intensity I versus the electrostatic potential V of the photoreceptor, and the curve 165 is the characteristic of the relative position L versus the potential V. As can be seen from the characteristics of the curve 165, the latent image intensity is approximately constant and does not vary between white and black levels. This is done by detecting the potential V with the potential sensor 61, controlling the laser drive current with the controller 65, and changing the intensity of the laser beam 15 sinusoidally (indicated by a dotted line 167), that is, sin(2πL/
T) is modulated by an amount proportional to T). Here, T is the period.

A dotted line 169 is a characteristic showing a change in the potential V when no writing is performed by the laser beam 15 (indicated by a dashed-dotted line 171).
In other words, there is a sufficient difference in latent image strength,
This is a sufficient difference in intensity to separate white and black. Thereby, even if an image is output by scanning with the laser beam 15, no trace of scanning remains as an image.

Note that the phase shifters 101, 103, and 109 in FIG. 5 may be of any type as long as they generate phase-shifted output signals as a result. For example, a phase lock loop circuit may be used to lock the phase by a phase amount.

By the way, the timing for performing the operation shown in FIG. 5 will be explained. This is usually done after the laser beam printer is powered on and before printing.
If this was done by detecting the intensity of the latent image to be transferred to the transfer material 25, there is a possibility that the transfer material would be wasted. Therefore, a laser intensity setting operation is performed in the area of the photoreceptor that is not transferred and before the transfer is performed. However, according to experiments, the relative positional vibration pattern between the beam and the photoreceptor was approximately periodic, and the pattern did not change over a short period of time. Therefore,
The operations of blocks 131 to 135 in FIG. 6 do not need to be performed every time an image is output. The operations to be performed each time an image is output may be those in blocks 137 to 149. It can be said that the operations of blocks 137 to 147 are most efficiently performed using the image output interval. Note that when used in a so-called multi-output specific normal state, the variable gain amplifier 1 shown in FIG.
The variable gain control operation in step 11 may be omitted.

Furthermore, although the above description has been made regarding a photoreceptor on which a latent image is electrically formed, the photoreceptor may also be a photoreceptor whose magnetism changes when raised to a temperature equal to or higher than the Curie temperature by the laser beam 15. In that case, it is necessary to replace the potential sensor 61 with a magnetic sensor.

According to the present invention, in a laser beam printer that controls the light intensity of a laser beam before printing, there is provided a potential detecting means for detecting a surface potential of a photoreceptor exposed to the laser beam, and a potential detected by the potential detecting means. a low-pass filter for averaging the potential signals, and a sub-scanning direction filter that periodically occurs between the laser beam averaged by the low-pass filter and the photoreceptor. means for Fourier transforming a potential signal according to a relative positional shift, storing components obtained by the Fourier transform, and averaging the components by the low-pass filter according to the stored components; It has a means for reproducing a waveform according to the potential signal, and a control means for controlling the light intensity of the laser beam based on the reproduced waveform and a waveform obtained by changing the amplitude and phase of the waveform, the control means The photoreceptor is exposed to a laser beam whose light intensity is controlled based on the reproduced waveform, the difference between the maximum and minimum values of the surface potential of the exposed photoreceptor is detected, and the difference between the maximum and minimum values is detected. By controlling the amplitude and phase of the reproduced waveform until the difference is minimized, and controlling the light intensity of the laser beam based on the waveform whose amplitude and phase have been controlled when recording print information, the laser beam It is possible to erase scanning traces due to relative positional deviation in the sub-scanning direction that periodically occurs between the photoreceptor and the photoreceptor, thereby preventing deterioration of image quality and obtaining a good image.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of a laser beam printer, Figure 2
The figure is a configuration diagram of a conventional laser beam printer.
The figure is a characteristic diagram based on the relative positional deviation according to the configuration shown in FIG. 2, FIG. 4 is a configuration diagram showing an embodiment of the laser beam printer according to the present invention, and FIG. 5 is a detailed block diagram of a part of FIG. 4. 6 is a flowchart showing the operation of FIG. 5, and FIG. 7 is a characteristic diagram based on relative positional deviation due to the configuration of FIG. 4. 11...Video signal, 13...Laser generator,
17... Polygonal reflecting mirror, 19... f/θ lens,
21...Photosensitive drum, 25...Transfer material, 31...
...Page memory, 33...Laser current driver, 61
... Potential sensor, 65 ... Controller, 87 ...
FFT calculator, 89...Table memory, 101,
103, 109...phase shifter, 111...variable gain amplifier.

Claims (1)

[Scope of Claims] 1. A laser beam printer that controls the light intensity of a laser beam before printing, comprising: a potential detecting means for detecting a surface potential of a photoreceptor exposed by the laser beam; and detection by the potential detecting means. a low-pass filter for averaging the potential signals; and a sub-scanning direction that periodically occurs between the laser beam averaged by the low-pass filter and the photoreceptor. means for Fourier-transforming a potential signal according to a relative positional shift of the component; and a means for storing components obtained by the Fourier transform, and averaging the components by the low-pass filter according to the stored components. means for reproducing a waveform corresponding to the potential signal; and a control means for controlling the light intensity of the laser beam based on the reproduced waveform and a waveform with the amplitude and phase of the waveform changed; exposes the photoreceptor with a laser beam whose light intensity is controlled based on the reproduced waveform, detects the difference between the maximum value and the minimum value of the surface potential of the exposed photoreceptor, and detects the difference between the maximum value and the minimum value. The amplitude and phase of the reproduced waveform are controlled until the difference in the amplitude and phase is minimized, and when recording print information, the light intensity of the laser beam is controlled based on the waveform whose amplitude and phase have been controlled. laser beam printer.