JP3184141B2 - Scanning optical device having jitter improving function and image forming apparatus using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning optical apparatus having a jitter improving function and an image forming apparatus using the same, and more particularly to an image forming apparatus using an electrophotographic printer, a digital copying machine, a plate making apparatus, and the like. The present invention relates to a scanning optical device having a jitter improving function in an image forming apparatus to be formed and an image forming apparatus using the same.

[0002]

2. Description of the Related Art In an image forming apparatus, such as an electrophotographic printer, a digital copying machine, and a plate making apparatus, in which a laser beam is optically written on a recording surface, a method of detecting a horizontal synchronizing signal of the laser beam uses In general, a method in which an analog waveform is detected by a synchronization sensor through a slit and converted into a square wave is used as a horizontal synchronization signal. In this detection method, the uneven rotation of the polygon mirror, the change in the light amount of the laser diode, etc.
The synchronization signal detected by the sensor is affected, and an image defect called jitter occurs.

FIG. 5 is a block diagram of a conventional scanning optical apparatus having a jitter improving function and an image forming apparatus using the same as disclosed in Japanese Patent Application Laid-Open No. 5-336330.

Referring to FIG. 5, this conventional example provides an image forming apparatus which includes a laser beam scanning means and a synchronizing signal generating means and which can accurately control the timing of writing an image even when a plurality of laser light amounts are used. .

This conventional example is an image forming apparatus for forming a color image by repeatedly charging, exposing, and developing a photoreceptor. A laser light amount detecting circuit 112 for detecting a light amount of a laser, A laser light quantity setting circuit 110 for setting a laser light quantity in accordance with the laser light quantity, and a laser light quantity control circuit 11 for controlling the laser light quantity so as to reach the set value.
1, a rotary polygon mirror 4 for performing main scanning by irradiating an image forming surface by repeatedly deflecting a laser beam by a constant angle;
A photodetector 8 for detecting a laser beam to be reached within a deflection range of the rotary polygon mirror 4 and to a region on the upper side of the image writing region to generate an analog signal, and output by the photodetector 8 A synchronous signal generating circuit 113 for changing a threshold voltage based on the analog signal g and the output of the laser light amount detecting circuit 112 or the laser light amount setting circuit 110 and controlling the timing of generating the write start position signal h; Generation can be prevented and jitter on an image due to a change in the amount of laser light can be eliminated.

[0006]

A first problem with the conventional scanning optical apparatus having the jitter improving function and the image forming apparatus using the same is that the circuit configuration is complicated.
That's what it means. The reason is that the threshold voltage is changed according to the change in the amount of laser light of the analog signal g output from the photodetector 8.

[0007] The second problem is that the entire jitter improving circuit is unstable and is easily affected by disturbance.
The reason is that an analog signal is used.

SUMMARY OF THE INVENTION An object of the present invention is to provide a scanning optical apparatus having a stable jitter improving function with a simple circuit configuration and an image forming apparatus using the same.

[0009]

Scanning optical device having a jitter improvement function of the present invention According to an aspect of the laser for the laser light intensity constant
Means for condensing laser light generated from a semiconductor laser having a light amount stabilizing circuit, a rotating polygon mirror rotating at a constant speed for deflecting the laser light, and the deflected laser light Means for imaging, a laser scanning optical unit consisting of a photodetector that detects the laser light to reach the region in the main scanning direction upstream from the image writing start position and outputs a sensor output signal, A synchronizing signal width counting circuit for counting the signal width of the sensor output signal with a clock and outputting it as the number of clocks; and a threshold for setting the sensor output signal.
Count the width of the synchronization pulse
Observe the number of clocks for a predetermined time at the time of initial setting, and calculate the average
Pseudo sync signal generation circuit that outputs a value as a pseudo sync signal
And a signal processing unit comprising:

[0010]

[0011]

Further, a scanning optical device having a jitter improving function according to the present invention comprises: a comparator for outputting a synchronization pulse obtained by pulsing the sensor output signal, which is an output of the photodetector, with a set threshold value; An oscillator that outputs a clock used to measure the width of the synchronization pulse, a gate circuit that gates the clock with the synchronization pulse and outputs a count clock, counts the clock of the count clock, and outputs the count as the number of clocks And a synchronization signal width counting circuit comprising a counter for performing the synchronization.

Further, in the scanning optical apparatus having the jitter improving function of the present invention, when the maximum value of the number of clocks of the synchronization pulse is Smax and the minimum value is Smin, (Smax + Smin) / 2
Is a pseudo-synchronous signal.

Further, the image forming apparatus of the present invention uses the scanning optical device as an exposure unit, and includes charging, developing, transferring, and fixing units.

[0015]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. Referring to FIG. 1, a scanning optical device having a jitter improving function according to this embodiment is a laser scanning optical unit 40.
And a signal processing unit 50.

In the laser scanning optical unit 40,
The laser light generated by the semiconductor laser 1
Is incident on the rotating polygon mirror 4 via the cylindrical lens 3 and is deflected by the rotating polygon mirror 4 rotating at a high speed at a constant speed. The deflected laser light is transmitted to the Fθ lens 5
The image is formed on the charged surface of the photosensitive drum 7 via the mirror 6 and the mirror 6. The spot of the laser light is repeatedly moved in the direction of arrow X by the rotation of the rotary polygon mirror 4 (main scanning), and at the same time, the photosensitive drum 7 is rotated in the direction of arrow Y (sub-scanning). The laser light that should reach the region on the photosensitive drum 7 that is on the upper side of the writing region, that is, the region that is upstream of the image writing start position in the main scanning direction, does not enter the mirror 6 but enters the photodetector 8. . When the laser beam enters, the photodetector 8 outputs a sensor output signal 9.

The signal processing section 50 counts the signal width of the sensor output signal 9 transmitted from the photodetector 8 of the laser scanning optical unit 40 with a clock and outputs the same as the number of clocks N. A center position detection circuit 20 for detecting the center of the sensor output signal 9 from the number of clocks N.

Referring to FIG. 2 showing a block diagram of the configuration of the synchronization signal width counting circuit 10 and FIG. 3 which is a signal waveform diagram, the synchronization signal width counting circuit 10 includes a sensor output signal 9 which is an output of the photodetector 8. , A comparator 11 that outputs a synchronization pulse 15 pulsed with a set threshold αV, an oscillator 12 that outputs a clock 16 used to measure the width of the synchronization pulse 15, and a synchronization pulse A gate circuit 13 gated by 15 and outputs a count clock 17, and a counter 14 that counts the count clock 17 and outputs the count as the number N of clocks.

The center position detection circuit 20 determines the number of synchronization pulses 1 based on the number of clocks N sent from the synchronization signal width counting circuit 10.
N at falling position of 5 (initial position of synchronization pulse 15)
The time corresponding to the position of / 2 clock is set to the sensor output signal 9
And outputs a synchronization signal 21 at the center position of. By scanning the photosensitive drum 7 based on an image signal transmitted from an external device (not shown) based on the synchronization signal 21, an image without jitter can be generated.

FIG. 4 is a block diagram showing a second embodiment of the present invention. Referring to FIG. 4, a scanning optical apparatus having a jitter improving function according to the second embodiment includes a laser scanning optical unit 40.
And a signal processing unit 60.

The laser scanning optical unit 40 has the same configuration as that described in the first embodiment, except that a laser light amount stabilizing circuit 70 for keeping the laser light amount constant with respect to the semiconductor laser 1 is added. Are different.

The signal processing section 60 comprises a synchronous signal width counting circuit 10 having the same function as in the first embodiment, and a pseudo synchronous signal generating circuit 30.

The pseudo synchronizing signal generation circuit 30 observes the number N of clocks of the synchronizing pulse for a predetermined time at the time of initialization, and outputs an average value thereof as a pseudo synchronizing signal 31. By scanning the photosensitive drum 7 based on an image signal transmitted from an external device (not shown) with reference to the pseudo synchronization signal 31, an image without jitter can be generated.

In the pseudo synchronizing signal generating circuit 30, when outputting the pseudo synchronizing signal 31, the average value of the number N of clocks of the synchronizing pulse 15 is used. When the minimum value is Smin, (Smax + Smin) / 2 may be used as the pseudo synchronization signal 31.

[0026]

As described above, the first effect of the present invention is that the circuit configuration is simple. The reason is that a circuit that counts the signal width of the sensor output signal output from the photodetector with a clock is employed.

The second effect is that the device is stable without being affected by disturbance. The reason is that a circuit for counting the signal width of the sensor output signal output from the photodetector with a clock, that is, a digitized signal is used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a synchronization signal width counting circuit in this embodiment.

FIG. 3 is a signal waveform diagram in this embodiment.

FIG. 4 is a block diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Condensing lens 3 Cylindrical lens 4 Rotating polygon mirror 5 Fθ lens 6 Mirror 7 Photoconductor drum 8 Photodetector 9 Sensor output signal 10 Synchronous signal width counting circuit 11 Comparator 12 Oscillator 13 Gate circuit 14 Counter 15 Synchronous pulse Reference Signs List 16 clock 17 counting clock 20 center position detection circuit 21 synchronization signal 30 pseudo synchronization signal generation circuit 31 pseudo synchronization signal 40 laser scanning optical unit 50 signal processing unit 60 signal processing unit 70 laser light amount stabilization circuit

Claims (4)

(57) [Claims] 1. A means for condensing laser light generated from a semiconductor laser having a laser light quantity stabilizing circuit for keeping the laser light quantity constant, a rotating polygon mirror rotating at a high speed at a constant speed for deflecting the laser light, and a deflecting means. A laser for forming an image of the laser beam thus formed, and a photodetector for detecting the laser beam to reach an area upstream of the image writing start position in the main scanning direction and outputting a sensor output signal. A scanning optical unit, a synchronization signal width counting circuit that counts the signal width of the sensor output signal with a clock and outputs the same as the number of clocks, and a synchronization pulse width obtained by pulsing the sensor output signal with a set threshold. A signal processing unit comprising a pseudo-synchronous signal generation circuit for observing the number of clocks counted by the clock for a predetermined time at the time of initial setting, and outputting an average value thereof as a pseudo-synchronous signal; Scanning optical device having a jitter improvement function, characterized in that to obtain. 2. A comparator for outputting a synchronization pulse obtained by pulsing the sensor output signal, which is an output of the photodetector, with a set threshold value, and a clock used for measuring the width of the synchronization pulse. An output oscillator, a gate circuit that gates the clock with the synchronization pulse to output a count clock, and a synchronization signal width counting circuit that includes a counter that counts the clock of the count clock and outputs it as the number of clocks. 2. The method according to claim 1, wherein
A scanning optical device having the jitter improving function as described above . 3. The maximum value of the number of clocks of the synchronizing pulse is
2. A scanning optical system having a jitter improving function according to claim 1, further comprising a pseudo-synchronous signal generating circuit, wherein Smax is the minimum value and Smin is the minimum value, and (Smax + Smin) / 2 is a pseudo-synchronous signal. apparatus. 4. An image forming apparatus according to claim 1, wherein said scanning optical device is used as an exposing means, and is provided with charging, developing, transferring and fixing means.