JPH11245445A - Laser driver, driving method and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the image quality of an electrophotographic apparatus where the gradation is represented in units of dot. SOLUTION: A drive current being fed from a current supply means 14 to a laser emitting means 12 is modulated by a current modulating means 17 according to a control signal being fed externally to a signal input means 18 in order to form an image where the gradation is represented in units of dot. When a laser beam is emitted while being modulated according to the control signal, emission intensity is varied at a specified period by an output varying means 20 such that dots of same size are not arranged at a fixed part thus enhancing the image quality.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser driving method and apparatus for emitting a laser beam modulated according to a control signal to a laser emitting means, and a laser driving apparatus for emitting a laser beam by the laser driving method. An image forming apparatus used.

[0002]

2. Description of the Related Art Conventionally, a laser driving device is frequently used as a scanning optical system in an image forming apparatus such as a laser printer. Such a laser driving device includes, for example, a semiconductor laser as a laser emitting unit, and supplies a driving current to the semiconductor laser to emit a corresponding amount of laser beam.

In an image forming apparatus using such a laser driving device, a driving current supplied to the semiconductor laser by the laser driving device is controlled in accordance with image data, and a polygon rotating a laser beam controlled in this manner is rotated. A deflection scan is performed in the main scanning direction by a mirror or the like. Further, the photosensitive drum as the latent image holding means is rotated to move the peripheral surface in the sub-scanning direction,
The peripheral surface of the photosensitive drum that moves in the sub-scanning direction is charged by a charging charger.

The charged, rotating photosensitive drum rotating in the sub-scanning direction is exposed and scanned with a laser beam deflected and scanned to form an electrostatic latent image, and the electrostatic latent image is formed by a latent image developing means. The toner is developed with a certain developing device. The toner on the peripheral surface of the photosensitive drum developed in this way is transferred to a recording medium by a transfer charger as a toner transfer unit, and the toner transferred to the recording medium is fixed by a fixing device as a toner fixing unit.

In the above-described image forming apparatus, since a print image is formed by a large number of dots arranged in a matrix, a gradation image can be formed even by binary dots by using a dither method or the like. However, since the resolution of a print image is reduced by such a method, there is an image forming apparatus which forms a gradation image with dots being multi-valued at present.

In such an image forming apparatus, for example, the drive time supplied to the semiconductor laser is modulated by PWM (Pulse Width Modulation) in accordance with image data, so that the emission time of the semiconductor laser is varied for each dot. . In this case, since each of a large number of dots forming the print image is formed in a size individually corresponding to the image density,
It is possible to form a high-resolution image toned in dot units.

[0007]

In the above-described image forming apparatus, the drive current supplied to the semiconductor laser is PWM-modulated in accordance with the image data, so that a high-resolution image toned in dot units is obtained. Can be formed.

In such an image forming apparatus, since the image density of the image data and the dot size correspond one to one, dots of the same size are arranged in a portion where the density of the print image is constant. Become. However, when dots of the same size are arranged in this way, for example, moiré may occur and the quality of a printed image may be degraded. Similarly, in the portion where the density of the print image changes sequentially, dots whose size changes sequentially are arranged, which may also cause the quality of the print image to deteriorate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has a laser driving method and apparatus capable of forming an image forming apparatus with a high-quality image toned in dot units. It is an object of the present invention to provide an image forming apparatus capable of forming a gradation image with high quality.

[0010]

According to a first aspect of the present invention, there is provided a laser driving method for modulating a laser beam emitted from a laser emitting means in accordance with a control signal input externally. Thus, the emission intensity of the modulated laser beam emitted from the laser emitting means is changed at a predetermined cycle.

Therefore, when the laser driving method of the present invention is applied to an electrophotographic image forming apparatus for forming a gradation image in dot units, dots of the same size are arranged in a portion where the density of a printed image is constant. In addition, there is no case where dots whose sizes are sequentially changed are arranged in portions where the density of the print image is sequentially changed.

According to a second aspect of the present invention, there is provided a laser driving method.
When a driving current is supplied from a current supply unit to a laser emitting unit to emit a corresponding amount of laser beam, a driving current supplied from the current supplying unit to the laser emitting unit in response to an externally input control signal In the laser driving method, wherein the driving current supplied from the current supply means to the laser emission means is changed at a predetermined cycle.

Therefore, when the laser driving method of the present invention is used in an electrophotographic image forming apparatus for forming a gradation image in dot units, dots of the same size are arranged in a portion where the density of a printed image is constant. In addition, there is no case where dots whose sizes are sequentially changed are arranged in portions where the density of the print image is sequentially changed.

According to a third aspect of the present invention, there is provided a laser driving method comprising:
When a drive current is supplied from the current supply unit to the laser emitting unit to emit a corresponding amount of laser beam, the amount of the laser beam is monitored by the laser monitor unit, and the corresponding voltage is temporarily held in the voltage holding unit, A drive current corresponding to the holding voltage of the temporary holding is generated by the current supply unit and supplied to the laser emission unit, and the drive current supplied in this manner is modulated according to a control signal input from the outside. In the above laser driving method, a dummy voltage changing at a predetermined cycle is applied to the voltage holding means.

Therefore, when the laser driving method of the present invention is used in an electrophotographic image forming apparatus for forming a gradation image in dot units, dots of the same size are arranged in a portion where the density of a printed image is constant. In addition, there is no case where dots whose sizes are sequentially changed are arranged in portions where the density of the print image is sequentially changed.

According to a fourth aspect of the present invention, there is provided a laser driving method comprising:
When a drive current is supplied from a current supply unit to a laser emitting unit to emit a laser beam of a corresponding light amount, the laser beam is monitored by a laser monitor unit and a current signal corresponding to the light amount is output. A laser driving method in which a corresponding drive current is generated by the current supply means and supplied to the laser emission means, and the drive current supplied in this manner is modulated according to a control signal input externally. Thus, a dummy current that changes at a predetermined cycle is superimposed on a current signal output from the laser monitoring unit to the current supply unit.

Therefore, when the laser driving method of the present invention is used in an electrophotographic image forming apparatus for forming a gradation image in dot units, dots of the same size are arranged in a portion where the density of a printed image is constant. In addition, there is no case where dots whose sizes are sequentially changed are arranged in portions where the density of the print image is sequentially changed.

According to a fifth aspect of the present invention, there is provided a laser driving device comprising:
A laser emitting unit that emits a laser beam in response to the supply of the driving current, a current supplying unit that generates a predetermined driving current and supplies the laser emitting unit, and a control signal of the laser emitting unit is externally input. Signal input means, current modulation means for modulating a drive current supplied to the laser emission means by the current supply means in response to a control signal externally input to the signal input means, and modulated by the current modulation means. Output varying means for changing the light emission intensity of the laser beam emitted by the laser emitting means at a predetermined cycle in accordance with the drive current.

Therefore, in the laser driving apparatus of the present invention, the driving current supplied to the laser emitting means by the current supplying means is modulated by the current modulating means in accordance with the control signal externally inputted to the signal input means. The laser beam emitted from the laser emitting means is modulated according to the control signal. Therefore, when this laser driving device is used in an electrophotographic image forming apparatus that forms a gradation image in dot units, a high-resolution image in which gradation is performed in dot units is formed. As described above, when the laser driving device emits the laser beam modulated in response to the control signal to the laser emitting unit, the emission intensity of the laser beam is changed at a predetermined cycle by the output varying unit. For this reason, when this laser drive device is used in an image forming apparatus, dots of the same size are not arranged in a portion where the density of the print image is constant, and the size is sequentially changed in a portion where the density of the print image changes sequentially. The changed dots are not arranged.

According to a sixth aspect of the present invention, there is provided a laser driving device.
A laser emitting unit that emits a laser beam in response to the supply of the driving current, a current supplying unit that generates a predetermined driving current and supplies the laser emitting unit, and a control signal of the laser emitting unit is externally input. Signal input means, current modulation means for modulating a drive current supplied to the laser emission means by the current supply means in response to a control signal externally input to the signal input means, and modulated by the current modulation means. Output varying means for changing a drive current supplied to the laser emitting means at a predetermined cycle.

Therefore, in the laser driving apparatus of the present invention, the driving current supplied to the laser emitting means by the current supplying means is modulated by the current modulating means in accordance with the control signal externally inputted to the signal input means. The laser beam emitted from the laser emitting means is modulated according to the control signal. Therefore, when this laser driving device is used in an electrophotographic image forming apparatus that forms a gradation image in dot units, a high-resolution image in which gradation is performed in dot units is formed. When the laser drive device supplies a drive current modulated in accordance with the control signal to the laser emission unit as described above,
Since the driving current is changed at a predetermined cycle by the output variable means, the emission intensity of the laser beam modulated according to the control signal is changed at a predetermined cycle. For this reason, when this laser drive device is used in an image forming apparatus, dots of the same size are not arranged in a portion where the density of the print image is constant, and the size is sequentially changed in a portion where the density of the print image changes sequentially. The changed dots are not arranged.

According to a seventh aspect of the present invention, there is provided a laser driving device.
A laser emitting unit that emits a laser beam in response to the supply of a driving current; a laser monitoring unit that monitors a laser beam emitted by the laser emitting unit to detect a light amount; Voltage holding means for temporarily holding a voltage, current supply means for generating a driving current corresponding to the holding voltage of the voltage holding means and supplying the driving current to the laser emitting means, and a control signal for the laser emitting means being externally input A signal input unit, a current modulation unit that modulates a drive current supplied to the laser emitting unit by the current supply unit in response to a control signal externally input to the signal input unit, and a dummy voltage that changes at a predetermined cycle. Output varying means for applying the voltage to the voltage holding means.

Therefore, in the laser driving apparatus of the present invention, when the laser emitting means emits a laser beam in response to the supply of the driving current, the laser beam is monitored by the laser monitoring means and the light amount is detected. The voltage corresponding to this detection result is temporarily held in the voltage holding means, and the drive current corresponding to the held voltage is generated by the current supply means and supplied to the laser emission means. It is maintained within the set predetermined range. In such a state, the drive current supplied to the laser emitting means by the current supplying means is modulated by the current modulating means in accordance with the control signal externally input to the signal input means, so that the laser emitted by the laser emitting means The beam is modulated according to the control signal. Therefore, when this laser driving device is used in an electrophotographic image forming apparatus that forms a gradation image in dot units, a high-resolution image in which gradation is performed in dot units is formed. As described above, when the current supply means supplies a drive current to the laser emission means in accordance with the holding voltage of the voltage holding means corresponding to the emission intensity of the laser drive device, a dummy voltage which changes in a predetermined cycle is output by the output variable means. Since the voltage is applied to the voltage holding means, the emission intensity of the laser beam modulated according to the control signal is changed at a predetermined cycle. For this reason,
When this laser driving device is used in an image forming apparatus, dots of the same size are not arranged in a portion where the density of a print image is constant, and dots whose size sequentially changes in a portion where the density of a print image sequentially changes. Are not arranged.

The laser driving device according to the invention of claim 8 is
A laser emitting unit that emits a laser beam in response to the supply of a driving current; a laser monitoring unit that monitors a laser beam emitted by the laser emitting unit and outputs a current signal corresponding to a light amount; A current supply unit that generates a drive current corresponding to the current signal to be output and supplies the drive current to the laser emission unit; a signal input unit to which a control signal of the laser emission unit is externally input; and a signal input unit that is externally input to the signal input unit. Current modulating means for modulating a drive current supplied to the laser emitting means by the current supplying means in response to a control signal, and an output for superimposing a dummy current changing at a predetermined period on a current signal outputted by the laser monitoring means. Variable means.

Therefore, in the laser driving device of the present invention, when the laser emitting means emits a laser beam in response to the supply of the driving current, the laser beam is monitored by the laser monitoring means and a current signal is output. Since the current supply means generates a drive current corresponding to the current signal and supplies the drive current to the laser emitting means, the emission intensity of the laser emitting means is maintained within a predetermined range set in advance. In such a state, the drive current supplied to the laser emitting means by the current supplying means is modulated by the current modulating means in accordance with the control signal externally input to the signal input means, so that the laser emitted by the laser emitting means The beam is modulated according to the control signal. Therefore, when this laser driving device is used in an electrophotographic image forming apparatus that forms a gradation image in dot units, a high-resolution image in which gradation is performed in dot units is formed. As described above, when the current supply means supplies a drive current to the laser emission means in response to the current signal of the laser monitor means corresponding to the emission intensity of the laser drive device, the output signal is changed to a current signal output by the laser monitor means. Is superimposed on the dummy current, the emission intensity of the laser beam modulated corresponding to the control signal is changed at a predetermined cycle. For this reason, when this laser drive device is used in an image forming apparatus, dots of the same size are not arranged in a portion where the density of the print image is constant, and the size is sequentially changed in a portion where the density of the print image changes sequentially. The changed dots are not arranged.

According to the ninth aspect of the present invention, there is provided the method as set forth in the fifth to eighth aspects.
The laser driving device according to any one of the above, further comprising a cycle generating means for generating a predetermined cycle irrespective of the operation cycle of the current modulating means, the synchronous in synchronization with the generation cycle of the cycle generating means The output varying means operates.

Therefore, when the cycle generating means generates a predetermined cycle irrespective of the operation cycle of the current modulating means, the output varying means changes the emission intensity of the laser beam in synchronization with the predetermined cycle. When the driving device is used in an image forming apparatus, it is possible to generate dots whose size changes at a predetermined cycle in a portion where the density of a print image is constant.

According to a tenth aspect of the present invention, there is provided the laser driving apparatus according to the ninth aspect, further comprising a cycle adjusting means for variably adjusting a generation cycle of the cycle generating means. Therefore, the generation period of the period generation unit is variably adjusted by the period adjustment unit. For example, when this laser driving device is used in an image forming apparatus, the period of the change in dot size is adjusted as desired. .

An eleventh aspect of the present invention is the laser driving device according to any one of the fifth to eighth aspects, further comprising a cycle generating means for generating a predetermined cycle synchronized with an operation cycle of the current modulating means. The output variable means operates in synchronization with the generation cycle of the cycle generation means.

Therefore, when the cycle generating means generates a predetermined cycle synchronized with the operation cycle of the current modulation means, the output varying means changes the light emission intensity of the laser beam in synchronization with the predetermined cycle. When the apparatus is used in an image forming apparatus, large and small size dots can be alternately generated in a portion where the density of a print image is constant.

An image forming apparatus according to a twelfth aspect of the present invention
12. A laser driver according to claim 5, a data supply unit for supplying image data as a control signal to a signal input unit of the laser drive unit, and the image data supplied by the data supply unit. Beam deflecting means for deflecting and scanning the laser beam emitted by the laser driving device in the main scanning direction; latent image carrying means for exposing and scanning with the laser beam deflected and scanned by the beam deflecting means; Sub-scanning means for moving the means relative to the beam deflecting means in the sub-scanning direction; latent image developing means for developing a latent image formed on the latent image holding means with toner; and developing by the latent image developing means. Toner transfer means for transferring the transferred toner of the latent image holding means to a recording medium, and a toner fixing means for fixing the toner transferred to the recording medium by the toner transfer means And, it is equipped with.

Therefore, in the image forming apparatus of the present invention, since the image data is supplied as a control signal to the signal input means of the laser driving apparatus of the present invention by the data supplying means, the laser emitting means of the laser driving apparatus is provided with the image data. And emits a laser beam modulated in accordance with. This laser beam is deflected and scanned in the main scanning direction by beam deflection means,
The latent image carrying means is exposed and scanned by the deflection-scanned laser beam, and the latent image carrying means thus exposed and scanned is relatively moved by the sub-scanning means in the sub-scanning direction with respect to the beam deflecting means. Thus, the latent image formed on the latent image carrying means is developed with the toner by the latent image developing means, and the developed toner of the latent image carrying means is transferred to the recording medium by the toner transferring means. Since the toner transferred to the recording medium is fixed by the toner fixing means, an image corresponding to the image data is formed on the recording medium by the electrophotography using the toner. According to the laser driving device of the present invention, even when the laser beam is modulated in dot units in accordance with the control signal, the emission intensity of the laser beam is changed at a predetermined cycle, so that the same size is used in a portion where the density of the print image is constant Are not arranged, and dots whose sizes are sequentially changed are not arranged in portions where the density of the print image is sequentially changed.

The various means referred to in the present invention only need to be formed so as to realize their functions. For example, dedicated hardware, a computer provided with appropriate programs by a program, a computer provided with an appropriate program , The functions realized inside, and the combination thereof are allowed.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a laser driving apparatus according to the present embodiment.
1 is a schematic vertical sectional side view showing a laser printer which is an image forming apparatus according to the present embodiment. FIG. 3 is a schematic diagram showing the relationship between the emission intensity of the semiconductor laser as the laser emitting means and the dot size, and FIG. 4 shows the relationship between the drive current and the dot size of the semiconductor laser according to the present embodiment and the prior art. It is a schematic diagram.

As shown in FIG. 1, the laser driving device 10 of the present embodiment includes a laser device 11.
The laser device 11 is provided integrally with a semiconductor laser 12 as a laser emitting unit and a photodiode 13 as a laser monitoring unit. Semiconductor laser 12
Emits a laser beam in response to the supply of drive current,
The photodiode 13 monitors a laser beam emitted from the semiconductor laser 12 and outputs a current signal corresponding to the amount of light.

A laser driver 14 corresponding to current supply means is connected to the laser device 11, and a hold capacitor 15 as voltage holding means is connected to the laser driver 14. The laser driver 14 also has a built-in voltage generation circuit (not shown) as voltage generation means, and this voltage generation circuit generates a voltage corresponding to a current signal that is a detection result of the photodiode 13.

The hold capacitor 15 temporarily holds the voltage generated by the voltage generation circuit corresponding to the detection result of the photodiode 13 at a predetermined sample hold cycle, and the laser driver 14 drives the drive current corresponding to the hold voltage of the hold capacitor 15. Is generated and supplied to the semiconductor laser 12.

The laser driver 14 includes a semi-fixed resistance element 16 and a PWM-IC (In
integrated circuit) 17 and this P
The WM-IC 17 is connected to a gate array 18 corresponding to signal input means. The semi-fixed resistance element 16 is a resistance element having a variable resistance value,
Adjusts the drive current supplied to the semiconductor laser 12.

The gate array 18 receives an external input of image data, which is a control signal of the semiconductor laser 12, and outputs a PW signal.
The M-IC 17 modulates a drive current supplied from the laser driver 14 to the semiconductor laser 12 in accordance with image data externally input to the gate array 18.

Then, the laser driving device 1 of the present embodiment
0, the output variable circuit 20 as the output variable means
OS (Complementary Metal Oxide Semiconducto)
r), the variable output circuit 20 is connected to the hold capacitor 15.

The output variable circuit 20 includes a high-speed switch 2
1 is applied to the hold capacitor 15 with a dummy voltage that changes in a predetermined cycle by the high-speed switching of
The drive current modulated by the M-IC 17 and supplied from the laser driver 14 to the semiconductor laser 12 is changed at a predetermined cycle. The semi-fixed resistance element 22 of the output variable circuit 20 is also a resistance element whose resistance value is variable,
To adjust the rate of change of the driving current due to.

The laser printer 30 of the present embodiment has a scanner motor 33 as shown in FIG.
The scanner motor 33 rotatably supports the polygon mirror 34 in the main scanning direction. This polygon mirror 3
The laser beam 4 is arranged on the optical axis of the semiconductor laser 12 of the laser driving device 10, and the laser beam emitted from the semiconductor laser 12 is deflected and scanned in the main scanning direction by a polygon mirror 34 driven to rotate by a scanner motor 33. So
Here, beam deflecting means is formed.

An fθ lens 35 and a reflection mirror 36 are sequentially arranged on the scanning optical path of the laser beam deflected and scanned as described above. Of the photosensitive drum 37 are opposed to each other. The photosensitive drum 37 is rotatably supported by a drum driving mechanism (not shown) serving as a sub-scanning means. The photosensitive drum 37 is driven to rotate by the drum driving mechanism, and the peripheral surface moves in the sub-scanning direction. I do.

On the peripheral surface of the photosensitive drum 37, a charging charger 38, a developing device 39 serving as a latent image developing means, a transfer roller 40 serving as a toner transferring means, and the like are arranged in order in opposition. It faces the peripheral surface of the photosensitive drum 37 from the gap between the charging charger 38 and the developing device 39.

The charging charger 38 charges the peripheral surface of the photosensitive drum 37 rotating in the sub-scanning direction by corona discharge.
Exposure and scanning are performed by the main scanning light reflected at 6 to form an electrostatic latent image. The developing device 39 develops the electrostatic latent image formed on the photosensitive drum 37 with toner, and the transfer roller 40 applies the toner on the photosensitive drum 37 developed by the developing device 39 to a printing paper P as a recording medium by a potential difference. Transcribe.

In the laser printer 30 of the present embodiment, a transport path 41 for the printing paper P is formed inside, and a paper feed tray 42 and a paper output tray 43 are arranged at both ends of the transport path 41. Printing paper P continuous from the paper feed tray 42
Is passed through a gap between the photosensitive drum 37 and the transfer roller 40, and a fixing device 44 serving as a toner fixing unit.
, And communicates with the paper discharge tray 43. The printing paper P is sequentially fed along a transport path 41 from a paper feeding tray 42 to a paper discharging tray 43, and the fixing device 44 transfers the toner transferred from the photosensitive drum 37 to the printing paper P by the transfer roller 40 as described above. Heat and press to fix.

The laser printer 30 of the present embodiment
Has a communication interface 45, and the printer controller 46 connected to the communication interface 45 controls the laser driving device 10 and the scanner motor 33.
And so on. The communication interface 45
A personal computer, a word processor, and the like are detachably connected by a connection connector (not shown), and image data is supplied from these. Printer controller 46
Controls the operation of the laser driving device 10 according to the image data, and synchronizes this operation with the rotation of the scanner motor 33.

The laser printer 30 according to the present embodiment
Is a mode setting circuit (not shown) which is mode setting means
Is provided, and various operation modes are switched and set by the mode setting circuit. As such an operation mode, for example, a normal image quality mode or a high image quality mode is set so as to be freely switchable. The output variable circuit 20 of the laser driving device 10 is stopped in the normal image quality mode and driven in the high image quality mode. You.

In the configuration described above, the laser printer 30 of the present embodiment uses the laser beam emitted from the semiconductor
An electrostatic latent image is formed on the printing paper P, and the image is formed by developing the electrostatic latent image with toner and transferring it to the printing paper P.

More specifically, in the laser printer 30 of the present embodiment, an electronic device such as a personal computer is connected to a communication interface 45, and image data externally input here is transferred to a printer controller 46. Since the printer controller 46 controls the operation of the laser driving device 10 according to the image data, the laser beam emitted from the semiconductor laser 12 by the laser driving device 10 is modulated according to the image data.

At the same time, the printer controller 46 controls the rotation of the polygon mirror 33 by the scanner motor 33, so that the laser beam emitted from the semiconductor laser 12 by the laser driver 10 is deflected by the polygon mirror 33 in the main scanning direction. Is done. The laser beam that has been deflected and scanned is optically corrected by the fθ lens 35, is reflected by the reflection mirror 36, and is irradiated on the peripheral surface of the rotating photosensitive drum 37 that moves in the sub-scanning direction.

Since the peripheral surface of the photosensitive drum 37 is charged in advance by corona discharge of the charging charger 38, the photosensitive drum 37 is exposed and scanned by a laser beam to form an electrostatic latent image. The electrostatic latent image formed on the peripheral surface of the photosensitive drum 37 is developed with the toner supplied from the developing device 39, and is transferred onto the printing paper P fed from the paper feed tray 42 through the transport path 41 by the transfer roller 40. Transcribed.

The printing paper P to which the toner has been transferred is fed to the fixing device 44 through the transport path 41, where it is heated and pressed to fix the toner. The printing paper P on which the toner has been fixed in this way is fed through the transport path 41 and discharged to the paper discharge tray 43. Thus, the image formation by the laser printer 30 is completed.

The laser driving device 10 of the present embodiment drives the semiconductor laser 12 as a part of the laser printer 30 as described above. The drive current supplied to the semiconductor laser 12 by the laser driver 14 is controlled by a PWM-IC 17 corresponding to image data externally input to the gate array 18.
Therefore, the laser beam emitted from the semiconductor laser 12 is modulated according to the image data.

That is, the laser driving device 1 of the present embodiment
0 indicates that the emission intensity of the semiconductor laser 12 is modulated in dot units corresponding to the image data as shown in FIG.
The laser printer 30 according to the present embodiment can form a high-resolution image toned in dot units.

In order to ensure good image quality of the laser printer 30, the laser driving device 10
The emission intensity of the semiconductor laser 12 is feedback-controlled. For example, when the normal image quality mode is set as the operation mode, the laser beam emitted from the semiconductor laser 12 is monitored by the photodiode 13 and a current signal corresponding to the light amount is output. Is generated by the voltage generation circuit and sampled and held in the hold capacitor 15 at a predetermined cycle.

Since a drive current corresponding to the holding voltage of the hold capacitor 15 is generated by the laser driver 14 and supplied to the semiconductor laser 12, for example, as shown in FIGS. In a certain portion, the drive current of the laser driver 14 is kept constant and the light emission intensity of the semiconductor laser 12 is kept constant, so that dots of a fixed size are arranged in the printed image. Similarly, in the portion (not shown) where the density of the print image changes sequentially, dots whose size changes sequentially are arranged.

However, the laser driving device 1 of the present embodiment
For example, when the high image quality mode is switched and set as the operation mode, the light emission intensity of the semiconductor laser 12 is changed at a predetermined cycle. More specifically, when the laser driver 14 supplies a drive current to the semiconductor laser 12 as described above,
A dummy voltage that changes at a predetermined cycle is applied to the hold capacitor 15 by the output variable circuit 20.

Then, as shown in FIG. 4 (c), the driving current supplied to the semiconductor laser 12 by the laser driver 14 is changed at a predetermined cycle in accordance with the holding voltage of the holding capacitor 15, so that the image data is The emission intensity of the correspondingly modulated laser beam is varied at a predetermined cycle.

As shown in FIG. 6D, the dot size is periodically changed even in the portion where the image density is constant as described above, and the size is sequentially changed in the portion (not shown) where the image density changes sequentially. The changed dots are not arranged. In addition,
Such a periodic change in the dot size is performed simultaneously with the adjustment of the dot size based on the image data, so that the output variable circuit 20 periodically changes the basic size of the dot whose size is adjusted according to the image data. Will be done.

For example, when the dot size is changed from "2 to 4" in accordance with the image data, in the portion where the dot size corresponding to the image data is "2", the dot size is "1, 3". Are alternately changed. Similarly, the dot size of “3” is alternately changed to “2, 4”, and the dot size of “4” is alternately changed to “3, 5”.

In the laser printer 30 of the present embodiment,
As described above, since the dot size of the print image is periodically changed in a state corresponding to the image data, when the print image is visually observed, the image density corresponds to the image data. However, since the size of each dot of the printed image is periodically changed, for example, moiré is unlikely to occur in a portion where the image density is constant or a portion that changes continuously, thereby improving visual image quality. Can be done.

In particular, the laser printer 30 of the present embodiment
In the above, the presence / absence of the above-mentioned periodic variable control of the dot size can be switched and set by the operation mode, so that the print image can be formed by the same method as the conventional method, and the image can be formed by a desired method. it can.

As described above, various settings can be made for the cycle of changing the dot size. For example,
As in a laser driving device 50 shown as a first modified example in FIG. 5, an oscillator 51 can be provided as a period generating means, and this oscillator 51 can be connected to the high-speed switch 21 of the output variable circuit 20.

In this case, the oscillator 51 is connected to the PWM-IC 17
The output variable circuit 20 changes the light emission intensity of the laser beam in synchronization with the generation cycle regardless of the operation cycle of the laser beam. For this reason, it is possible to generate a dot whose size changes at a predetermined cycle irrelevant to image formation in a portion where the density of the print image of the laser printer 30 is constant.

Further, it is also possible to connect a volume (not shown) or the like as a period adjusting means to the above-described oscillator 51 and variably adjust the generation period of the oscillator 51 by using this volume. In this case, since the dot size change cycle can be adjusted as desired, the user can adjust the image quality as desired.

A data processing circuit 61 is provided as a period generating means as in a laser driving device 60 shown as a second modification in FIG. 6, and this data processing circuit 61 is connected to the gate array 18 and an output variable circuit. It is also possible to connect to 20 high-speed switches 21.

In this case, a predetermined cycle synchronized with image data externally input to the gate array 18 is determined by the data processing circuit 6.
1 occurs, and the output variable circuit 20
Changes the emission intensity of the laser beam. Therefore, large and small size dots can be alternately generated in a portion where the density of the print image of the laser printer 30 is constant.

Further, in the above-described laser driving device 10 and the like, since the emission current of the semiconductor laser 12 is periodically changed by periodically changing the drive current of the laser driver 14, the output variable The application of the dummy voltage has been exemplified.

However, by superimposing the dummy current on the current signal output from the photodiode 13, the driving current of the laser driver 14 can be changed periodically, so that the emission intensity of the semiconductor laser 12 can be changed periodically. It is. In that case, an output variable circuit 71 as an output variable means may be connected to the photodiode 13 as in a laser driving device 70 shown as a third modification in FIG.

Such an output variable circuit 71 is, for example,
It can be realized by connecting a plurality of current sources 72 to the photodiode 13 via a high-speed switch 73 and connecting an oscillator 74 to the high-speed switch 73 as a period generating means.
For example, the currents generated by the four current sources 72 are “1, 2, 3,
In the case of “4 (A)”, if these are selected by the high-speed switch 73, a dummy current that changes by 1 (A) from “1 to 10 (A)” can be generated.

Such a change period of the dummy current can be made independent of synchronization with the image data. Further, as a procedure for changing a large number of dummy currents as described above, it is possible to change the current values in a stepwise order and to change the current values in a random order.

[0073]

Since the present invention is configured as described above, it has the following effects.

The laser driving method according to the first aspect of the present invention
By changing the emission intensity of the modulated laser beam emitted by the laser emission means at a predetermined cycle,
When the laser driving method of the present invention is applied to an electrophotographic image forming apparatus that forms a gradation image in dot units, dots of the same size are not arranged in a portion where the density of a print image is constant, and printing is performed. Since the dots whose sizes are sequentially changed are not arranged in the portion where the density of the image is sequentially changed, the visual quality of the printed image can be improved.

The laser driving method according to the second aspect of the present invention
By changing the drive current supplied from the current supply unit to the laser emission unit at a predetermined cycle, the laser drive method of the present invention is used for an electrophotographic image forming apparatus that forms a gradation image in dot units. In this case, dots of the same size are not arranged in a portion where the density of the print image is constant, and dots whose sizes are sequentially changed are not arranged in a portion where the density of the print image changes sequentially. The visual quality of the image can be improved.

The laser driving method according to the third aspect of the present invention
By applying a dummy voltage that changes at a predetermined cycle to the voltage holding means, when the laser driving method of the present invention is applied to an electrophotographic image forming apparatus that forms a gradation image in dot units, a print image is generated. Since the dots of the same size are not arranged in the portion where the density of the printed image is constant, and the dots whose size is sequentially changed are not arranged in the portion where the density of the printed image is sequentially changed. Quality can be improved.

The laser driving method according to the fourth aspect of the present invention
By superimposing a dummy current that changes at a predetermined cycle on a current signal output from the laser monitoring unit to the current supply unit, the laser driving method of the present invention can be applied to an electrophotographic system that forms a gradation image in dot units. When used in an image forming apparatus, dots of the same size are not arranged in a portion where the density of the printed image is constant, and dots of sequentially changed size are arranged in a portion where the density of the printed image is sequentially changed. Therefore, the visual quality of the printed image can be improved.

The laser driving device according to the fifth aspect of the present invention
A laser emitting unit that emits a laser beam in response to the supply of the driving current, a current supplying unit that generates a predetermined driving current and supplies the laser emitting unit, and a control signal of the laser emitting unit is externally input. Signal input means, current modulation means for modulating a drive current supplied to the laser emission means by the current supply means in response to a control signal externally input to the signal input means, and modulated by the current modulation means. Output varying means for changing the emission intensity of the laser beam emitted by the laser emitting means in a predetermined cycle in accordance with the driving current, so that the laser driving apparatus of the present invention can be used to convert a gradation image into dot images. When the image forming apparatus is used in an electrophotographic image forming apparatus for forming an image, dots of the same size are not arranged in a portion where the density of the print image is constant, and the density of the print image sequentially changes. Since nor sequentially changed dots are arranged sized portions, it is possible to improve the quality of the visual printed image.

The laser driving device according to the sixth aspect of the present invention
A laser emitting unit that emits a laser beam in response to the supply of the driving current, a current supplying unit that generates a predetermined driving current and supplies the laser emitting unit, and a control signal of the laser emitting unit is externally input. Signal input means, current modulation means for modulating a drive current supplied to the laser emission means by the current supply means in response to a control signal externally input to the signal input means, and modulated by the current modulation means. An output varying means for changing a driving current supplied to the laser emitting means at a predetermined period, and an electrophotographic image forming a gradation image in dot units by the laser driving apparatus of the present invention. When used in a forming apparatus, dots of the same size are not arranged in a portion where the density of the printed image is constant, and the size is sequentially changed in a portion where the density of the printed image is sequentially changed. Since no dots are arranged, it is possible to improve the quality of the visual printed image.

According to a seventh aspect of the present invention, there is provided a laser driving device comprising:
A laser emitting unit that emits a laser beam in response to the supply of a driving current; a laser monitoring unit that monitors a laser beam emitted by the laser emitting unit to detect a light amount; Voltage holding means for temporarily holding a voltage, current supply means for generating a driving current corresponding to the holding voltage of the voltage holding means and supplying the driving current to the laser emitting means, and a control signal for the laser emitting means being externally input A signal input unit, a current modulation unit that modulates a drive current supplied to the laser emitting unit by the current supply unit in response to a control signal externally input to the signal input unit, and a dummy voltage that changes at a predetermined cycle. An output variable means for applying the voltage to the voltage holding means. When using the image forming apparatus,
Since dots of the same size are not arranged in a portion where the density of the print image is constant, and dots whose sizes are sequentially changed are not arranged in a portion where the density of the print image is sequentially changed. The above quality can be improved.

The laser driving device according to the eighth aspect of the present invention
A laser emitting unit that emits a laser beam in response to the supply of a driving current; a laser monitoring unit that monitors a laser beam emitted by the laser emitting unit and outputs a current signal corresponding to a light amount; A current supply unit that generates a drive current corresponding to the current signal to be output and supplies the drive current to the laser emission unit; a signal input unit to which a control signal of the laser emission unit is externally input; and a signal input unit that is externally input to the signal input unit. Current modulating means for modulating a drive current supplied to the laser emitting means by the current supplying means in response to a control signal, and an output for superimposing a dummy current changing at a predetermined period on a current signal outputted by the laser monitoring means. , The laser driving device of the present invention is useful for an electrophotographic image forming apparatus that forms a gradation image in dot units. In this case, dots of the same size are not arranged in a portion where the density of the print image is constant, and dots whose sizes are sequentially changed are not arranged in a portion where the density of the print image changes sequentially. The visual quality of the image can be improved.

The ninth aspect of the present invention relates to the fifth to eighth aspects.
The laser driving device according to any one of the above, further comprising a cycle generating means for generating a predetermined cycle irrespective of the operation cycle of the current modulating means, the synchronous in synchronization with the generation cycle of the cycle generating means By operating the output variable means, when the laser drive device of the present invention is used in an image forming apparatus, it is possible to generate dots whose size changes at a predetermined cycle in a portion where the density of a print image is constant. Further, the visual quality of the printed image can be improved.

According to a tenth aspect of the present invention, there is provided the laser driving apparatus according to the ninth aspect, further comprising a cycle adjusting means for variably adjusting a generation cycle of the cycle generating means. When the laser driving device is used in an image forming apparatus, the period of the change in the dot size can be adjusted as desired, so that the image quality of the image to be formed can be adjusted as desired.

An eleventh aspect of the present invention is the laser driving device according to any one of the fifth to eighth aspects, further comprising a period generating means for generating a predetermined period synchronized with the operation period of the current modulating means. The output variable means operates in synchronization with the generation cycle of the cycle generation means, so that when the laser driving device of the present invention is used in an image forming apparatus, the density of a print image is large or small in a fixed portion. Since dots of a size can be generated alternately, the visual quality of a printed image can be further improved.

According to a twelfth aspect of the present invention, there is provided an image forming apparatus comprising:
12. A laser driver according to claim 5, a data supply unit for supplying image data as a control signal to a signal input unit of the laser drive unit, and the image data supplied by the data supply unit. Beam deflecting means for deflecting and scanning the laser beam emitted by the laser driving device in the main scanning direction; latent image carrying means for exposing and scanning with the laser beam deflected and scanned by the beam deflecting means; Sub-scanning means for moving the means relative to the beam deflecting means in the sub-scanning direction; latent image developing means for developing a latent image formed on the latent image holding means with toner; and developing by the latent image developing means. Toner transfer means for transferring the transferred toner of the latent image holding means to a recording medium, and a toner fixing means for fixing the toner transferred to the recording medium by the toner transfer means In the image forming apparatus of the present invention, even when the laser beam is modulated in dot units in response to the control signal, the emission intensity of the laser beam is changed at a predetermined period, Dots of the same size are not arranged in a portion where the density of the image is constant, and dots of a size that is sequentially changed are not arranged in a portion where the density of the printed image changes sequentially, so that the visual quality is good. Image can be formed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a laser driving device according to an embodiment of the present invention.

FIG. 2 is a schematic vertical sectional side view showing a laser printer as an embodiment of the image forming apparatus of the present invention.

FIG. 3 is a schematic diagram showing a relationship between a semiconductor laser as a laser emitting unit, emission intensity, and dot size.

FIG. 4 is a schematic diagram illustrating a relationship between a drive current of a semiconductor laser and a dot size.

FIG. 5 is a block diagram illustrating a main part of a laser driving device according to a first modified example.

FIG. 6 is a block diagram illustrating a main part of a laser driving device according to a second modification.

FIG. 7 is a block diagram illustrating a main part of a laser driving device according to a third modification.

[Explanation of symbols]

 Reference Signs List 10 laser driving device 12 semiconductor laser serving as laser emitting means 13 photodiode serving as laser monitoring means 14 laser driver corresponding to current supplying means 15 hold capacitor serving as voltage holding means 17 PWM-IC corresponding to current modulating means 18 signal input Gate array 20 corresponding to the means 20 output variable circuit as output varying means 30 laser printer as image forming apparatus 34 polygon mirror as beam deflecting means 37 photosensitive drum as latent image holding means 39 developing device as latent image developing means Reference Signs List 40 Transfer roller serving as toner transfer unit 44 Fixing unit serving as toner fixing unit 50 Laser drive unit 51 Oscillator serving as cycle generation unit 60 Laser drive unit 61 Data processing circuit serving as cycle generation unit 70 Laser drive unit 71 Output change unit Variable output circuit P Printing paper as a recording medium

Claims (12)

[Claims] 1. A laser driving method for modulating a laser beam emitted from a laser emitting unit in response to a control signal input from the outside, wherein the laser emitting unit emits a modulated laser beam emitted from the laser emitting unit. A laser driving method wherein the intensity is changed at a predetermined cycle. 2. When a driving current is supplied from a current supply unit to a laser emitting unit to emit a corresponding amount of laser beam, the current supplying unit transmits the laser beam to the laser emitting unit in response to a control signal input from the outside. A laser driving method that modulates a supplied driving current, wherein the driving current supplied from the current supply unit to the laser emitting unit is changed at a predetermined cycle. . 3. When a drive current is supplied from a current supply unit to a laser emitting unit to emit a corresponding amount of laser beam, the amount of the laser beam is monitored by a laser monitor unit and a corresponding voltage is stored in a voltage holding unit. The driving current corresponding to the holding voltage of the temporary holding is generated by the current supply unit and supplied to the laser emitting unit. The driving current supplied in this manner corresponds to a control signal externally input. A laser drive method for performing modulation by applying a dummy voltage that changes at a predetermined cycle to the voltage holding means. 4. When a drive current is supplied from a current supply unit to a laser emitting unit to emit a corresponding amount of laser beam, the laser beam is monitored by a laser monitor unit and a current signal corresponding to the amount of light is output. A drive current corresponding to the current signal is generated by the current supply unit and supplied to the laser emission unit, and the drive current supplied in this manner is modulated according to a control signal input from the outside. A laser driving method, wherein a dummy current that changes at a predetermined cycle is superimposed on a current signal output from the laser monitoring unit to the current supply unit. 5. A laser emitting means for emitting a laser beam in response to the supply of a driving current, a current supplying means for generating a predetermined driving current and supplying it to the laser emitting means, and a control signal for the laser emitting means. A signal input means externally input; a current modulation means for modulating a drive current supplied to the laser emitting means by the current supply means in response to a control signal externally input to the signal input means; A laser driving device comprising: a variable output means for changing a light emission intensity of a laser beam emitted from the laser emitting means at a predetermined cycle in accordance with a drive current modulated by the means. 6. A laser emitting unit that emits a laser beam in response to the supply of a driving current, a current supplying unit that generates a predetermined driving current and supplies the driving beam to the laser emitting unit, and a control signal of the laser emitting unit. A signal input means externally input; a current modulation means for modulating a drive current supplied to the laser emitting means by the current supply means in response to a control signal externally input to the signal input means; A laser output device comprising: a variable output means for changing a drive current supplied to the laser emission means at a predetermined cycle after being modulated by the means. 7. A laser emitting means for emitting a laser beam in response to the supply of a drive current, a laser monitoring means for monitoring a laser beam emitted by the laser emitting means and detecting an amount of light, Voltage holding means for temporarily holding a voltage corresponding to the detection result; current supply means for generating a driving current corresponding to the holding voltage of the voltage holding means and supplying the driving current to the laser emitting means; and a control signal for the laser emitting means A signal input means externally input; a current modulation means for modulating a drive current supplied to the laser emitting means by the current supply means in response to a control signal externally input to the signal input means; A laser driving device comprising: an output variable unit that applies a changing dummy voltage to the voltage holding unit. 8. A laser emitting means for emitting a laser beam in response to supply of a driving current, a laser monitoring means for monitoring a laser beam emitted by the laser emitting means and outputting a current signal corresponding to a light amount, Current supply means for generating a drive current corresponding to the current signal output by the laser monitor means and supplying the drive current to the laser emission means; signal input means for externally inputting a control signal of the laser emission means; Current modulation means for modulating a drive current supplied to the laser emitting means by the current supply means in response to a control signal externally input to the means; and a dummy which changes at a predetermined cycle to a current signal output by the laser monitoring means. A laser driving device comprising: an output variable means for superimposing a current. 9. A cycle generating means for generating a predetermined cycle independently of an operating cycle of said current modulating means, wherein said output variable means operates in synchronization with a generating cycle of said cycle generating means. The laser drive device according to any one of claims 5 to 8. 10. The laser driving apparatus according to claim 9, further comprising a cycle adjusting means for variably adjusting a generation cycle of said cycle generating means. 11. The apparatus according to claim 5, further comprising a cycle generating means for generating a predetermined cycle synchronized with an operation cycle of said current modulating means, wherein said output variable means operates in synchronization with a generation cycle of said cycle generating means. 9. The laser driving device according to any one of claims 8 to 8. 12. A laser driving device according to claim 5, a data supply unit for supplying image data as a control signal to a signal input unit of the laser driving unit, and the data supply unit supplies the image data. Beam deflecting means for deflecting and scanning the laser beam emitted by the laser driving device in the main scanning direction in accordance with image data to be scanned, and latent image holding means for exposure and scanning with the laser beam deflected and scanned by the beam deflecting means. Sub-scanning means for moving the latent image carrying means relative to the beam deflecting means in the sub-scanning direction; latent image developing means for developing a latent image formed on the latent image carrying means with toner; A toner transfer unit for transferring the toner of the latent image holding unit developed by the image developing unit to a recording medium; and a toner transfer unit for determining the toner transferred to the recording medium by the toner transfer unit. Image forming apparatus that includes a toner fixing device, the for.