JPS62279368A - Image forming device - Google Patents

Abstract

PURPOSE:To control line width perpendicular to a main scanning direction by specifying a scanning period of one picture element as the smallest constitution unit in the main scanning direction on an image on a photosensitive body and varying the period of laser light emission corresponding to the specified scanning period. CONSTITUTION:Image data STD1 outputted by an external device 50 is supplied to a laser turn-on time control part 48 as it is through an image data controller 47 in synchronism with a clock signal VCKLphi. Then, the laser turn-on time control part 48 outputs a signal LDDRVphi which controls the time when a semiconductor laser 11 is turned on in a scanning section of one picture element according to the supplied image data. Therefore, a laser driving part 46 varies the output timing of a driving current according to the signal LDDRVphi.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to an image forming apparatus that performs dot printing, such as a laser printer.

(Prior Art) In general, a laser printer uses a laser as a light source and applies an electrophotographic process, and its laser scanning system uses, for example, the one shown in FIG. 10. That is, the light from the semiconductor laser 1 is made into parallel light by a collimator lens 2, reflected by a polygon mirror 3, and the reflected light is irradiated onto a photosensitive drum 6 through an f/θ lens 5. The polygon mirror 3 is rotated in a constant direction A at a constant speed by a mirror motor 4.

Therefore, the laser beam on the photosensitive drum 6 is scanned in one direction. On the other hand, since the photosensitive drum 6 is rotating in one direction C at a constant speed, the semiconductor laser 1
By modulating the brightness, a latent image can be formed on the surface of the photosensitive drum 6.

However, in laser printers such as those described above, it is desired that the size of one dot (pixel) be variously specified by the user. Further, it is desired that the thickness of the vertical lines and horizontal lines be varied. However, known methods for changing the line thickness in the main scanning direction include changing the beam shape on the surface of the photoreceptor drum and changing laser power.

As a result, by the method of changing the beam shape,
The thickness of the line in the direction perpendicular to the main scanning direction is controlled, but in principle the line thickness cannot be reduced beyond a certain level to less than the line width equivalent to one dot. there were. In addition, in the method of changing the laser power, due to the difference in development characteristics between the main scanning direction and the sub-scanning direction, it is necessary to always maintain a balance between the width of the line in the main scanning direction (horizontal line) and the width of the line in the sub-scanning direction (vertical line). It was difficult to keep it constant. Furthermore, with this method, it was not possible to change the line width in the sub-scanning direction without changing the line width in the main-scanning direction.

(Problems to be Solved by the Invention) This invention eliminates the drawback of not being able to control the line width in the direction perpendicular to the main scanning direction. An object of the present invention is to provide an image forming apparatus that can change the line width in the main scanning direction without affecting the line width in the sub-scanning direction. do.

[Structure 1 of the Invention (Means for Solving the Problems) The image forming apparatus of the present invention includes a laser beam emitting unit that emits a laser beam according to image data, and a scanning device that deflects the laser beam from the laser beam emitting unit. and an image forming means that forms a dot-shaped latent image on a photoreceptor using laser light from the scanning means, one pixel is the smallest constituent unit in the main scanning direction on the image on the photoreceptor. The scanning device includes a specifying means for specifying a scanning period of minutes, and a controlling means for changing the period during which the laser beam is emitted in accordance with the scanning period specified by the specifying means.

(Function) This invention specifies a scanning period for one pixel, which is the minimum constituent unit in the main scanning direction on an image on a photoreceptor, and changes the period during which laser light is emitted in accordance with the specified scanning period. It was designed to do so.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 2 shows the overall configuration of the laser printer. That is, the laser light from the semiconductor laser (oscillator) 11 is made into parallel light by the collimator lens 12 and reflected by the polygon mirror 13, and the reflected light is reflected by the θ lens 1.
4 and is imaged onto the photoreceptor drum 17 via mirrors 15 and 16.

The photosensitive drum 17 rotates in the direction of the arrow shown in the figure, and is first charged by a charger 18, and then exposed to an image by the semiconductor laser 11, forming an electrostatic latent image on its surface. This electrostatic latent image is made into a visible image by adhering toner 1 to 1 by one developing device, and this toner image is transferred to the sheet P by the transfer charger 20.
The toner image is transferred to the paper P by being charged with electricity. Photosensitive drum 17 after transfer
By being reversely charged by the charger 21, the previous charge is removed.

On the other hand, the paper P is delivered from the selected upper paper feed cassette 22 or lower paper feed cassette 23 to the delivery row 524 or 2.
5, the sheets are taken out one by one, guided through a paper guide path 26 or 27 to a pair of registration rollers 28.2, and sent to a transfer section by a pair of rollers 28.29. The paper P sent to the transfer section is brought into close contact with the surface of the photoreceptor drum 17 at the portion of the transfer charger 20, and the photoreceptor drum 17 is moved by the action of the charger 2o.
The upper toner image is transferred. The transferred paper P is peeled off from the photoreceptor drum 17 by the action of the peeling charger 30 and conveyed by the conveyor belt 31, and is sent to the fixing device 32 provided at the end of the conveyor belt. The transferred image is fixed.

After fixing, the paper P is discharged onto a tray 34 by a pair of paper discharge rollers 33, 33.

FIG. 1 shows a laser drive circuit for driving the semiconductor laser 11. As shown in FIG. That is, the semiconductor laser 11
, a light amount detection unit 41 that outputs an electric signal corresponding to the intensity of the laser light emitted from the semiconductor laser 11, a reference level (of the laser light emitted from the semiconductor laser 11),
The beam light setting section 42 outputs an electrical signal corresponding to the set value>, and the signal (detection value) from the light amount detection section 41 is compared with the setting value from the beam light setting section 42, and this comparison is performed. A comparison amplification section 43 that outputs the difference only when the result is [detected value minus set value J; a sample hold section 44 that samples and holds the signal from this comparison amplification section 43;
A current amplification section 45 amplifies the output from the sample and hold section 44, and the current from the current amplification section 45 is applied to the base of a transistor (not shown) to drive the semiconductor laser 11 according to the current. A laser drive section 46 that changes the current and changes the output timing of the drive current according to a signal LDDRVΦ supplied from a laser lighting 'R period control section 48, which will be described later.
, an image data controller 47 that outputs the image data STD supplied from the external device 50 as it is in synchronization with the drive signal VCLKφ, and this image data controller 4
a laser lighting time control unit 48 that outputs a signal LDDRVφ for controlling the lighting time of the semiconductor laser 11 for one pixel scanning period in accordance with the image data LOTφ supplied from the semiconductor laser 11; The laser bias current setting section 49 sets a reference bias current to .

The light amount detection section 41, the beam light 11 setting section 42, the comparison amplification section 43, the sample hold section 44, the current amplification section 45,
A stabilizing circuit is constituted by the laser drive unit 46, and this stabilizing circuit adjusts the output of the semiconductor laser 11 to a peak level corresponding to the reference level.

As shown in FIG.
The circuit includes an OR time constant circuit 57 consisting of a capacitor 56 and an amplifier 58. As a result, image data LDTφ as shown in FIG. 4(a) from the image data controller 47 is supplied to the OR time constant circuit 57 via the NAND circuit 51 in synchronization with the tarok. Then, the OR time constant circuit 57 outputs a signal whose rise is slowed down according to the CR time constant, as shown in FIG. 2(b).

This output has chattering removed by a Schmitt IC constituted by NAND circuits 52 and 53, and is supplied to a NAND circuit 54. As a result, the NAND circuit 53 outputs a signal at -day- level when the level is above a predetermined level, and outputs a signal at 'L- level when the level is below the predetermined level, as shown in FIG. It is supposed to be done. Therefore, the NAND circuit 54 outputs a signal obtained by inverting the logical product of the output of the NAND circuit 53 and the output of the NAND circuit 51, as shown in FIG. 3(d). The output of this NAND circuit 54 is amplified by an amplifier 58,
Signal LDDRVφ for lighting control of the semiconductor laser 11
is output as

The resistance value of the variable resistor 55 in the OR time constant circuit 57 is changed to a resistance value corresponding to the line width specified by the user at the time of manufacturing the device, thereby changing the time constant and outputting the signal. The rise of the time is now different.

This allows the lighting time of the laser beam to be changed.

In this case, when print data of continuous pixels is supplied, the lighting control signal LDDRVφ (= H-1-L) is activated only when the data changes from white to black or from black to white.
-) is changed, it is possible to prevent the color from changing at each pixel, and the image does not become uneven, making it possible to draw something beautiful.

Thereby, even when line width control is performed, image formation of consecutively printed pixels for a plurality of pixels can be smoothly performed. In this case, since there is no check on what kind of signal will come next, etc., it can be realized with a simple circuit.

FIG. 5 shows the relationship between the laser beam intensity distribution scanned on the photosensitive drum 17 and image characteristics.

That is, it is assumed that the spatial distribution of scanning exposure energy by laser scanning on the photosensitive drum 17 is as shown in FIG. As a result, the photosensitive characteristics (■) and the reversal phenomenon characteristics (
(including the effects of transfer and fixing)), the image characteristics ■ are obtained.

The scanning exposure characteristics shown by the solid line in the figure are laser light output of 5mW.
This is a simulation, and the image characteristics are that the lines are slightly thinner. In this case, the exposure energy is 2μS
/ CD, the surface potential of the photoreceptor drum 17 is 300
In ■, the reflection density is 0.4 and the distance in the sub-scanning direction is 4.
It is 0 μm to −40 μm. On the other hand, the scanning exposure characteristics shown by the broken line are obtained with a laser light output of 8 mW, and it can be seen that this makes the line thicker. In this case, when the exposure energy is 2 μS/i, the photosensitive drum 17
When the surface potential at is 300V, the reflection density is 0.4,
The distance in the sub-scanning direction is 55 μm to −55 μm.

Ma Therefore, by increasing the light l, the scanning-like It can be seen that the width of the direction line (V line) becomes thicker.

Next, the operation in such a configuration will be explained.

For example, now image data S output from the external device 50
The TD beam is supplied directly to the laser lighting time control unit 48 via the image data controller 47 in synchronization with the TD beam open signal VCLKφ. Then, the laser lighting time control section 48
outputs a signal LDDRVφ that controls the lighting time of the semiconductor laser 1 for one pixel scanning period in accordance with the supplied image data LDTφ.

For example, the image data LDTφ from the image data controller 47 is sent to the NAND circuit 51 in synchronization with the clock.
is supplied to the CR time constant circuit 57 via. Then, C
The R time constant circuit 57 outputs a signal whose rise is slowed according to the CR time constant. This output has chattering removed by a Schmitt IC constituted by NAND circuits 52 and 53, and is supplied to a NAND circuit 54.

As a result, as the output of the NAND circuit 53, a signal of -H- level is output when the level is above a predetermined level, and a signal of -1 level is output when the level is below the predetermined level. Therefore, the NAND circuit 54 outputs a signal obtained by inverting the AND of the output of the NAND circuit 53 and the output of the NAND circuit 51. The output of this NAND circuit 54 is amplified by an amplifier 58, and a signal LDDR for controlling the lighting of the semiconductor laser 11 is generated.
It is output to the laser drive section 46 as Vφ.

Thereby, the laser drive unit 46 changes the output timing of the drive current according to the signal LDDRVφ supplied from the laser lighting time control unit 48.

Therefore, when image data as shown in FIG. 6(a) is output from the external device 50, the semiconductor laser 11
The output of the laser beam is as shown in FIG. 3(b).

As a result, the image on the paper P after development and fixing is shown in the same figure (C).
It becomes as shown in . The shaded area in FIG. 2A indicates the area where toner should be applied. In addition, FIG.
S indicates an area where the laser light is on, and a white background indicates that the laser light is off. The shaded area in FIG. 2C indicates the area where the toner is deposited. However, in this figure, the width in the sub-scanning direction has no meaning.

Note that the reason why toner remains on the area where the laser beam is turned off in the main scanning direction after the appearance is due to the diameter of the laser beam.
This is because the toner is crushed and spread when it is fixed. At this time, as an example, the laser power and the beam diameter in the sub-scanning direction are set to be exactly equal to the width of one pixel. In this way, since the output time of the laser beam is controlled only by changing the signal level, the thickness of the line (vertical line) in the sub-scanning direction can be freely controlled. Furthermore, lines in the main scanning direction do not become white in the middle of the line, that is, no unevenness occurs, and the line width does not change.

In the above example, the laser lighting time control section 48 was provided between the image data controller 47 and the laser drive section 46, but it is provided between the laser drive section 46 and the semiconductor laser 11, and the laser power control section 48 is provided between the laser drive section 46 and the semiconductor laser 11. It may also be a case of controlling the rise time of .

As described above, by changing the time constant of the CR time constant circuit 57 in the laser lighting time control section 48 according to the user's request, lines in the sub-scanning direction can be The width of the image can be changed to any desired width, and lines in the main scanning direction do not become uneven, making it possible to draw clean images.

In the above embodiment, the width of the line in the sub-scanning direction is controlled by controlling the image data supplied to the laser drive section by the image data controller and changing the output timing of the drive current from the laser drive section. The width can be changed to an arbitrary width, but the present invention is not limited to this. The drive current output from the laser drive unit to the semiconductor laser has a transient output, that is, an overshoot, and the level (height width) of this overshoot can be changed. By doing so, the width of the line in the M1 scanning direction may be changed to an arbitrary width.

For example, as shown in FIG.
A laser transient output control section 60 is provided between the laser diode 46 and the semiconductor laser 11 . This laser transient output control section 61
As shown in the figure, the frequency response is lower than that of the image clock, and the operational amplifier 61, resistor 62, 63, diode 64, and the level (height) of the above-mentioned overshoot are adjusted to produce an overshoot (transient output). It is constituted by a variable pull capacitor 65. In this case, as the level of overshoot increases, the amount of toner adhering to the photosensitive drum, ie, the paper, increases, and the toner becomes wider after fixing.

Therefore, when image data as shown in FIG. 9(a) is output from the external device 50, the transient output from the laser transient output control section 60 becomes as shown in FIG. 9(b). As a result, the image on paper P after fixation is as shown in the same figure (C
). The shaded area in FIG. 2A indicates the area where toner should be applied. FIG. 5B shows control of the transient output at the point where the output of the laser beam changes. Furthermore, the shaded area in FIG. 2C indicates the area on which the toner is deposited. However, in this figure, gl
Paddling in the scanning direction has no meaning.

As a result, by adjusting the overshoot level using the barrier pull capacitor 65, the toner amount can be changed, and the line width in the -1 scanning direction can be changed without changing the line width in the main scanning direction. It can be changed to any width.

In addition, since the transient output of the laser beam is controlled when changing from white to black and from black to white, the thickness of the line in the sub-scanning direction can be freely controlled. , other colors do not enter the line in the main scanning direction, and the line width does not change.

In addition, by controlling the laser bias current in the laser bias current setting section, that is, by controlling the rise time wJ (change) of the laser power, the width of the line in the sub-scanning direction can be changed to an arbitrary width. Also good. The laser power rise time is the time it takes for the laser power to reach the actual light emission level from the reference bias.

In addition, the time constant of the CR time constant circuit in the laser lighting time control section was changed by changing the resistance value of the variable resistor in the CR time constant circuit during device manufacturing, but this is not limited to this. The changeover signal from an external device (external host computer) or the changeover switch inside the device (
It may also be changed by a switch.

In this case, the line width within one image can be changed.

In addition, although we have described the case where the width of the line (vertical line) in the sub-scanning direction is controlled, the width of the line (vertical line) in the main-scanning direction is not limited to this, and by changing the setting value (setting level) of the beam light amount setting section, It is also possible to add something that controls the width of the horizontal line (horizontal line). Even if this setting value is changed during manufacturing,
It may be changed by a switching signal from an external cutter (external host computer) or a changeover switch (ditub switch) within the device.

[Effects of the Invention] As detailed above, according to the present invention, the line width in the direction perpendicular to the main scanning direction can be controlled and can be made arbitrary, and the line width in the n1 scanning direction can be controlled. Accordingly, it is possible to provide an image forming apparatus that can change only the line width in the main scanning direction without affecting the line width.

[Brief explanation of the drawing]

FIG. 1 to FIG. 6 show an embodiment of this invention.
FIG. 1 is a block diagram schematically showing the configuration of the laser drive circuit, FIG. 2 is a cross-sectional view illustrating the overall configuration of the laser printer, and FIG. 3 is the laser lighting time tII110.
Figure 4 is a diagram schematically showing the configuration of the parts; Figure 4 is a diagram for explaining the output waveform of each part in Figure 3; Figure 5 is a diagram for explaining the relationship between the laser beam intensity distribution and image characteristics; 6
The figure is a diagram for explaining image data, laser light output, and an image after development and fixing, and FIG. 7 is a block diagram schematically showing the configuration of a laser drive circuit for explaining another embodiment. Figure 8 shows the laser transient output 1 in Figure 7.
FIG. 9 is a diagram schematically showing the configuration of the 11111 section. FIG. 9 is a diagram for explaining the image data, transient output, and image after development and fixing in FIG. 7. FIG. 10 is a diagram showing the laser scanning system of the laser printer. It is a perspective view for explaining. 11... semiconductor laser (laser light emitting means), 13...
...Polygon mirror, 17...Photosensitive drum, 46.
... Laser drive unit, 48... Laser lighting time control unit, 5o... External device, 51-54... NAND circuit, 57... CR time constant circuit. Applicant's representative Patent attorney Takehiko Suzue 11 Figure 3 Figure 4 Figure 1 Ji 7 Figure 9 Figure 10 Procedural amendments Showa year 62 φ 2 Kame Commissioner of the Patent Office Black 1) Akio Tono 1, Case indication patent application Showa No. 61-122567 No. 2, Name of the invention Image forming device 3, Relationship to the amended case Patent applicant (307) Toshiba Corporation 4, Agent UBE Building, 3-7-2 Kasumigaseki, Chiyoda-ku, Tokyo; −
3;'08 7, Contents of amendment (1) In the 11th page, line 12 of the specification, and the 18th line of the cylinder on the same page, the words "2μS/protection" were replaced with [2μJ/ml]
I am corrected. (2) In the third line of page 4 of the specification, and from the third line to the fourth line of page 19, "line width in the direction perpendicular to the main scanning direction" is replaced with "line width in the direction perpendicular to the main scanning direction". Correct it to ``line width''.

Claims (1)

[Scope of Claims] Laser light emitting means for emitting laser light in accordance with image data; scanning means for deflecting and scanning the laser light from the laser light emitting means; an image forming device for forming a dot-like latent image on the photoreceptor; An image forming apparatus comprising: control means for changing a period during which the laser beam is emitted in accordance with a scanning period specified by a specifying means.