JPS6125165A - Printing device - Google Patents

Abstract

PURPOSE:To obtain excellent print quality by varying the light emission intensity of a light emission source by an intensity control pat according to specified resolution, and varying an apparent spot diameter and setting an optical spot diameter within a constant range. CONSTITUTION:When an intensity specifying signal SD indicates that a high resolution mode is off, a transistor (TR) Q1 turns off and a modulated signal LEDS, on the other hand, is inputted to a modulating circuit 210 to drive a laser diode 12a with a driving current obtained by superposing the modulated signal upon a bias current ic. Namely, the potential is raised almost to a threshold value T with the bias current ic and the diode is driven with the current having the modulated signl LEDS superposed thereupon. When the optical spot diameter is set within the range shown by an expression, a sufficient voltage margin is obtained even if the intensity is varied by switching the resolution, and excellent print quality is obtained even if a photosensitive body varies in potential. Bleeding due to a scatter is minimized at such an electrostatic charging potential at which the print density is small, and large with high print density and small with low resolution, but when the resolutio is low, unit line width is large and there is no apparent variation.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a printing device such as an electrophotographic printer that forms a latent image on a photoconductor by exposure to spot light from a light emitting source. The present invention relates to a printing device that can change the diameter of a unit printing pixel by changing the diameter of a unit printing pixel, and particularly relates to a printing device that can change the diameter of a printing pixel by changing the emission intensity without changing the optical spot diameter of a light emitting source.

2. Description of the Related Art Electrophotographic printing devices are widely used because they can print on plain paper and can print various patterns. In such a printing apparatus, a laser light source is used as an exposure source, and is constructed as shown in the overall configuration diagram in FIG. 15 and the optical system configuration diagram in FIG. 16.

That is, a photosensitive drum 4 having a photoconductor (photoreceptor) on its surface.
A charging device 5, a developing device 6, a transfer device 7, a static eliminating unit 8, and a cleaner 9 are arranged around the electrophotographic unit, and a laser diode 12, a collimating lens 13, a polygon mirror 14, and an F-θ (image forming ) Lens 1
6. The mirror 17 constitutes an illumination optical unit,
Furthermore, a paper handling unit is constituted by a paper hopper 1, a feed roller 2, a conveyance roller 3, a fixing port mirror 10, and a stun force 11. In such a printing device, a laser beam modulated according to a written image from a laser diode 12 as a laser source is optically scanned by a polygon mirror 14 rotated by a spindle motor (servo motor) 15 via a collimating lens 13. and F-θ lens 1
6. The photosensitive drum 4 charged by the charger 5 is exposed to a hesitating light through the mirror 17. As a result, a latent image is formed on the photosensitive drum 4, which is developed by the developing device 6. The developed image is transferred by the transfer device 7 onto the paper CP, which is fed out from the paper hopper 1 by the feeding roller 2 and sent to the transfer section by the conveyance roller 3. transcribe and set. Thereafter, the paper cp is fixed by the fixing device 10,
The photosensitive drum 4 is housed in a stacker 11, while the photosensitive drum 4 is neutralized by a static eliminating unit 8, cleaned by a cleaner 9, and used for the next latent image formation.

In such a laser printing apparatus, as shown in FIG. 16, a laser source 12, a polygon mirror (scanning mirror) 14, and a spindle motor 15 are provided as an optical system. An image is formed by scanning the photosensitive drum 4 rotated by the motor 4a in the X direction of FIG. 17(A), that is, in the main scanning direction. This laser source 12 is driven by a modulation signal LEDS according to the written image, and the laser source 12 is driven by a modulation signal LEDS corresponding to the written image. Since a light dot train corresponding to the modulation signal LEDS is generated from s12, a written image is formed on the photosensitive drum 4.

Therefore, as shown in FIG. 17(A), the spot diameters of the beams of the laser source 12 are set so that they overlap each other at positions X1 to Xm on each main scanning line, and the rotation of the drum 4 performs sub-scanning Yl-Yn. .

A latent image is formed on the photosensitive drum 4 by the spot light from the laser source 12 in the following manner. For example, as shown in FIG. 17(B), when the modulation signal is on, off, and on, spot light S1 is irradiated at position XI and spot light S3 is irradiated at position X3. When the threshold value of T is assumed to be T, the charge in the portion above the threshold T disappears, and a latent image 31 is formed as shown in the figure. When performing normal development, a visible image like DI can be obtained by applying toner with a polarity opposite (minus) to the charging potential VC. That is, the part where the modulation signal is off becomes a black pattern, and the unit line width (pixel diameter) becomes d.

In such a printing device, the unit line width d depends on the spot diameter and is constant. However, there is a need or desire to change the unit line width.

For example, when changing the resolution as shown in FIG. 18, it is necessary to change the unit line width from dl to dl. That is,
In the case of high resolution (for example, 400 dpi), the dot spacing in the main scanning direction is as small as dbl, and the dot spacing (linear density) in the sub-scanning direction is correspondingly small as dbl, but in the case of low resolution (for example, 300 dpi), In this case, the dot spacing in the main scanning direction is large, db2, and the dot spacing in the sub-scanning direction is correspondingly large, db2. For this reason, it is necessary to set the unit line width to dl- at high resolution, and to set the unit line width to dl at low resolution.

[Conventional technology]

Conventionally, in order to adjust the line width as described above, a method is known in which the optical spot diameter of the light beam is expanded to change the line width from dl to dl. For this reason, conventional methods have been proposed to change the spot diameter by providing a plurality of laser sources (light emitting sources) with different spot diameters or by changing the focal length by moving the optical system.

On the other hand, a method is also known in which the modulation width in the main scanning direction is changed and the line width is adjusted using an oval beam.

[Problem that the invention seeks to solve]

The former conventional method described above has the problem that it requires an extra laser source and a complicated optical system, making the device itself complicated and expensive. Further, although the latter method allows adjustment in the main scanning direction, the spot diameter does not change in the sub-scanning direction and line width adjustment in the sub-scanning direction cannot be performed, so there is a problem that fine lines cannot be resolved.

[Means for solving problems]

SUMMARY OF THE INVENTION An object of the present invention is to provide a printing device in which one light emitting source is electrically controlled to change the line width according to the resolution and to obtain the maximum operating margin at each resolution.

Therefore, the present invention provides a photoreceptor, a charger that charges the photoreceptor, a light emitting source that writes an image on the photoreceptor with a predetermined spot diameter, and an intensity control section that controls the emission intensity of the light emitting source. The intensity control section changes the light emission intensity of the light emitting source according to the specified resolution to change the apparent spot diameter to obtain a printing pixel diameter corresponding to the resolution, and the light emitting source. The optical spot radius of 1. io ・(PIIlin +
Pn+ax )/2 to 1.40 ・(P+nin
+P+cax)/2.

[Effect]

In the present invention, printing illumination corresponding to a specified resolution is achieved by changing the apparent spot diameter by controlling the emission intensity of the light source.
In addition to obtaining the prime diameter, the operating margin at each resolution,
That is, the optical spot diameter is determined so that the range of charging potential that provides good print quality is maximized.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

Figure 2 is a diagram of the principle of line width adjustment, Figure 3 is a diagram of line width adjustment characteristics,
FIG. 4 is an explanatory diagram of line width adjustment.

First, the principle of line width adjustment will be explained with reference to FIGS. 2 and 3.

As shown in the intensity level distribution diagram of the light beam in FIG. 2 (Δ), if the optical spot diameter of the light beam L1 with intensity P1 is 1], the apparent spot diameter as seen from the photoreceptor is This is Dl for the portion above the threshold T. Here, the optical spot diameter is 1/e2 of the intensity PI, that is, 0.1
3・P+. On the other hand, when the optical spot diameter D, that is, the focal length is the same, and the intensity level is increased as shown in P2, the light beam L2 becomes similar to the light beam L1 as shown in the figure, and the optical spot diameter is the same as D. However, the apparent spot diameter is D larger than the threshold T of the photoreceptor.
2 and spread.

Therefore, as shown in FIG. 2(B), a light beam L2 of intensity P2
When irradiated in the same manner as in FIG. 17(B), the apparent spot diameter is enlarged, so that the unit line width of the latent image S■ and the developed visible image becomes smaller.

In this way, by changing the intensity of the light beam, you can create an apparent SuboyH'! - to adjust the line width.

That is, since the amount of laser light and the line width are inversely proportional as shown in FIG. 3, in order to obtain the desired line width, it is sufficient to drive the laser source 12 with the corresponding amount (intensity) of the laser light.

Therefore, in order to change the line width according to the resolution, for high resolution, a light beam with a small laser intensity like Pl is used as shown in Figure 4 (A), and for low resolution, as shown in Figure 4 (B). If the intensity is changed according to the resolution so that the laser intensity becomes a large light beam as shown in P2, the corresponding unit line width d
+, d2 will be obtained.

In this way, in the present invention, the line width is adjusted by changing the intensity without changing the optical spot diameter, but the optical spot diameter remains the standard. Therefore, the operating margin width is determined by setting the optical spot diameter.

In the present invention, the optical spot diameter that maximizes the operating margin width when the intensity changes is obtained as follows.

FIG. 5 is a characteristic diagram of the optical spot diameter and drum surface potential, showing the range of surface potential of the photosensitive drum in which good printing quality can be achieved with respect to the optical spot diameter.

The inventors have determined that each laser beam diameter (optical spot diameter)
The drum surface potential at which good quality could be obtained was measured by varying the intensity of the light beam when the resolution was 200 dpj (dots per inch) and 300 dpi. For this measurement, good quality includes no smudging (dust),
In addition, the range in which horizontal line omission did not occur was determined by visually checking the printing results.

Missing horizontal lines means that in Fig. 17, when scanning lines Y1 and Y3 are scanned with an optical vino, the horizontal lines that would otherwise appear on scanning line Y2 are missing and cannot be seen, and in this case, the spot diameter of the tool This is because it is too large. On the other hand, dust is a phenomenon that occurs when the charged (surface) potential is too high compared to the light beam intensity.

For example, when the optical spot diameter was set to 90 μm, at 300 dpi, dust appeared when the surface potential was about 950 V or more, and horizontal line omission occurred when the surface potential was about 650 V or less. Similarly, at 200 dpi, dust appeared when the surface potential was about 800 V or more, and missing horizontal lines occurred when the surface potential was about 650 V or less.

In this way, similar measurements were made for each optical beam diameter, and the characteristics shown in FIG. 5 were obtained. In addition, the surface potential is about 10
At 50 V or more, fogging occurred, and at about 550 V or less, the printing density was too low and good results could not be obtained. As can be seen from this characteristic, the optical spot diameter at which the potential margin is maximum at high resolution (300 dpi) is different from the optical spot diameter at which the potential margin is maximum at low resolution (200 dpi). Therefore, it is necessary to set an optical spot diameter that provides the maximum potential margin in both side image degrees.

If we rewrite this FIG. 5 and take the ratio r of the optical spot radius to the resolution expressed by the following equation on the horizontal axis, we get something like FIG. 6.

Pm1n +Pmax However, Pm1n is the scanning pinch at the minimum resolution (db1 in FIG. 18(A)), and Pmax is the scanning pitch at the maximum resolution (db2 in FIG. 18(B)).

Here, a is the characteristic at the maximum resolution (300 dpi), and b is the characteristic at the minimum resolution (200 dpi).

Examining FIG. 6, at r-1,0 indicated by ■, an operating voltage range of 400 volts or more is obtained at high resolution, but an operating voltage range of only 200 volts is obtained at low resolution, and the photoreceptor Due to potential fluctuations, blurring and missing horizontal lines occur at low resolution. Conversely, r=1.
5 provides an operating voltage range of over 400 volts at low resolution, but
Only Porto can provide an operating voltage range, and fluctuations in the potential of the photoreceptor can cause blurring and missing horizontal lines at high resolution.

On the other hand, considering potential fluctuations of the photoreceptor, it is sufficient to obtain an operating range of 300 volts, so r −1,10
The range shown by ■ from ~1.40 is optimal.

In other words, by transforming Equation (1), the optical spout/throat radius to be found is as follows, so it can be set as follows.

By setting the optical spot diameter within this range,
Even if the intensity is changed by switching the resolution, a sufficient voltage margin can be obtained, and good print quality can be obtained even if the potential fluctuation of the photoreceptor occurs.

The setting of this optical laser beam diameter is shown in Figs. 15 and 16.
The distance between the photosensitive drum 4 and the collimating lens I3 is changed and set by adjusting the position of the collimating lens 13 shown in the figure.

In this way, when the optical spot diameter is set, 20
The radar power ratio between 0dpi and 300dpi is
As shown in FIG. 7, for example, when D=140 μm, by setting the laser power ratio to 114%, the optimum line width can be obtained according to resolution switching.

Next, specific examples of the present invention will be described.

FIG. 1 is a configuration diagram of one embodiment of the present invention, and in the figure, the 15th
Components that are the same as those shown in the figures and FIG.
21 is a laser drive circuit (intensity control unit) that drives the laser source 12 with the intensity according to an intensity designation signal SD, which will be described later, according to a modulation signal (video signal) LEDS. Reference numeral 22 is a mork drive unit which drives the morph 15 at a speed according to the speed designation signal VD.
23 is a control unit which drives a strength designation signal SD corresponding to a resolution switching signal DS given from the outside;
A charging control unit 24 generates a charging voltage designation signal ST and a speed designation signal VD, and a charging voltage designation signal ST is given from the control unit 23 in response to resolution switching as described later.
Accordingly, a control voltage Vc is generated to control the charging strength of the charger 5.

Next, the operation of the embodiment configuration in FIG. 1 will be explained. In response to the high resolution designation signal DS, the control section 23 issues the strength designation signal SD, charge voltage designation signal ST, and speed designation signal VD corresponding to the high resolution. , the laser drive circuit 21 drives the light emitting source 12 according to the modulation signal LEDS with a beam intensity P+ for high resolution (FIGS. 2 and 4 (A)), and the motor drive section 22 drives the spindle motor 15 at a high resolution speed. The polygon mirror 14 is driven to rotate at a certain speed, and the light emitting source 12 is rotated at a predetermined optical scanning (main scanning) speed.
scan the laser beam.

That is, the unit line width is set to di corresponding to high resolution,
Writing is performed by the light emitting source 12.

Next, when the resolution designation signal DS is switched to low resolution, the control unit 23 switches the strength designation signal SL) corresponding to the low resolution,
A charging voltage designation signal ST and a speed t-setting signal VD are generated.

Thereby, the laser drive circuit 21 drives the light emitting source 12 according to the modulation signal LEDS with a beam intensity P2 for low resolution as shown in FIGS. 2 and 4(B). At this time, the period of the modulation signal LEDS (successive clock) is also shown in Fig. 18 (B).
db2 is longer for low resolution and reaches the laser drive circuit 21.

On the other hand, the motor drive section 22 switches the speed to a low resolution speed, drives the spindle motor 15, rotates the polygon mirror 14 at the speed, and scans the laser beam from the light emitting source 12 at the low resolution optical scanning speed. do.

That is, the resolution in the sub-scanning direction is determined by the rotation speed (sub-scanning speed) of the photosensitive drum 4, but in this example, the resolution in the sub-scanning direction is determined by changing the main scanning speed of the polygon mirror 14 without changing the rotational speed of the photosensitive drum. The rotation speed of is changed equivalently.

Therefore, the unit line width d2 is set according to the low resolution,
Writing is performed by the light emitting source 12.

The operation of the charging control section 24 based on the charging voltage designation signal ST will be described later.

Next, the laser drive circuit configured in FIG. 1 will be described in detail.

FIG. 8 is a detailed circuit diagram of the laser drive circuit 21 having the configuration of the embodiment shown in FIG. 1. In the figure, the same parts as shown in FIG. 12b is a monitor diode that receives the light from the laser diode 12a and converts it into an electric signal. 210 is a modulation circuit that performs switching operation according to the modulation signal LEDS and changes the drive current. 211 is an amplifier that amplifies the output current of the monitor diode 12b, 212 is a gain change circuit that changes the feedback gain according to the strength designation signal sD, and resistors R1 and R2. 213 is a comparison path consisting of the transistor Q1, which compares the feedback signal from the gain change circuit 212 and the modulation signal LEDS, and outputs the signal from the laser diode 12.
This is to change the bias current ic flowing through a.

Next, the operation of the embodiment configuration shown in FIG. 8 will be explained with reference to the waveform diagram in FIG. 9 and the laser diode drive explanatory diagram in FIG. 1O.

First, if the intensity designation signal SD is off (high resolution),
Transistor Q1 is off. On the other hand, the modulation signal LED
S is connected to the modulation circuit 210, and the laser diode)' I
2a is driven with a drive current obtained by adding a modulation signal to the bias current ic. As shown in FIG. 10, the characteristics of the laser diode are non-linear in terms of the drive current versus the amount of laser light. Therefore, the bias current i (with threshold T
It is brought to the vicinity and driven by adding a modulation signal LEDS to it.

In addition, in order to keep the laser power constant, the light emitting state is monitored by the monitor diode 12b, and the feed hack signal is subjected to a feed hack via the amplifier 211 and the gain change circuit 212, and the modulation signal LEDS and the feed hack signal FS are compared by the comparison circuit 213. The laser power is controlled to be constant by controlling the bias current IC.

On the other hand, when SD is turned on (low resolution) and the line width (intensity) specification changes, transistor Q1 is turned on and the voltage is divided by resistor R2, so the gain decreases and therefore the feed hack signal from monitor diode 12b is The level of FS decreases. Therefore, the comparator circuit 213 uses the modulated signal L
When compared with EDS, it is assumed that the laser power has decreased by this level reduction, and the bias current is increased like IC. As a result, the laser power (light amount) is P
The light intensity increases from l to R2, the emission intensity increases, the apparent spot diameter is expanded, and the line width is set to d2 for low resolution.

Next, the operation of the charging control section 24 will be explained with reference to FIG. 11, which is an explanatory diagram of overexposure phenomenon, FIG. 12, which is a density characteristic diagram, and FIG. 13, which is an explanatory diagram of charging potential control.

First, we will explain the bleeding phenomenon due to overexposure by referring to FIG.
As shown in A), a rectangular potential distribution with a clear border between the exposed area and This causes a kind of Haleshigon phenomenon.As a result, as shown in FIG. 11(B), the potential in the non-exposed part flows into the exposed part at the potential between the exposed part and the non-exposed part, and this part The image appears as a splatter and smudge.

For this reason, when the laser power is increased, the image quality deteriorates.

On the other hand, as shown in FIG. 12, the relationship between the charging potential and the printing density is such that the increase in the charging potential is proportional to the increase in the printing density.

Therefore, in the present invention, when the amount of laser light is large (low resolution), the charged potential is reduced as shown by vL in FIG.
In other words, the higher the print density, the more likely it is to smear. Therefore, if the charging potential is set to a low print density, the smearing caused by the aforementioned scattering will be minimized, and in the end it will be possible to minimize the smearing. can. In this case, the print density is large at high resolution and small at low resolution, but as described above, the unit line width is large at low resolution, so the appearance remains unchanged.

Therefore, when the control unit 23 designates the laser intensity as high, it designates the charging voltage designation signal ST as low, and when the laser intensity is designated as low, it designates the charging voltage designation signal ST as high. As a result, the charging control section 24 changes the control voltage Vc, controls the charging voltage of the high voltage power supply 2o, and controls the charging voltage of the photosensitive drum 4.
The upper charging potential is set to vH (low laser elongation, high resolution) or vL (large laser intensity, low resolution) in FIG. 13 according to the laser intensity.

FIG. 14 is a detailed circuit diagram of the charging control section 24 having the configuration of the embodiment shown in FIG. 1. In the figure, the same parts as those shown in FIG. 241 is a Hee-Sumi pressure generation circuit that generates a base voltage (Vc+ +yc2) for low resolution, and R3 , R4 is its output resistance, 242
is an additional voltage applying circuit, which includes resistors R1 and R2 and a transistor QTI. When the charging designation signal ST is off (high resolution), the transistor QTI is turned off, and the resistor R+
, R2, an additional voltage Vc3 is generated from the midpoint of R2.

Next, the operation of the embodiment configuration shown in FIG. 14 will be explained.

When the charged voltage designation signal ST is on (low resolution), the transistor QTI is on, so the additional voltage generation circuit 24
Since no additional voltage is generated from the adder 240, the control voltage Vc that is the output of the adder 240 becomes the base voltage (Vt; ++Vc2), and the high-voltage power supply 20 generates a corresponding charging voltage to change the charging potential of the photoreceptor 4 to the second level. Let it be vL in Figure 13.

On the other hand, when the charged voltage designation signal ST is off (high resolution), the transistor QTI is off, so the additional voltage generation circuit 242 generates the additional voltage Vc3, and the adder 240
The control voltage Vc, which is the output of the base voltage (Vc++Vc
2) and the additional voltage Vc3, a corresponding charging voltage is ordered from the high-voltage power supply 20, and the charging potential of the photoreceptor 4 is set to VH in FIG. 13(B).

In this way, an image with less blur can be obtained even if the laser power is increased to adjust the line width.

In the above-mentioned embodiment, a laser diode is used as a light emitting source, but the light source is not limited to this, and any type that can have variable intensity may be used, and the optical scanning system is not limited to that in the embodiment.

Although the present invention has been described above using one embodiment, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a photoreceptor, a charger that charges the photoreceptor, a light emitting source that writes an image on the photoreceptor with a predetermined spot diameter, and control of the light emission intensity of the light emitting source. The intensity control section changes the light emission intensity of the light emitting source according to the specified resolution, changes the apparent spot diameter, and adjusts the print pixel diameter corresponding to the resolution. At the same time, the optical spot diameter of the light emitting source is set to 1.10·(P
min + Rmax > / 2 to 1.40 ・
Since the line width is set within the range of (Pm1n + Pmax)/2, the line width can be changed in response to resolution switching by electrically controlling one light emitting source, so the device configuration can be changed. In addition to being simple and inexpensive, it is also possible to easily obtain a desired line width.

In addition, by setting the optical spot diameter within a certain range, even if the apparent spot diameter changes due to resolution switching, the maximum voltage margin can be obtained. Even if the charging potential varies, good printing results can be obtained at any resolution, and this greatly contributes to the spread of printing apparatuses that perform such resolution switching.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a diagram of the line width adjustment principle of the present invention, Fig. 3 is a diagram of laser light amount vs. line width characteristics, and Fig. 4 is a diagram of the line width adjustment principle of the present invention.
The figure is an explanatory diagram of line width adjustment according to the present invention, Figure 5 is an optical spot diameter versus photosensitive drum surface potential characteristic diagram, Figure 6 is an optical spot diameter ratio versus operating voltage characteristic diagram, and Figure 7 is an optical spot diameter characteristic diagram. Figure 8 is a detailed configuration diagram of the laser drive circuit in the configuration shown in Figure 1, Figure 9 is a waveform diagram of each part in the configuration shown in Figure 8, and Figure 10 is a characteristic diagram of the laser diode in the configuration shown in Figure 8. , Fig. 11 is an explanatory diagram of the bleeding phenomenon caused by overexposure, Fig. 12 is a graph of charging potential versus printing density characteristics, and Fig. 13
14 is a detailed configuration diagram of the charging control section in the embodiment configuration of FIG. 1.
FIG. 5 is a configuration diagram of an example of a printing device to which the present invention is applied.
6 is a detailed configuration diagram of the optical system of the configuration shown in FIG. 15, FIG. 17 is a diagram illustrating the recording principle in electrophotography, and FIG. 18 is a diagram illustrating the necessity of line width adjustment. In the figure, 4-photosensitive drum (photosensitive member), 5-charger, ]2-
Light source, 14-polygon mirror, 15-spindle-
20-high voltage power supply, 21-rape drive circuit (strength control section), 22-motor drive section, 23-control section, 24-
Charge control section.

Claims (1)

[Claims] It has a photoreceptor, a charger that charges the photoreceptor, a light emitting source that writes an image on the photoreceptor with a predetermined spot diameter, and an intensity control section that controls the emission intensity of the light emitting source, and has a specified The intensity control unit changes the light emission intensity of the light source according to the resolution, changes the apparent spot diameter, obtains a print pixel diameter corresponding to the resolution, and changes the optical spot diameter D of the light source. , scanning pitch P at the lowest resolution of the specified resolution
min, 1 for the scanning pitch Pmax at the highest resolution
．． 10・(Pmin+Pmax)/2 to 1.40・(
A printing device characterized in that the setting is within the range of Pmin+Pmax)/2.