JPH04185360A - Recording device - Google Patents

Abstract

PURPOSE:To ensure that a high-quality image can be recorded by detecting a specified relationship between a non-exposed dot and an exposed dot, and controlling the quantity of light of a light beam based on the detection results. CONSTITUTION:If it is interpreted that a pixel 3C is an isolated black dot using a specified algorithm, a signal 19 which increases a laser output is sent to a laser drive circuit 16. If it is interpreted that the pixel 3C is an isolated black dot adjacent to a white dot, a signal which decreases the laser output is sent to the laser drive circuit 16. In addition, it is interpreted that neither of the above cases is applicable, a signal 20 which moderates the laser output is sent to the laser drive circuit 16. The laser drive cirucit 16 drives under control the laser beam 25 so that data is printed at a specified laser output in accordance with control signals 19 to 21 and VIDEO signal 22. In addition, the drive current IF of a semi-control laser and an optical output strength PO are related to the other as illustrated, and therefore, an optical output strength complying with drive current variations can be obtained, if the drive current are varied.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image recording device, for example, a laser beam printer, an LED printer, etc., which scans a spot-shaped light beam on a recording medium based on image information. The present invention relates to a recording device that records images.

[Prior Art] FIG. 9 is a diagram illustrating the image forming operation of a conventional laser beam printer, where lot is an image signal (VIDEO) that is input to the laser unit 102.

103 is a laser beam that is modulated on and off by the laser unit 102, and 104 is a motor that rotates a rotating polygon mirror 105 at a constant speed.

106 is an imaging lens, and the deflected laser beam 107
is focused on the photosensitive drum 108. therefore,
The laser beam 103 modulated by the image signal 101 horizontally scans the photosensitive drum 108 (scanning in the main scanning direction).
be done. 109 is a beam detector, and a photoelectric conversion element 110
, for example, has a photodiode, and has a Rokuhei synchronization signal (hereinafter referred to as BD) 11 that is the image writing timing.
Outputs 1. 11.2 is a transfer paper, and a photosensitive drum 108
A developing device (not shown) visualizes the latent image formed on the toner image, and a toner image is transferred by a transfer device (not shown).

Next, the principle of image formation in the above-described apparatus will be explained in the case of an image exposure method in which an exposed portion exposed to a light beam is visualized.

FIG. 10 is a diagram schematically showing the relationship between the potential on the photosensitive drum and the formed image. ■ In the same figure. is the potential of the non-exposed area, ■ is the potential of the exposed area, and ■. , is the developing bias. As shown in the figure, the potential of the portion of the photosensitive drum exposed by the laser beam decreases from vl to vL. On the other hand, for toner, the potential on the drum is development bias■. . Since it adheres to the area lower than the developing bias V. By setting the potential of e to a value between the exposed part potential vL and the non-exposed part potential (2), an image is formed with the exposed part as "black" and the non-exposed part as "white".

[Problems to be Solved by the Invention] In recent years, laser beam printers have become increasingly high-definition, and some have a resolution of 600 dpi (dots/inch) or higher. If you try to obtain the same print speed as the currently mainstream 300 dpi printer with such a high resolution printer, the scanning speed of the laser beam will increase if you use the same optical system.

Especially when printing isolated dots, problems arise due to the exposure amount distribution on the photosensitive drum depending on the beam spot diameter, laser lighting time per dot, etc.

This will be explained with reference to FIG.

Figure 11 (a) schematically shows the potential distribution on the drum when one isolated black dot is printed in a white image, and (b) shows the potential distribution on the drum when one isolated white dot is printed in a black image. FIG. In the figure (a), when a black isolated dot is placed in a white image, it is shown that the potential of the exposed area does not completely fall to 2 with respect to the potential v0 of the non-exposed area. The reason for this is that on a 600 dpi machine, compared to a 300 dpi machine, the length of one dot in the main scanning direction is longer, and the scanning speed of the laser beam is twice as long, so the laser lighting time is dependent on the length of one dot. The amount of exposure per area is reduced. Further, since the spot diameter of the laser beam is adjusted to 300 dpi, the light amount distribution is wide, and the light energy per unit area required to lower the potential on the drum to vL cannot be obtained.

On the other hand, in FIG. 11(b), when a white isolated dot is placed in a black image, the laser off time is longer than in the 300 dpi machine for the reason explained above. In the surrounding black pixels, the spot diameter of the laser beam is large, so the area of the unexposed part becomes very small.
The potential is also influenced by the surroundings and becomes the potential of the non-exposed area, V. The value will be lower than .

In the potential distribution as explained above, if the developing bias voltage is set to VDCI, isolated black dots can be reproduced, but isolated white dots cannot be reproduced.
When the developing bias potential is set to VDCI, on the other hand, white dots appear but black dots do not appear.

The above problem can be solved by changing the laser beam spot diameter to 600 mm.
This can be solved by making it smaller to match the dpi, but in that case, the optical system would require extremely strict mechanical precision to maintain a good image, which would increase costs. The focal length of the optical system is long (which also causes the printer itself to become larger).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a recording device that solves the above-mentioned problems.

[Means for Solving the Problem] In order to achieve the above object, the present invention scans a recording medium with a light beam consisting of non-exposed dots and exposed dots corresponding to image information to record an image on the recording medium. A recording device that stores the image information for at least three scanning lines in the sub-scanning direction; and a recording device that stores the image information for at least three scanning lines in the sub-scanning direction; The present invention is characterized in that it comprises a detection means for detecting a non-exposed dot existing isolated among exposed dots, and a control means for controlling the amount of light of the light beam based on the detection result of the detection means.

[Function] According to the present invention, a high-quality image is recorded by detecting a predetermined relationship between unexposed dots and exposed dots and controlling the amount of light beam based on the detection result.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

<Embodiment 1> FIG. 1 is a block diagram showing the vicinity of a laser drive circuit of a laser beam printer that is an embodiment of the present invention.

In the figure, line memories 1 to 6 each store one line of image data in the main scanning direction. 7 is a demultiplexer, which is sent from a controller (not shown).
Writing of the image data signal 18 for each main scan into one of the line memories 1 to 6 is specified by the value of a line counter 15, which will be described later. 8 is a data selector that selects five outputs from the six data, 10 to 14 are shift registers, 9 is a logic gate circuit, and 16 is a drive circuit that drives the semiconductor laser 25.

Next, the image forming operation in this embodiment will be explained below with reference to FIG.

A controller (not shown) that generates the image data signal 18 sequentially sends out the image data signal 18 for one line in the main scanning direction in synchronization with the horizontal synchronization signal (BD scratch signal 24). One line of image data 18 sequentially sent to is written into one of the line memories 1 to 6 designated by the demultiplexer 7 in accordance with the value of the line counter 15 counted by the BD signal 24. It can be done.

On the other hand, from the line memories 1 to 6 to which writing has not been performed, only the reading ratio of image data for five lines that have already been written is performed simultaneously with the above-mentioned writing operation. The five lines of read image data are stored in shift registers 10 to 10 in order from the data written first by the data selector 8 controlled by the line counter 15.
14 respectively. The shift register lO~
The image information of "24 pixels" surrounding the irradiated pixel 23 outputted from the irradiation pixel 23 is subjected to a predetermined logical operation by the logic gate circuit 9 based on an algorithm described later, and the image information is outputted from the control signal 19 to control the output of the semiconductor laser 25. 21 to the laser drive circuit 16. In addition, the irradiation pixel 23
The image data is sent to the laser drive circuit 16 as a VIDEO signal 22. The laser drive circuit 16 controls and drives the laser 25 according to the control signals 19 to 21 and the VIDEO signal 22 described above.

Note that writing to the line memories 1 to 6 and outputting to the shift registers 10 to 14 are performed in synchronization with the image clock signal 26 that controls the timing of each pixel.

Next, an isolated dot is detected in the logic gate circuit 9,
An algorithm for controlling the strength of the laser output will be explained below with reference to FIG.

As shown in FIG. 2(A), the irradiated pixel is named 30. Then, the pixel 1 dot before the irradiation pixel 3C on the same line is 3B, the pixel 1 dot before is 3A, the pixel 1 dot after the irradiation pixel 3C is 3D, and the pixel 1 dot after is 3B. Name it 3E.

Also, the pixel at the same position as 30 before l scanning is set to 2C, and 2
The pixel one dot before C is 2B, the pixel one dot before C is 2, the pixel one dot after 2C is 2D, and the pixel one dot after 2E is 2E. Similarly, 3A, 3B, 3G, 3D, 3E on the line two scans before the pixel 3C
The pixels at the same position as IA, IB, 1. C
, L.D. IE 4. Pixels on the line after one scan and two scans of the relevant pixel 3C. A, 4B, 4G, 4D
, 4E and 5A, 5B, 5G, 5D, 5E.

FIGS. 2(a) to 2(i) are diagrams illustrating an algorithm for determining black or white isolated dots. In the figure, dots shown in black are black dots, dots shown in white are white dots, and dots shown with diagonal lines indicate that they can be either black or white. (a) is a condition for determining that the pixel 3C is an isolated black dot. That is, when the pixel 3G is a black dot and all the surrounding dots are white dots, the pixel 3C can be considered to be an isolated black dot. This can be written as a logical formula: 3(j2B books 2C*2D books 3B*3D$4B$4CID
=1...(1). However, the symbols represent image information of each dot, and those with "1" attached to the symbol indicate white dots, and those without "1" indicate black dots.

Next, (b) to (i) are conditions for determining that the pixel 3C is a black dot adjacent to an isolated white dot. This is a condition that there is a white dot adjacent to the pixel 3C, and all dots adjacent to the white dot are black dots, and if any one of (b) to (i) is satisfied, the pixel 3C is 3C can be considered to be a black dot adjacent to an isolated white dot. If you write this as a logical formula, 3C monkey (2B umbrella IA * IBIIC umbrella 2A umbrella 2C umbrella 3A4)
3B+2CIIB book IC*ID*2B*2D*3B*3
D+2D Takashi IC umbrella ID*IE umbrella 2C12E*3D book 3E
+3B car 2A$2B umbrella 2C*3A*4A*4F3*4C
+3DI2C umbrella 2D umbrella 2E*3E*4Cne 4D medium 4E+
4B$3A 3B Umbrella 4A*4(:*5A*5B*5G+
4C*38*3D book 4Bne40*5B$5C book 5D+4
D*3D*3E umbrella 4 (:*4E*5C book 50*5E)=
1... (2).

If the algorithm described above determines that the pixel 3C is an isolated black dot, that is, the above (
1) Signal I9 that increases the laser output when the formula holds
In addition, if the pixel 3C is determined to be a black dot adjacent to an isolated white dot, that is, if the above formula (2) is satisfied, the signal 21 that weakens the laser output is further applied to any of the above. If the conditions do not apply, the laser drive circuit 16 sends the control signal 19 to the laser drive circuit 16 in FIG.
2l and the VIDEO signal 22, the laser 25 is controlled and driven so as to perform printing with a predetermined laser power. In this embodiment, the laser output is controlled by changing the laser drive current.

This is the driving current of the semiconductor laser, and the optical output intensity, P.
This is because, since the relationship of 0 is as shown in FIG. 3, by changing the drive current, it is possible to obtain a light output intensity corresponding to the change.

Next, FIG. 4 shows details of the laser drive circuit 16 in this embodiment. As shown in the figure, the image signal VIDEO 22 of the irradiated pixel 3C passes through a buffer 27 and then passes through a terminator resistor 28. 29 compensates the voltage level, and connects the switching transistor 31 via the base resistor 30.
is input. This transistor 31 becomes "ON" when the VIDEO signal 22 is "1", and conversely becomes "0".
It becomes “OFF”. Then, when the transistor 31 is turned on, the current of the constant current source constituted by the transistor 33 flows to the laser 25, and the laser 25 lights up. Furthermore, when the transistor 31 is off, the current (2) flows through the diode D1. As described above, the optical output of the laser 25 is determined by the value of the driving current I, and the value of the driving current I is the base potential v, l! of the transistor 33. This potential is determined by ■. By changing the current value, the value of the electric current can be controlled. The base potential (2) of the transistor 33 is given to the transistor 33 by impedance conversion of a voltage value v3 obtained by resistor division between V+ and V- by a voltage follower constituted by an operational amplifier 32. In this embodiment, the base voltage of the transistor 33, V, is 4
It is obtained by dividing the resistors R, , R, , R, , R4. That is, VR=V-+ (V--V-)fRz +R3+R4)
/ (R+ +R2+rt3+tt4)-- The laser 25 lights up at the current value I determined in (3).

Here, assuming that the emitter resistance of the transistor 33 is R6° and the voltage between the base and emitter is ■, the current I is (4
) is expressed by the formula.

I= (Vp-Vll!-V-) rtt
-(4) Analog switches 34 and 35 are connected in parallel to resistors R2 and R3, respectively,
The analog switches 34 and 35 each receive a control signal 2.
1.20 is turned on when it is “1” and turned off when it is “0”. That is, when the control signal 20 that specifies that the laser is being output is "1", the analog switch 35 is turned on and both ends of the resistor R3 are shorted, so the voltage 6 becomes VR=V-+(
V, -V-) (Rz+R4)/(R++R2+R4)
”・(5), and as a result, the value of the current ■ becomes small.

Further, when the control signal 21 that makes the laser output weak is "1", both the analog switches 34 and 35 are turned on, and v*=v-+ (V or -V-JR, / (R, +R,)
... (6), and the current I
The value of becomes even smaller.

As described above, the optical output of the laser 25 can be controlled by appropriately determining the values of the resistors R, , R, , R3, and R4.

FIG. 5 shows a schematic diagram of the potential on the drum when isolated dots are printed by controlling the laser output using the algorithm described above. FIG. 5A shows a case where black isolated dots are printed. In this case, since the laser output is set to be strong in the isolated black dot portion, the potential can be lowered to the exposed portion potential Vt. - Power cylinder 5 Figure (b) shows the case where a white isolated dot is printed, and in this case, the laser output of the adjacent black dots around the white dot is printed as weak, so there is no possibility that the white dots will be affected. Non-exposed part potential■,
can be kept. Therefore, the developing bias voltage vl
By setting llc between V and vL, it is possible to reproduce both isolated black dots and white dots.

In this embodiment, an example was explained in which the laser output is increased when an isolated black dot is struck (and the laser output for an adjacent black dot is weakened when an isolated white dot is struck), but for example, normally only an isolated white dot is Adjust it so that it can be reproduced,
If only isolated black dots are detected and the laser output is intensified in that case, there will be only three lines to refer to, and the logic can be simplified.

Furthermore, although the present embodiment has been described using a laser beam printer as an example, the present invention is not limited to this and can be applied to other electrophotographic recording devices such as an LED printer.

Furthermore, in the above embodiments, an image recording apparatus using an image exposure method in which a developer material adheres to a portion irradiated with a light beam has been described; however, the present invention is not limited to this. It can also be applied to an image recording device using a background exposure method in which a film is attached. In that case, the relationship between black dots and white dots in the above explanation is reversed.

<Embodiment 2> First, a second embodiment of the laser drive circuit according to the present invention will be described below with reference to the block diagram of FIG. 6.

In the figure, 36 is a constant current circuit that generates a constant current I,
37 and 38 are constant current switching circuits that flow a constant current 11112 in response to control signals 20 and 21, respectively.

In the above configuration, first, a case will be described in which the laser 8 power "strong" is specified. In this case, the control signal 20.
21 are both "0" and the constant current L++12 does not flow, so the current flows to the laser 25.

coincides with the current flow by the constant current circuit 36. here,
The switching circuit 39 is a circuit that switches the connection of the constant current circuit 36 depending on the input level of the input VIDEO signal 22. For example, while the VIDEO signal 22 is "1", a current IL is passed through the laser 25, and the VIDEO signal When 22 becomes "0", the current flows through the resistor R.

Next, when specifying "medium" laser output, control signal 2
0 is set to "1" and the control signal 21 is set to "0", a current 11 flows through the constant current switching circuit 37. On the other hand, since the current I from the constant current circuit 36 is constant, the laser 2
If the current flowing through 5 is IL, the following relationship holds true.

T=IL10it Therefore, the current ■ flowing through the laser 25 is given by the following formula,
can be reduced.

IL: I −i+ Furthermore, the control signal 21 specifying the laser output “weak” is “1”.
”, the constant current switching circuit 38 has lx>1+
The current 12 flows, and as a result, the current IL flowing through the laser 25 becomes as shown in the following equation and further decreases.

IL=IL −L As explained above, by controlling the drive current value of the laser 25, the laser output can be changed. According to this embodiment, the laser output can be changed more quickly and stably.

<Example 3> In the two examples described above, an example was shown in which the driving current of the laser 25 was changed to change the laser output in order to change the exposure amount of the photosensitive drum, but the pulse width of the driving current pulse of one dot was The exposure amount can also be changed by changing . In this embodiment, a case where the pulse width of the drive current as shown in FIG. 7 is controlled will be described below.

As shown in Figure 7, 40 and 41 are input VIDE
This is a delay circuit that delays the O signal 22 by a time t and outputs the delayed signal. The signal 44 is a signal obtained by delaying the VIDEO signal 22 of the irradiated pixel by a time 2t by the delay circuits 40 and 41, and the logical product ( AND
) is the signal 45. Similarly, signal 4
6 is the logical product (AND) of the VIDEO signal 22 and the signal 44.
).

FIG. 8 shows the timing of each of the signals 43 to 46 when the signal 22 is in the "1" state for one dot. As is clear from the figure, the signal 45 has a shorter pulse width by t than the signal 44, and similarly, the signal 46 has a shorter pulse width than the signal 44.
The pulse width is shorter by 2t compared to . and,
The data selector 42 to which the signals 44 to 46 having different pulse widths are input is configured to control the control signals 19, 20, and 21 input from the logic gate 9 when the signal 19 specifying the light intensity is , as the output signal 47,
When the signal 44 with the maximum pulse width is selected and the signal 20 specifying the light intensity "medium" is "1", the signal 45 with the intermediate pulse width is selected as the output, or the signal specifying the light intensity "weak". When 21 is "1", the signal 46 with the minimum pulse width is selected as the output. In other words, the pulse width of the output signal 47 changes depending on the control signals 19 to 21, and the amount of light is controlled by the eight-power signal 47.

That is, since the laser 25 is on while the output signal 47 is "1", it is possible to obtain the amount of light corresponding to each pulse width.

[Effects of the Invention] As explained above, according to the present invention, it is possible to reproduce with high quality both isolated exposed dots in an image made up of unexposed dots and isolated unexposed dots in an image made up of exposed dots. becomes.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a diagram explaining the processing algorithm of the embodiment, Fig. 3 is a diagram showing the relationship between laser drive current and optical output, and Fig. 4 is a diagram illustrating the relationship between laser drive current and optical output. FIG. 5 is a schematic diagram of the potential on the drum; FIG. 6 is a block diagram showing another example of the laser drive circuit according to the present invention; FIG. 7 is a diagram showing the details of the laser drive circuit according to the present invention. FIG. 8 is an explanatory diagram of laser drive pulses; FIG. 9 is a schematic configuration diagram related to the image forming operation of the laser beam printer; FIGS. 10 and 11 The figure is a diagram showing the relationship between the potential on the photosensitive drum and the formed image. 1-6...Line memory, 7--Demultiplexer, 8...Data selector, 9...Logic gate, lO-14...Shift register, 15...Line counter, 16... Laser drive circuit, 25...laser. Figure 3 V - Figure 4 ゝ ゝ > Ward〉)〉 Figure 6 Figure 8 Figure 9 Figure 10

Claims (1)

[Scope of Claims] 1) A recording device that records an image on a recording medium by scanning a light beam consisting of unexposed dots and exposed dots corresponding to image information on the recording medium, comprising: A storage means for storing three scanning lines in the scanning direction; and an exposed dot that is isolated among the non-exposed dots or a non-exposed dot that is isolated among the exposed dots based on the image information stored in the storage means. A recording apparatus comprising: a detection means for detecting dots; and a control means for controlling the amount of light of the light beam based on the detection result of the detection means. 2) In claim 1, the control means controls the amount of light when recording the recording pixel when the recording pixel is an exposed dot that exists isolated among non-exposed dots as a result of detection by the detection means. A recording apparatus characterized in that, when the recorded pixel is an exposed dot adjacent to a non-exposed dot that is isolated among exposed dots, the amount of light when recording the recorded pixel is weakened.