JP3606340B2 - Image recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image recording apparatus, and more specifically, scans an exposure beam modulated in accordance with image data in the main scanning direction of the photosensitive material, and sets the photosensitive material and the focused spot of the exposure beam as the main scanning direction. The present invention relates to an apparatus for exposing and recording a predetermined two-dimensional image on a light-sensitive material by relatively moving in an orthogonal sub-scanning direction.
[0002]
[Prior art]
As is well known, the flat-type output scanner turns on / off (modulates) the laser beam in accordance with the pixel pattern of the image data, scans the modulated laser beam in the main scanning direction of the photosensitive material, and sub-scans the photosensitive material. A predetermined image is exposed and recorded on the photosensitive material by being conveyed in the direction.
[0003]
The power density of the laser beam spot formed on the photosensitive material by the planar output scanner as described above usually follows a Gaussian distribution, and the photosensitive material is blackened because the accumulated energy exceeds a certain value, That is, on the light-sensitive material, the portion has a certain concentration or more (see FIG. 7A). On the other hand, whether or not the photosensitive material is blackened is not clearly separated by the threshold value of density, and naturally there is a boundary region. This boundary region is generally called a fringe region, and adversely affects the image quality (for example, unevenness). Therefore, the fringe region is preferably as narrow as possible.
[0004]
[Problems to be solved by the invention]
By the way, the width in the sub-scanning direction of the blackened region generated on the photosensitive material by the laser beam spot substantially coincides with the width of the cut when the power distribution of the laser beam spot is cut at the threshold value for blackening. However, the main scanning direction is a little complicated. This is because the imaging position of the laser beam spot on the photosensitive material constantly moves in the main scanning direction even when the same dot is exposed, so the laser beam spot scanning speed and its drive waveform are This is because it is closely related to the blackening width in the main scanning direction. This will be described in more detail below.
[0005]
In general, the blackened region of the light-sensitive material is in the form of a distribution of stored energy given on the light-sensitive material. Therefore, if the spot is a stationary laser beam spot, the distribution is a Gaussian distribution. It becomes a distribution in the form of time integration with the drive waveform. At this time, since the imaging position of the laser beam spot does not change with time, the accumulated energy distribution becomes a Gaussian distribution similar to the accumulated energy distribution of the laser beam spot, and even if the drive pattern changes, The blackened area simply changes in the degree of blackening (accumulated energy amount).
[0006]
However, when the photosensitive material is actually exposed in the planar output scanner, the laser beam spot is scanned in the main scanning direction as described above, and the imaging position changes with time. In this case, the accumulated energy distribution generated on the photosensitive material has a shape obtained by convolving and integrating the Gaussian shape and the drive waveform of the laser beam power in terms of position and time.
[0007]
FIG. 9 shows an energy distribution formed on the photosensitive material when dots are recorded while the laser beam spot moves in the main scanning direction. In FIG. 9, the laser irradiation time is T1 to T20. Now, taking as an example the case where the drive waveform of the laser beam power is an ideal rectangle as shown in FIG. 9A, the accumulated energy distribution generated on the photosensitive material is irradiated at each time T1 to T20. The resultant energy distribution of the laser beam spot (see FIG. 9B) is synthesized (see FIG. 9C).
[0008]
As shown in FIG. 8A, the Gaussian distribution due to the moving laser beam spot (that is, the accumulated energy distribution of the laser beam spot in the main scanning direction) has a slower rise and fall than the Gaussian distribution due to the stationary laser beam spot. You can see that In other words, in the direction of exposure while scanning, the higher the scanning speed, the more the rise and fall of the blackened accumulated energy is smoothed. As a result, the width of the fringe area is increased, and the optical This is the same as degrading the imaging performance. Furthermore, in reality, it is impossible to make the drive waveform of the laser beam spot completely rectangular, and the drive waveform itself is generally rounded, so that the width of the fringe region is further increased. work.
[0009]
As is clear from FIG. 7A, the fringe region becomes narrower as the base of the accumulated energy distribution formed on the photosensitive material by the laser beam spot becomes narrower. Therefore, by increasing the drive pattern of the laser element from B1 to B2 in FIG. 7B, the gradient of the power density of the laser beam spot is made steep from A1 to A2 in FIG. It is conceivable to narrow the fringe region. However, in such a method, the blackening width becomes wider than originally expected, and the dots or halftone dots recorded on the photosensitive material become thick.
[0010]
Therefore, an object of the present invention is to provide an image recording apparatus capable of reducing the fringe width without increasing the blackening width.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, the exposure beam modulated according to the image data is scanned in the main scanning direction of the photosensitive material, and the photosensitive material and the focused spot of the exposure beam are relative to each other in the sub-scanning direction orthogonal to the main scanning direction. An apparatus for exposing and recording a predetermined two-dimensional image on a light-sensitive material by moving the image
A light emitting device for generating an exposure beam;
Drive signal generating means for generating a drive signal for driving the light emitting element on and off based on the image data;
Provided in connection with the drive signal generating means, the on-time width of the drive signal is shortened so that the blackening width of the accumulated energy distribution of the exposure beam on the photosensitive material becomes a predetermined width, and when the drive signal is on Drive signal deforming means for enlarging the front edge portion and the rear edge portion in comparison with the level of the central portion.
[0012]
[Action]
In the invention according to claim 1, the on-time width of the drive signal for driving the light emitting element on and off is adjusted so that the blackening width of the stored energy distribution of the exposure beam on the photosensitive material becomes a predetermined width. ing. Further, the front edge and the rear edge when the drive signal is on are made larger than the level at the center. As a result, the rising and falling of the stored energy distribution of the exposure beam on the light-sensitive material become steep and the bottom thereof becomes narrow. Therefore, the fringe width can be reduced without increasing the blackening width.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 6 shows an example of an energy distribution formed on the photosensitive material when a dot is recorded while the laser beam spot moves in the main scanning direction in the image recording apparatus of the present invention. Before describing a specific embodiment of the present invention, the principle of the present invention will be described with reference to FIG.
[0014]
As described above, in the conventional flat output scanner, the laser irradiation time is T1 to T20 (see FIG. 9). On the other hand, in the present invention, as shown in FIG. 6A, the driving waveform of the laser power beam starts from time T2 and ends at time T19. That is, the time during which the photosensitive material is irradiated with the laser beam is T2 to T19. As described above, in the present invention, the irradiation time of the laser beam is shortened compared to the conventional case. Moreover, in the present invention, the laser driving power at the leading edge and the trailing edge of the driving waveform of the laser power beam is made larger than the power at the intermediate portion.
[0015]
As described above, the distribution of the stored energy generated on the photosensitive material by applying the drive waveform of the laser power beam, which has been transformed into a shape different from the conventional one, to the laser light emitting element is the curve shown in FIG. It becomes like α. The accumulated energy distribution α shown in FIG. 6C is a combination of the energy distributions of the laser beam spots irradiated at times T2 to T19 (see FIG. 6B).
[0016]
As is apparent from FIG. 6C, the stored energy distribution α in the present invention has a steep rise and fall compared to the stored energy distribution β in the conventional planar output scanner. As a result, the fringe width F1 in the present invention is narrower than the fringe width F2 in the conventional flat output scanner. Further, since the accumulated energy distribution α in the present invention is narrower than the accumulated energy distribution β in the conventional flat-type output scanner, the blackening width is hardly changed from the conventional one. These optically bring about the equivalent effect of increasing the focusing characteristics of the laser beam spot.
[0017]
In the present invention, the amount by which the drive waveform of the laser power beam is shortened and the extent to which the power at both ends is made larger than the power at the center are not unambiguous and depend on various conditions of the apparatus and the light-sensitive material. It is determined.
[0018]
FIG. 1 is a diagram showing a configuration of a planar output scanner according to an embodiment of the present invention. In Figure 1, the laser beam 2 being modulated for image drawing leaving the laser oscillator 1, after being angular swing in rotator mirror 3, imaging on the photosensitive material exposure surface 5 through the F-theta lens 4 The image is formed into a beam spot 6 that moves and scans the photosensitive material exposure surface 5 at a constant speed. On the other hand, the conveying roller 7 conveys the roll sensitive material 8 downward in the figure by rotating with the other roller (not shown) sandwiching the roll sensitive material 8. A two-dimensional image is formed on the photosensitive material exposure surface 5 by both operations.
[0019]
The roller drive pulse motor 9 is rotated at a high speed by a pulse motor drive signal 11 sent from the processing unit 10. The rotation output of the roller drive pulse motor 9 is decelerated to an appropriate rotation speed by the speed reducer 15 and then transmitted to the conveyance roller 7 to rotate the conveyance roller 7. The rotator mirror drive motor 12 rotates the rotator mirror 3 according to the rotator mirror drive signal 13 sent from the processing unit 10. The start sensor 14 detects the timing before the beam spot 6 reaches the light-sensitive material exposure surface 5 and determines the exposure start position in the main scanning direction. The start sensor 14 is used to monitor and feed back the laser power every time the laser beam spot passes to stabilize the laser power. The processing unit 10 generates a rotating body mirror drive signal 13 and a pulse motor drive signal 11. Further, the processing unit 10 generates a signal that is a feature of the present embodiment, that is, a laser driving signal 18 for modulating and driving the laser oscillator 1.
[0020]
FIG. 2 is a block diagram showing a more detailed configuration of the processing unit 10 shown in FIG. In FIG. 2, the processing unit 10 includes a basic clock generation unit 20, a laser driving unit 21, a rotating body mirror driving unit 22, and a pulse motor driving unit 23.
[0021]
The basic clock generation unit 20 generates various clock signals for controlling the entire system of the processing unit 10. As a particularly interesting clock signal, a high-speed basic clock 24 for processing by the laser driving unit 21 is generated. Occur. The pulse motor drive unit 23 creates a pulse motor drive signal 11 for driving the roller drive pulse motor 9. The rotating mirror driving unit 22 generates a rotating mirror driving signal 13 for driving the rotating mirror driving motor 12 at a desired number of rotations. The laser drive unit 21 receives image data 17 input from the outside and generates a laser drive signal 18 having an appropriate laser power in synchronization with the image data 17. Note that the effect of reducing the fringe width without increasing the blackening width is achieved by converting the waveform of the laser drive signal 18 into a desired shape.
[0022]
FIG. 3 is a block diagram showing a more detailed configuration of the laser drive unit 21 shown in FIG. In FIG. 3, the laser drive unit 21 includes a laser deformation drive signal creation unit 30, a laser light amount setting unit 31, a laser light amount setting dial 32, and a laser drive signal creation unit 33.
[0023]
The laser deformation drive signal generation unit 30 takes in the image data 17 that is a digital signal, shortens the ON time of the image data 17 by the number of several clocks of the basic clock 24, and the ON timing and OFF timing (that is, the previous timing) A laser deformation drive signal 34 having a signal waveform having a higher power than the others is created only at the edge and rear edge). The laser light quantity setting unit 31 takes in the start signal 16 and monitors the current laser power emitted from the laser oscillator 1 in real time, so that the laser light quantity value signal 35 is set to the laser power set by the laser light quantity setting dial 32. Create The laser drive signal creation unit 33 generates the final laser drive signal 18 by multiplying the laser deformation drive signal 34 and the laser light quantity value signal 35.
[0024]
FIG. 4 is a block diagram showing a more detailed configuration of the laser deformation drive signal generation unit 30 shown in FIG. FIG. 5 is a timing chart for explaining the operation of the laser deformation drive signal generator 30 shown in FIG. Hereinafter, with reference to these FIG. 4 and FIG. 5, the structure and operation | movement of the laser deformation | transformation drive signal preparation part 30 which are the structure parts which are the characteristics of a present Example are demonstrated.
[0025]
The shift register 40 delays the image data 17 by several clocks of the basic clock 24, and then supplies it to the one input terminal of the AND gate 46 as an output g. The amount of delay in the shift register 40 is the amount by which the on-time width of the laser drive signal 18 is narrowed, that is, the amount of the accumulated energy distribution of the laser beam spot on the photosensitive material is narrowed.
[0026]
The AND gate 46 calculates the logical product of the output g from the shift register 40 and the original image data 17, and outputs a digital signal a in which the image data 17 is shortened by the delay. The output a of the AND gate 46 is level-converted by the operational amplifier 41. The output b of the operational amplifier 41 becomes a signal c whose rise and fall have become slightly gentle as the high-frequency component is removed by the low-pass filter 43. The output b of the operational amplifier 41 is given to the delay element 42 and delayed by the signal delay in the low-pass filter 43. The subtractor 44 subtracts the output signal c of the low pass filter 43 from the output signal d of the delay element 42. The adder 45 adds the output e of the subtractor 44 and the output d of the delay element 42 to output a drive signal f whose front edge and rear edge are larger in power than the center. This drive signal f becomes the laser deformation drive signal 34 as it is. The adder 45 also has a limiter function in which the lower limit value is set to a predetermined level (for example, 0). Thus, the adder 45 prevents the added output f from undershooting below a predetermined level.
[0027]
As described above, the laser deformation drive signal generation unit 30 is configured to have a laser deformation in which the on-time width of the original image data 17 is made shorter and the power at the front edge and the rear edge is larger than the power at the center. A drive signal 34 is generated. As a result, as described with reference to FIG. 6, the accumulated energy distribution of the scan beam spot 6 on the photosensitive material 8 has a sharp rise and fall compared to the accumulated energy distribution in the conventional planar output scanner. As a result, the fringe width is narrower than that of a conventional flat output scanner. In this embodiment, since the base of the accumulated energy distribution is narrowed, the blackening width is almost the same as in the past even if the rise and fall are steep.
[0028]
In the above-described embodiment, the circuit as shown in FIG. 4 is used to deform the waveform of the laser drive signal. However, an equivalent waveform is obtained by a circuit having another configuration (for example, a circuit that digitally processes everything). It is also possible to perform deformation.
[0029]
【The invention's effect】
According to the first aspect of the present invention, the on-time width of the drive signal for driving the light-emitting element on and off is adjusted so that the blackening width of the stored energy distribution of the exposure beam on the photosensitive material becomes a predetermined width. Since the front edge and the rear edge when the drive signal is on are made larger than the level at the center, the fringe width can be reduced without increasing the blackening width.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a planar output scanner according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a more detailed configuration of a processing unit 10 shown in FIG.
3 is a block diagram showing a more detailed configuration of a laser driving unit 21 shown in FIG.
4 is a block diagram showing a more detailed configuration of a laser deformation drive signal generation unit 30 shown in FIG. 3. FIG.
5 is a timing chart for explaining the operation of the laser deformation drive signal generation unit 30 shown in FIG. 4;
FIG. 6 is a diagram illustrating an example of energy distribution formed on a photosensitive material when a dot is recorded while a laser beam spot moves in the main scanning direction in the image recording apparatus of the present invention.
FIG. 7 is a diagram showing a stored energy distribution of a laser beam spot on a photosensitive material and a driving waveform thereof.
FIG. 8 is a diagram showing a relationship between a blackening energy distribution caused by a stationary laser beam spot and a blackening energy distribution caused by a moving laser beam spot.
FIG. 9 is a diagram showing an energy distribution formed on a photosensitive material when a dot is recorded while a laser beam spot moves in the main scanning direction in a conventional flat output scanner.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Laser oscillator 2 ... Laser beam 3 ... Rotating body mirror 4 ... F- ( theta) lens 7 ... Conveying roller 8 ... Roll sensitive material 9 ... Roller drive pulse motor 10 ... Processing part 12 ... Rotating body mirror drive motor 15 ... Reducer 21 ... Laser drive unit 30 ... Laser deformation drive signal creation unit

Claims (1)

The exposure beam modulated in accordance with the image data is scanned in the main scanning direction of the photosensitive material, and the photosensitive material and the condensing spot of the exposure beam are relatively moved in the sub-scanning direction orthogonal to the main scanning direction. An apparatus for exposing and recording a two-dimensional image on a photosensitive material,
A light emitting element for generating the exposure beam;
Drive signal generating means for generating a drive signal for driving the light emitting element on and off based on the image data;
Provided in association with the drive signal generating means, the drive signal is shortened so that the blackening width of the accumulated energy distribution of the exposure beam on the photosensitive material becomes a predetermined width, and the drive signal An image recording apparatus comprising: drive signal deforming means for enlarging a front edge portion and a rear edge portion at the time of turning on compared to a level at the center portion.

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