JPH1016290A - Basic clock signal generator, image correction unit and image recorder employing it, and image correction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct even a micro distortion of an image correctly. SOLUTION: Based on the output from an encoder 4 for detecting the rotation of a drum 1, a PLL(phase locked loop) circuit 601 generates a PLL clock. A dot clock counter 606 generates a dot clock every time when the PLL clocks corresponding to the number of preset data are counted. The preset data is set variably by a control circuit 607. A correction data corresponding to a plurality of writing positions is stored in a correction memory 605. A DDA 608 generates a carry signal every time when the dot clocks corresponding to the number of the correction data are generated. The control circuit 607 changes the preset data from '8' to '7' or '9' every time when the carry signal is provided. Consequently, the time interval for generating the dot clock is varied every time when the carry signal is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus for recording an image on a photosensitive material carried on the surface of a rotating drum, a basic clock signal generator applied to the image recording apparatus, and image correction. The present invention relates to an apparatus and an image correction method.

[0002]

2. Description of the Related Art A photosensitive material film is mounted on the surface of a cylindrical drum in one of the image recording apparatuses conventionally used for preparing a printing original plate, and this photosensitive material film is selectively exposed to light. In some cases, an image is recorded. That is, a writing light source such as a semiconductor laser is provided in the vicinity of the drum, and light modulated corresponding to an image to be recorded is emitted from the writing light source toward a photosensitive film on the drum. The main scanning is performed by rotating the drum at high speed around its axis, and the sub-scanning is performed by slowly changing the writing position by the writing light source at a constant speed along the axis of the drum. Thus, the surface of the light-sensitive material film is two-dimensionally scanned, and recording of a two-dimensional image is achieved.

[0003] The writing light source is driven in synchronization with a dot clock generated based on the output of an encoder attached to the rotating shaft of the drum. Thus, the dots are drawn at a timing synchronized with the rotation of the drum, so that a dot of a fixed size can be drawn at an accurate position without depending on the rotation of the drum. But actually,
Since the mounting position of the encoder with respect to the rotation axis of the drum may be displaced, even if a dot clock created based on the output of the encoder is used, it may not be possible to faithfully draw the image. May be formed. The causes of the image distortion include the displacement of the drum itself, the displacement of the drum mounting position with respect to the rotating shaft (assembly error), the positional displacement caused when the photosensitive film is mounted on the drum, in addition to the displacement of the mounting position of the encoder. There are various factors. The distortion of the drum itself refers to, for example, a case where the peripheral surface of the drum is not strictly a cylindrical surface but has a barrel shape or a drum shape (when the cylindricity is poor), or an outer peripheral surface of the drum. Strictly speaking, this is the case where the rotation axis of the drum is not parallel (the degree of parallelism is poor).

[0004] If the mounting accuracy of the encoder, the processing accuracy of the drum, and the assembly accuracy are increased, the distortion of the image is improved. However, an increase in accuracy leads to an increase in cost and an increase in assembling time, which leads to deterioration in productivity, which is not preferable. Therefore, it is conceivable to eliminate the above-mentioned distortion factor by devising a drawing process for the photosensitive material film.

For example, Japanese Patent Application Laid-Open No. 5-207250 discloses a technique for correcting image distortion caused by a displacement of an encoder mounting position. In the technology disclosed in this publication, a PLL (Phase Locked Loop) circuit that generates a dot clock based on an output signal of an encoder that has a variable generation frequency is applied. Specifically, a PLL circuit having a frequency divider whose frequency division ratio is variable is applied. Then, different frequency division ratios are set according to the rotational position of the drum detected based on the encoder output, whereby the frequency of the dot clock is variable for each rotational position of the drum. With this configuration, the dot drawing time is varied according to the rotational position of the drum, and as a result, an image without distortion can be recorded on the light-sensitive material film by eliminating the influence of the displacement of the mounting position of the encoder. I can do it.

[0006]

However, in the above-mentioned prior art, there is a problem that a dot clock of a target frequency cannot be obtained immediately when the frequency division ratio in the frequency divider is changed. That is, when the frequency division ratio is changed, P
The LL circuit is in an asynchronous state for a moment. Therefore, by the time the dock clock converges to the target frequency,
It requires a pull-in time until the L circuit locks in the synchronous state. Therefore, an appropriate dot clock cannot always be generated, and as a result, image distortion cannot be completely removed.

Further, when the dot clock frequency is changed by changing the frequency division ratio, it is difficult to correct a slight image distortion on the order of 10 μm, for example. In order to correct such minute image distortion, the frequency division ratio must be minutely changed, so that a frequency divider having a very large circuit configuration is required. In addition, if the frequency of the dot clock is to be changed by a very small value, the influence of the instability factor of the analog circuit element included in the PLL circuit cannot be avoided.

Therefore, the above-mentioned prior art is not very suitable for applications requiring extremely accurate drawing, such as, for example, creation of design drawings. Accordingly, an object of the present invention is to solve the above-mentioned technical problem and to provide a basic clock signal generator having a configuration capable of accurately correcting even minute image distortion.

Another object of the present invention is to provide an image correction apparatus capable of accurately correcting even a small image distortion. It is a further object of the present invention to provide an image recording apparatus capable of correcting even minute image distortion and recording an image without distortion. Still another object of the present invention is to provide an image correction method for accurately correcting even minute image distortion.

[0010]

According to a first aspect of the present invention, there is provided a basic clock signal for defining timing for drawing dots on a photosensitive material carried on a rotationally driven drum. A basic clock signal generating means for generating a basic clock signal based on an output of a rotation detecting means for detecting rotation information of a drum, the basic clock signal generating means corresponding to predetermined expansion / contraction correction data. Clock adjusting means for controlling the basic clock signal generating means for generating the basic clock signals at a time interval different from the reference time interval every time the number of basic clock signals is generated. It is a clock signal generator.

According to the present invention, when the number of basic clock signals corresponding to the predetermined expansion / contraction correction data is generated at the reference time interval, the next basic clock signal is generated at a time interval different from the reference time interval. . Therefore, when dots are drawn based on the basic clock signal, the drawing time of each dot of the number corresponding to the expansion / contraction correction data becomes the reference time, and the drawing time of the next formed dot becomes a time different from the reference time. . As a result, a dot having a size different from the standard size is mixed with the dot having the standard size at a rate corresponding to the expansion / contraction correction data. This makes it possible to expand and contract a line composed of a plurality of dots formed on the photosensitive material.

Thus, in the present invention, instead of changing the frequency of the basic clock signal, the basic clock signal generated at the reference time interval is replaced with the basic clock signal generated at a time interval different from the reference time interval. The expansion and contraction of the line are achieved by mixing. Therefore, the line can be expanded and contracted by a much smaller length than when the frequency itself of the basic clock signal is changed.

The basic clock generating means includes an original clock generating means for generating an original clock signal based on the output of the rotation detecting means and an original clock signal generated by the original clock generating means. It is preferable to include a counting means for generating a basic clock signal every time counting is performed for a number corresponding to the set data.
In this case, it is preferable that the clock adjusting means further sets the setting data in the counting means, and changes the setting data to change the generation time interval of the basic clock signal.

According to this configuration, the basic clock signal is generated by counting the original clock signal generated by the original clock signal generating means. In this case, it is not necessary to change the frequency of the original clock signal to change the time interval of generation of the basic clock signal. Moreover, the basic clock signal generating means is constituted by the counting means for generating the basic clock signal each time the original clock signal is counted by the number corresponding to the setting data. It does not affect the occurrence time interval. This makes it possible to accurately expand and contract the line by a very small length.

[0015] According to a third aspect of the present invention, the clock adjusting means outputs a command signal each time a basic clock signal is input and a number of basic clock signals corresponding to expansion / contraction correction data are input. Output means, and means for changing the setting data set in the counting means from the reference setting data to expansion / contraction setting data different from the reference setting data each time the command signal output means outputs a command signal. It may be something.

According to this configuration, a command signal is output each time the number of basic clock signals corresponding to the expansion / contraction correction data is generated, and the setting data of the counting means is changed from the reference setting data based on the command signal. Is done. As a result, it is possible to mix the basic clock signal generated at a time interval different from the reference time interval at a rate corresponding to the expansion / contraction correction data.

The invention according to claim 4 is an image correction apparatus applied to an image recording apparatus for recording an image on a photosensitive material carried on a rotating drum, and for preventing distortion of a recorded image. Expansion and contraction correction data storage means storing expansion and contraction correction data corresponding to a plurality of positions on the surface of the photosensitive material;
The expansion / contraction correction data reading means for detecting the drawing position on the photosensitive material and reading expansion / contraction correction data corresponding to the detected drawing position from the expansion / contraction correction data storage means, and the expansion / contraction correction data reading means. An image correction apparatus comprising: the basic clock signal generator according to any one of claims 1 to 3, which generates a basic clock signal adjusted based on expansion / contraction correction data.

In this configuration, expansion / contraction correction data storage means is provided, and the expansion / contraction correction data storage means stores expansion / contraction correction data corresponding to a plurality of positions on the surface of the photosensitive material. Then, expansion / contraction correction data corresponding to the drawing position on the photosensitive material is read. By operating the above-described basic clock signal generator based on the read expansion / contraction correction data, it is possible to appropriately expand / contract the line corresponding to each position on the photosensitive material.

According to a fifth aspect of the present invention, there is provided a drawing start position corresponding to a plurality of positions in a direction along a rotation axis of a drum and storing drawing start position data corresponding to a drawing start position of a line corresponding to the position. Data storage means, drawing start position data reading means for detecting a drawing position on the photosensitive material and reading drawing start position data corresponding to the detected drawing position from the drawing start position data storage means, and drawing start position data And a drawing start signal generating means for generating a drawing start signal defining a drawing start timing of one line at a timing set based on the drawing start position data read by the reading means. Item 5. The image correction device according to item 4.

According to this configuration, the data representing the drawing start position of the line corresponding to a plurality of positions on the photosensitive material is stored in the drawing start position data storage means. The drawing start position data is read in accordance with the drawing position on the photosensitive material, and a drawing start signal that defines the drawing start timing of one line is generated based on the drawing start position data. Thus, the adjustment of the line drawing start timing and the expansion and contraction of the line can be performed in combination, so that it is possible to flexibly cope with image distortion due to various factors.

According to a sixth aspect of the present invention, there is provided an image recording apparatus for recording an image on a photosensitive material carried on a rotationally driven drum, wherein the drawing position is moved in a direction along a rotation axis of the drum. A drawing means for recording dots on a light-sensitive material, an image correction device according to claim 4 or 5, and a basic clock signal generator provided in the image correction device according to claim 4 or 5. And a drawing control unit for driving and controlling the drawing unit based on a basic clock signal.

According to this configuration, since the drawing unit is driven and controlled based on the basic clock signal generated from the above-described basic clock signal generating device, an image recording apparatus capable of correcting even minute image distortion is realized. You. The invention according to claim 7 is applied to an image recording apparatus for recording an image on a photosensitive material carried on a rotationally driven drum, and is an image correction method for preventing distortion of a recorded image. Creating expansion / contraction correction data for preventing distortion of a recorded image corresponding to each of a plurality of positions on the material; and a number of basic clock signals determined based on the expansion / contraction correction data corresponding to the drawing position Is generated at the reference time interval, and if the number of basic clock signals determined based on the expansion / contraction correction data corresponding to the drawing position is generated at the reference time interval, the next time at a time interval different from the reference time interval Generating at least one basic clock signal, and thereafter generating a basic clock signal at a reference time interval; and drawing dots on a photosensitive material based on the basic clock signal. An image correction method characterized by comprising the step of controlling the driving means.

According to this method, it is possible to mix a basic clock signal having a time interval different from the reference time interval into the basic clock signal having the reference time interval based on expansion / contraction correction data corresponding to a plurality of positions on the photosensitive material. it can. Then, by controlling the driving of the drawing means based on the basic clock signal, it is possible to expand and contract the line in order to eliminate even minute image distortion.

The invention according to claim 8 is a step of generating drawing start position data corresponding to a drawing start position of a line corresponding to a plurality of positions in the direction along the rotation axis of the drum, Controlling the driving of said drawing means so as to start drawing one line at a timing determined based on drawing start position data corresponding to a drawing position on the photosensitive material. An image correction method according to item 7.

According to this method, it is possible to flexibly cope with image distortion due to various factors by controlling drawing start timing for each line and expanding and contracting the line.

[0026]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration of an image recording apparatus to which an embodiment of the present invention is applied. This image recording apparatus is of a cylindrical outer surface scanning type and is for recording an image on a photosensitive material film 2 mounted on an outer peripheral surface 1a of a cylindrical drum 1. The mounting of the photosensitive material film 2 on the drum 1 is performed by a film loader (not shown).

The drum 1 has a photosensitive material film 2 on the outer peripheral surface 1a.
Is rotated at high speed by the main scanning motor 3. An encoder 4 serving as rotation detection means for detecting rotation information of the drum 1 is attached near the end of the drum 1 opposite to the main scanning motor 3. The encoder 4 outputs an origin signal (C-phase pulse) indicating that the rotational position of the drum 1 is the origin position and an encoder pulse signal synchronized with the rotation of the drum 1. For example, 4096 encoder pulse signals are output corresponding to one rotation of the drum 1. The origin signal is in the main scanning direction Y
Used to determine the drawing position for

A drawing device 5 is provided near the drum 1 for selectively exposing the photosensitive material film 2 to record an image. The drawing device 5 is moved at a constant speed in the sub-scanning direction X along the rotation axis of the drum 1 while being guided by a rail (not shown) by a sub-scanning feed screw 8 rotationally driven by a sub-scanning motor 7. The drawing device 5
It includes a laser emitter 51 including a semiconductor laser element and an optical system related thereto, and an AOM (acousto-optic modulator) 52. The AOM 52 is controlled by the control unit 6 and is driven based on a drawing signal corresponding to an image to be recorded. As a result, the laser beam emitted from the laser emitter 51 reaches the surface of the photosensitive film 2 after being modulated by the AOM 51.

In this way, the photosensitive film 2 is raster-scanned by the main scanning by rotating the drum 1 and the sub-scanning by moving the drawing device 5 along the axis of the drum 1. At this time, the surface of the photosensitive material film 2 is exposed to a laser beam modulated in accordance with a drawing signal, whereby a two-dimensional image is recorded on the photosensitive material film 2.

The above-mentioned control unit 6 for generating a drawing signal
, The output signal of the encoder 4 is input. The control unit 6 outputs an appropriate drawing signal based on the output of the encoder 4 and realizes accurate drawing on the photosensitive material film 2. For this purpose, the control unit 6 includes a drawing correction device 60. The drawing correction device 60 outputs a dot clock that defines the drawing timing and a drawing start signal that gives the drawing start timing of each line based on the output signal of the encoder 4. The dot clock and the drawing start signal are input to an image processing circuit 61 as drawing control means. The image processing circuit 61 generates a drawing signal in synchronization with a dot clock based on image data input from a host (not shown) via an interface (I / F) circuit 62.

The control unit 6 further includes a main scanning clock generation circuit 63 for generating a clock signal for driving the main scanning motor 3 and a sub-scanning for generating a clock signal for driving the sub-scanning motor 7. A clock generation circuit 64 is provided. The main scanning clock generation circuit 63, the sub-scanning clock generation circuit 64, the drawing correction device 60, and the image processing device 61 are controlled by a microcomputer 65.

The microcomputer 65 includes a CPU 65
a, a ROM 65b and a RAM 65c.
Based on a program stored in advance in the OM 65b and / or a program loaded in the RAM 65c, each unit in the control unit 6 is controlled and necessary data is given to each unit. In connection with the sub-scanning feed screw 8 driven by the sub-scanning motor 7, a sub-scanning origin switch 9 for detecting that the drawing apparatus 5 is at the origin position is provided. The output is input to the microcomputer 65 of the control unit 6. When recording an image on the light-sensitive material film 2, the drawing device 5 is moved toward the origin position, and when the sub-scan origin switch 9 detects that the drawing device 5 has reached the origin position, the drawing device 5 The movement in the X direction is started, and the drawing process is started.

As will be described later in detail, the drawing correction device 60 has a function of changing the dot clock and a function of individually and variably setting the drawing start position for each line. With these two functions, the drawing correction device 60 has a function of correcting the influence of various image distortion factors such as a displacement of the mounting position of the encoder 4, a distortion of the drum 1, and a distortion caused by raster scanning. Therefore, before describing the configuration of the drawing correction device 60, an image distortion due to the above-described image distortion factor will be outlined.

FIG. 2 is a diagram for explaining image distortion caused by distortion of the drum 1. Outer peripheral surface 1a of drum 1
Is not a strict cylindrical surface and the cylindricity is not very good. In other words, for example, it is assumed that the outer peripheral surface 1a of the drum 1 has a drum shape, and the diameter near the axial middle is smaller than the diameter near the axial end. In this case, when a rectangular image is drawn, the photosensitive film 2
The image recorded on the drum 1 is, as shown in FIG.
The shape near the middle part in the axial direction becomes a drum-shaped shape that shrinks. This is because the main scanning speed on the surface of the light-sensitive material film 2 becomes relatively slow in the vicinity of the middle portion in the axial direction where the diameter is small, so that the length of the dot in the main scanning direction becomes short.

In order to eliminate such image distortion, first, as shown in FIG. 2A, each line is moved along the Y direction so that the drawing start position of each line is aligned with the upper end reference straight line LU. Translate in parallel. As a result, an image shown by a two-dot chain line in FIG. 2A is obtained. Further, as shown in FIG. 2B, the lines near the center may be extended, and the drawing end position of each line may be aligned with the lower end reference line LL which is a straight line parallel to the upper end reference line LU. As a result, a rectangular image indicated by a two-dot chain line in FIG. 2B is obtained. That is,
By controlling the drawing start timing for each line and individually setting the expansion / contraction magnification for each line, the distortion of the image due to the distortion of the drum 1 can be corrected.

Even when the outer peripheral surface of the drum 1 is not parallel to the rotation axis of the drum 1, that is, when the parallelism of the drum 1 is not good, image distortion can be prevented by the same correction. Further, when the photosensitive material film 2 is obliquely mounted on the drum 1 by the film loader,
Image distortion can be corrected by individually controlling the drawing start position for each line.

FIG. 3 is a diagram for explaining image distortion caused by a displacement of the mounting position of the encoder 4, and shows a state in which the center axis Ce of the encoder 4 is displaced from the rotation axis Cd of the drum 1. I have. In this case, the encoder 4
Are changed depending on the rotational position of the drum 1. That is, the number of pulses generated by the encoder 4 while the drum 1 rotates by a unit angle varies depending on the rotational position of the drum 1. Therefore, if the scanning line can be partially extended or shortened according to the rotational position of the drum 1, this problem can be solved.

The tilting of the encoder 4 also causes image distortion. However, the image distortion due to the surface tilt of the encoder 4 also depends on the rotational position of the drum 1 as in the image distortion due to the mounting position deviation. Therefore, by partially extending or shortening the line, it is possible to compensate for the influence of the tilt of the encoder 4. In this embodiment, as will be described later, one line is divided into 128 segments, and the expansion and contraction magnification of each segment is individually set, so that image distortion due to encoder mounting accuracy and the like can be reduced. Has been corrected.

The distortion of the image due to the expansion and contraction of the photosensitive film 2 in the Y direction can be corrected by the expansion and contraction of each line. FIG. 4 is a diagram for explaining rhombic deformation by spiral drawing. As described above, since the surface of the drum 1 is spirally scanned by the rotation of the drum 1 and the movement of the drawing device 5, the photosensitive material film 2 is raster-scanned by oblique scanning lines.
Therefore, each line is not strictly perpendicular to the axis of the drum 1 but has a certain minute angle. Therefore, when a rectangular image is drawn, strictly speaking, a parallelogram is recorded. For example, when the image recording apparatus is used as a plotter for creating a design drawing or the like, extremely strict drawing is required, and thus it is necessary to eliminate the rhombic deformation as described above.

In order to correct such rhombic deformation, the drawing start position may be made different at each position in the sub-scanning direction X according to the angle of the scanning line with respect to the rotation axis of the drum 1.
That is, by changing the drawing start timing for each line so that a side perpendicular to the side along the line is formed, an accurate rectangle can be formed as shown by a two-dot chain line in FIG.

FIG. 5 is a block diagram for explaining the configuration of the drawing correction device 60 configured to realize each of the above-described corrections. The drawing correction device 60 includes a PLL (Phase Locked Loop) circuit 601 as an original clock generating means for generating a PLL clock which is an original clock signal based on a dot clock by multiplying an output pulse of the encoder 4. It has. The multiplication ratio in the PLL circuit 601 is set to a value according to the required resolution. For example, the encoder 4 outputs 4 rotations of the drum 1 for one rotation.
096 pulse signals are output.
Is 1 meter, and if drawing is performed at a resolution of 4000 dpi, the multiplication ratio in the PLL circuit 601 is 307. In this case, 1257472 PLL clocks are generated for one rotation of the drum.

The PLL clock output from the PLL circuit 601 is input to the Y counter 602 and counted. The count value of the Y counter 602 corresponds to a drawing position (Y coordinate position) in the Y direction (main scanning direction). Y counter 60
Reference numeral 2 denotes, for example, a 21-bit up counter, which outputs a drum one rotation signal when a count value corresponding to one rotation of the drum 1 is reached. That is, the drum 1
Every time the motor makes one rotation, a drum one rotation signal is output.

The drum rotation signal is counted by the X counter 603. Therefore, the count value of the X counter 603 corresponds to a drawing position (X coordinate position) in the X direction (sub-scanning direction). X counter 603 is, for example,
It is a 14-bit up counter. X counter 603
The count value of the Y counter 602 is input to a correction memory 605 storing correction data for correcting image distortion, and is used as an address signal for reading out correction data corresponding to a drawing position. The correction data includes drawing start position data that determines the drawing start position of each line, and expansion / contraction correction data that determines the expansion / contraction magnification in the Y direction for each segment obtained by dividing each line. The correction memory 605 is a memory addressed by a 15-bit address signal, and is, for example, an EEPROM (electrically erasable / writable read-only memory). The upper 7 bits of the 15-bit address are specified by the upper 7 bits of the count value of the X counter 603. The address of the lower 7 bits of the correction memory 605 is specified by either the upper 7 bits of the count value of the Y counter 602 or the lower 7 bits of the count value of the X counter 603. Which one to use as the address of the lower 7 bits of the correction memory 605 is selected by the selector 604. The remaining one bit of the 15 bits of the address signal is the selector 604
Is a selection signal given to As described above, the Y counter 603, the X counter 603, the selector 604, and the like constitute an expansion / contraction correction data reading unit and a drawing start position data reading unit.

[0044] Y counter 602 and X counter 603
Is cleared by an origin signal (C-phase pulse) first supplied from the encoder 4 after the start of the recording operation. Therefore, the drawing coordinate position by the drawing apparatus 5 is represented by a set of the count values of the Y counter 602 and the X counter 603. The microcomputer 65 can access the correction memory 605. The microcomputer 65 has a function of writing necessary correction data to the correction memory 605.

On the other hand, the PLL output from the PLL circuit 601
The clock is input to the dot clock counter 606. The dot clock counter 606 has a function as a counting unit for generating a dot clock for drawing by dividing the frequency of the PLL clock. More specifically, the dot clock counter 606 converts the preset data set by the control circuit 607 into a PLL.
Counting down is performed based on the clock 601, and when the count value becomes “0”, one dot clock is generated. Therefore, by variably setting the preset data, the frequency of the PLL clock 601 can be divided by a plurality of types of division ratios.

The frequency division ratio in the dot clock counter 606 is set by the control circuit 607 to one of 1/7, 1/8 or 1/9. That is, the control circuit 607 supplies the dot clock counter 606 with
“7”, “8” or “9” is set as preset data. The normal frequency division ratio is 1/8 (preset data is "8").
One dot clock is output each time a pulse is output (every reference time interval), and one dot drawing is performed based on the dot clock. That is, Y of the dot to be drawn
The length along the direction corresponds to eight PLL clocks. If the dividing ratio is 1/7 (preset data is "7"), one dot is drawn while the PLL clock is output for 7 pulses, and the dividing ratio is 1/9 (preset data is "9"). ), One dot is drawn while 9 pulses of the PLL clock are output. That is, the dividing ratio is 1 /
If 7, the dot clock generation time interval is shorter than the reference time interval, and the length of the dot along the Y direction is reduced. If the frequency division ratio is 1/9, the dot clock generation time interval is longer than the reference time, and the length of the dot along the Y direction is extended.

The control circuit 607 determines the preset data to be given to the dot clock counter 606 by
The output data of the correction memory 605 and the DDA (Digital
feretial Analyzer: digital differential analyzer) 608. Preset data M is input from the microcomputer 65 to the DDA 608, and expansion / contraction correction data N is input from the correction memory 605. The preset data M corresponds to the number of drawing dots per rotation of the drum, and is one eighth of the number of PLL clocks per rotation of the drum. The expansion / contraction correction data N is obtained by converting the absolute length of a segment obtained by dividing one line into 128 equal parts into the absolute expansion / contraction length of one line.
It consists of a 20-bit value converted into the number of L clocks and 1 bit representing expansion or contraction.

The DDA 608 outputs N clocks while the M dot clocks are supplied from the dot clock counter 606.
The carry signals (corresponding to command signals) are output at substantially equal time intervals. In other words, a carry signal is output each time the number of basic clocks corresponding to the expansion / contraction correction data is input. Each time a carry signal is supplied from the DDA 608, the control circuit 607 changes preset data to be supplied to the dot clock counter 606 from “8” (corresponding to １ ／ frequency division), which is reference setting data, to “setting data for expansion / contraction”. 7 ”(corresponding to 1/7 frequency division) or“ 9 ”(1
/ 9).
After switching the preset data to “7” or “9”, when the number of clocks corresponding to the preset data, that is, 7 or 9 PLL clocks is supplied from the PLL circuit 601, the control circuit 607 operates as usual. The preset data “8” corresponding to the circumferential ratio 比 is set in the dot clock counter 606. As described above, the control circuit 607 and the DDA 608 correspond to a clock adjusting unit.

Whether the preset data is changed to “7” (shortened) or “9” (expanded) indicates expansion or shortening of the above-described expansion correction data N supplied from the correction memory 605. It is determined based on 1-bit data. Loading of the expansion / contraction correction data N to the DDA 608 is performed every time the address given to the correction memory 605 changes under the control of the control circuit 607. Specifically, the control circuit 607 supplies a load signal to the DDA 608 each time the least significant bit of the address signal output from the selector 604 changes.

The PLL clock is also input to the drawing start position counter 609. Drawing start position counter 60
In 9, drawing start position data is set from the correction memory 605 for each line. More specifically, the control circuit 607 supplies a load signal to the drawing start position counter 609 every time the Y counter 602 outputs one rotation signal. As a result, the drawing start position counter 609 has
At the start of drawing of each line, drawing start position data corresponding to the line is set from the correction memory 605.

The drawing start position counter 609 is, for example, a 21-bit down counter.
The drawing start position data set from 5 is down-counted, and when the count value falls below “0”, a carry signal is given to the control circuit 607. The control circuit 607 supplies a drawing start signal to the image processing circuit 61 (see FIG. 1) in response to the carry signal from the drawing start position counter 609 to start the drawing processing. Thus, drawing of each line is started at the timing specified by the drawing start position data.

FIG. 6 is a block diagram for explaining the configuration of the image processing circuit 61. The image processing circuit 61 includes a drawing width counter 612 in which drawing width data in the Y direction is set by the microcomputer 65. The drawing width counter 612 counts down the set drawing width data in synchronization with the dot clock, and outputs a carry signal when the count value falls below “0”. This carry signal is given to the reset input terminal R of the flip-flop (FF) 611 set by the drawing start signal. That is, a signal that rises in response to the drawing start signal and falls in response to the input of the dot clock for the drawing width data is output to the output terminal Q of the flip-flop 611. That is,
The pulse width of this signal corresponds to the drawing length in the Y direction.

The output signal of the flip-flop 611 is A
The signal is supplied to one input terminal of the ND gate 613.
A dot clock is input to the other input terminal of the AND gate 613. Therefore, the AND gate 61
No. 3 allows the dot clock to pass only while the output of the flip-flop 611 is rising. The dot clock that has passed through the AND gate 613 is frequency-divided by 分 by the frequency divider 614, and the video RAM (VRAM) 61
7 is input as a read signal. Image data is written into the VRAM 617 via the interface circuit 62 (see FIG. 1), and outputs image data in parallel in units of 1 byte (8 bits) in response to a read signal from the frequency divider 614. . This one-byte data is written in the shift register 615 in parallel. Shift register 6
The data written in 15 is shifted one bit at a time based on the dot clock before being divided by the frequency divider 614, and is output serially one bit at a time. Based on the serial output data, the driving circuit 616
A drawing signal for driving the AOM 52 (see FIG. 1) is output.

As described above, when one dot clock is given, a drawing signal corresponding to 1-bit image data is output in order to draw one dot. This drawing signal is kept unchanged until the next dot clock is input to the shift register 615. FIG. 7 is a diagram for explaining a storage mode of correction data in the correction memory 605. The storage area of the correction memory 605 intuitively corresponds to a rectangle obtained by developing the circumferential surface of the drum 1 into a plane. This rectangle is divided into, for example, 128 equal parts in the X direction and the Y direction, respectively.
The small rectangle obtained by this is defined as a cell. The correction memory 605 stores storage cells C (0,0), C (0,1), C (C) for storing correction data for each cell.
(0,2),..., C (0,127); C (1,0), C (1,1), C
(1,2),..., C (1,128); C (2,0), C (2,1), C
(2,2),..., C (2,127);
(127,1), C (127,2),..., C (127,127) are provided.

FIG. 8 is a diagram for explaining the configuration of each storage cell C. One storage cell C is composed of 8 bytes. First 3 bytes (24 bits)
Are used for storing drawing start position data indicating the drawing start position of each line. The next three bytes (24 bits) are used for storing the above-mentioned expansion / contraction correction data N corresponding to the expansion / contraction magnification in the Y direction. Here, one bit is a bit indicating expansion or contraction or shortening. The remaining two bytes are free.

Whether the drawing start position data stored in the first three bytes or the expansion / contraction correction data N stored in the next three bytes is read is determined by a selection signal for switching the selector 604. You. That is, when a selection signal for selecting the count value of the X counter 603 is given, the drawing start position data stored in the first three bytes is output. Then, when a selection signal for selecting the count value of the Y counter 602 is given, the expansion / contraction correction data N stored in the next two bytes is read.

By specifying the upper address of the correction memory 605, a plurality of storage cells shown in FIG. 7 are included in one column corresponding to the upper address j (where 0 ≦ j ≦ 127). 128 memory cells C (0, j), C
(1, j), C (2, j),..., C (127, j) are selected.
Further, by specifying a lower address i (where 0 ≦ i ≦ 127), 128 storage cells C (0, j),.
.., C (i, j),..., C (127, j) are selected, and the selected storage cell C (i, j) is selected.
The correction data stored in (i, j) is output.

When one rotation signal is supplied, control circuit 607 supplies selector 604 with a selection signal such that the lower 7 bits of the count value of X counter 603 are supplied as the lower address of correction memory 605. And then,
A load signal is given to the drawing start position counter 609. As a result, the drawing start position data at the address corresponding to the count value of the X counter 603 is changed to the drawing start position counter 609.
Will be loaded.

The control circuit 607 causes the upper 7 bits of the Y counter 602 to be selected as the lower address of the correction memory 605 at a predetermined timing after the loading of the drawing start position data into the drawing start position counter 609 is completed. The selection signal is input to the selector 604. Thereby, the Y counter 602 and the X counter are stored in the correction memory 605.
The address of the storage cell corresponding to the cell to which the drawing position represented by the count value of the counter 603 belongs is given, and the expansion / contraction correction data N is read from the storage cell.

That is, when controlling the drawing start position, the correction memory 605 functions as drawing start position data storage means for storing drawing start position data corresponding to each of 16384 (= 128 × 128) lines. Then, when controlling the expansion / contraction magnification in each micro cell area on the drum, the correction memory 605 functions as expansion / contraction correction data storage means that stores expansion / contraction correction data in each cell.

FIG. 9 is a diagram for explaining the principle of correcting the drawing start position. Regarding the drawing start position data, the correction memory 605 can be regarded as a line memory that stores the drawing start position of each line. By setting the drawing start position data in the drawing start position counter 609 when drawing each line, drawing is started at a timing individually determined for each line. Thus, the time δT from the reference time Tref to the drawing start time Ts
Can be different for each line. For example, in the case where the outer peripheral surface of the drum 1 is not a perfect cylindrical surface and the intermediate portion is a drum shape with an inward recess, as shown in FIG. The time δT is shortened, and the time δ until the start of drawing near the edge δ
By increasing T, it is possible to correct variations in the drawing start position due to distortion of the drum 1.

FIG. 10 is a diagram for explaining expansion / contraction correction of an image in the Y direction. The data M actually set in the DDA 608 is, for example, 157184, and the expansion / contraction correction data N has a value of, for example, about 30. In the following, for the sake of simplicity, M = 1000 and N =
Assume 100. In this case, the DDA 608 outputs a carry signal at a rate of one dot for every 10 dots.

Taking the case of extending a line in the Y direction as an example, as shown in FIG.
9 dots of normal size NS drawn based on a dot clock obtained by dividing the L clock by 1/8 (clock generated at a reference time interval corresponding to 8 PLL clocks) Then, a large dot LS is drawn based on the dot clock obtained by dividing the frequency of the PLL clock by 1/9. That is, the length of the large dot LS along the Y direction corresponds to nine PLL clocks. The length of the normal dot NS along the Y direction corresponds to eight PLL clocks.

The same applies to reduction in the Y direction. For example, when nine dots NS of a normal size are drawn, a small dot SS is drawn next. This small dot SS makes the PLL clock 1/7
The dots are drawn based on the dot clock obtained by frequency division, and the length along the Y direction corresponds to seven PLL clocks.

If N = 1, one large dot LS or one small dot SS is drawn during one rotation of the drum 1, and the remaining dots are dots NS of a normal size.
Therefore, one line is extended or shortened by a length corresponding to one PLL clock. Thus, for example, if the circumference of the drum 1 is 1 meter and the number of PLL clocks corresponding to one rotation of the drum 1 is 1257472, the line can be expanded and contracted in units of about 0.8 μm.

Next, how to determine the correction data will be described. The influence of the encoder mounting error and the surface inclination of the encoder appear equally everywhere on the line along the axis of the drum 1. Therefore, the contribution of the encoder mounting error and the like to the expansion / contraction correction data is equal between a plurality of cells aligned in the X direction, which is the direction along the axis of the drum 1.

On the other hand, distortion caused by the processing accuracy of the drum 1 is generally expressed on a line along the circumferential direction of the drum 1.
Appears equally everywhere. Therefore, the contribution from the processing accuracy of the drum 1 to the expansion / contraction correction data appears equally in a plurality of cells along the Y direction. Further, the distortion of the image due to the expansion and contraction of the film appears equally everywhere on the line along the circumferential direction of the drum 1 and X
No dependence on directional position. Therefore, the contribution from the expansion and contraction of the film to the expansion and contraction correction data appears equally for all the lines without depending on the position in the Y direction.

Therefore, the expansion / contraction correction data of each cell is
According to the position in the X direction and the position in the Y direction, if the contribution from the encoder mounting error, the contribution from the distortion of the drum 1 and the contribution from the expansion and contraction of the film are determined by superimposition, these are determined. The effect of the image distortion factor can be compensated. To summarize the above, after all, the expansion / contraction correction data N is expressed by the following equation (1).

N (x, y) = Y + C (x) + E (y) (1) where N (x, y) represents expansion / contraction correction data corresponding to the drawing position (x, y). Y (y) represents the contribution for correcting film expansion and contraction, C (x) represents the contribution for cylindricity and parallelism correction (distortion of drum 1), and E (y) represents Represents the contribution for encoder correction. The expression (1) indicates that the correction of the film expansion and contraction does not depend on the drawing position, the cylindricity and the parallelism correction depend only on the X direction position, and the encoder correction depends only on the Y direction position.

Further, for the correction of the rhombus deformation described with reference to FIG. 4, the individual setting of the drawing start position described above in relation to the correction of the distortion of the drum 1 can be used. That is, as shown in FIG. 11, on the upstream side in the X direction, the reference time T
If the time δT from ref to the start of drawing is set long, and the time δT from the ref to the drawing start position is set shorter on the downstream side in the X direction, the rhombus deformation can be corrected.

Also, when the photosensitive film 2 is mounted on the drum 1 by the film loader when the photosensitive film 2 is mounted on the drum 1 at a certain angle, the correction of the rhombic deformation is also possible. Similarly to the above, the image distortion can be corrected by individually setting the drawing start position for each line. Therefore, the drawing start position data is obtained by superimposing the contribution for correcting the cylindricity and parallelism of the drum 1, the contribution for correcting the rhombus deformation, and the contribution for correcting the film mounting error. Is determined, the correction of the distortion of the drum 1, the correction of the rhombus deformation, and the correction of the film mounting position shift can be achieved at the same time.

FIG. 12 is a diagram for explaining a specific method of creating correction data to be stored in the correction memory 605. An example of a grid pattern to be experimentally drawn to obtain the correction data is shown in FIG. Have been. For example, 5
A grid pattern at 0 mm intervals is recorded experimentally. Then, the length and the degree of bending are measured for the horizontal line segments UL and DL at the upper and lower ends and the vertical line segment CL at the center.
That is, a T-shaped ruler is applied to the central vertical line segment CL, and a line segment U with respect to a straight line perpendicular to the central vertical line segment CL.
The shift amount of each lattice point on L and DL is obtained. Thereby, the cylindricity and parallelism of the drum 1 and the distortion amount of the image due to the rhombus deformation are obtained, so that correction data for correcting the distortion of the drum 1 and correcting the rhombus deformation is obtained.
Further, correction data for correcting expansion and contraction of the film is obtained from the length of the central vertical line segment CL.

Further, the distance between the horizontal lines adjacent to each other in the Y direction is measured one by one to determine the distance between the horizontal lines at each rotational position of the drum 1. Based on this, correction corresponding to the displacement of the encoder mounting position or the like is performed. Data can be obtained. The correction data thus obtained is stored in the correction memory 6
By writing in 05, various image distortion factors including cylindricity and parallelism correction, encoder correction, rhombus deformation correction, film expansion / contraction correction, and film mounting error correction can be achieved.

As described above, according to this embodiment, the drawing start position can be individually set for each line, and the expansion / contraction magnification of each line can be individually set for each region on the outer peripheral surface of the drum 1. Thereby, corrections corresponding to various image distortion factors can be achieved at the same time. Thereby, an image without distortion can be recorded. The expansion and contraction of the line is P
Dot clock counter 606 for counting LL clock
This is achieved by variably setting preset data. That is, instead of changing the frequency of the PLL clock, the number of PLL clocks counted when generating the dot clock is changed to change the dot clock generation time interval. Therefore, unlike the case where the generation frequency of the PLL circuit is changed, the generation time interval of the PLL clock can be changed instantaneously.

Furthermore, since the preset data of the dot clock counter 606 is changed every time a predetermined number of dot clocks are generated based on the expansion / contraction correction data, the expansion / contraction magnification can be finely set over a wide range.
Further, since the dot clock generation time interval is increased or decreased by one PLL clock, the length of one PLL clock on the outer peripheral surface of the drum 1 with respect to the length of one rotation of the drum 1 is determined. The ratio becomes the minimum expansion / contraction magnification, and such minute expansion / contraction can be accurately performed. More specifically, eight PLL clocks have a normal size of one.
Since it corresponds to a dot, the line can be expanded and contracted in units of 1/8 dot.

In the above description, it is assumed that every time the number of dot clocks corresponding to the expansion / contraction correction data is generated, the dot clock is generated at a time interval different from the reference time interval (for eight PLL clocks). As described above, such adjustment of the dot clock can also be viewed as follows. That is, it can be said that a dot clock having a frequency different from the reference frequency is mixed into the dot clock having the reference frequency at a rate corresponding to the expansion / contraction correction data. Further, the PLL clock is divided into a dot clock obtained by dividing the PLL clock at the reference division ratio (1/8) at a division ratio different from the reference division ratio at a ratio corresponding to the expansion / contraction correction data. It can also be said that the dot clock obtained by the circumference is mixed. Further, it can be considered that the dot clock is added or thinned out at a rate corresponding to the expansion / contraction correction data.

Although the present embodiment has been described above, the present invention is not limited to the above embodiment. For example, in the above embodiment, every time the number of dot clocks corresponding to the expansion / contraction correction data is generated, the time interval until the next one dot clock is generated is made different from the reference time interval. After the next one dot clock is generated, the dot clock is generated at the reference time interval. However, two or more dot clocks are continuously generated at a time interval different from the reference time interval. You may make it. In addition, it is possible to make various design changes within the technical scope described in the claims.

[0078]

According to the first aspect of the present invention, the frequency of the basic clock signal is not changed but the basic clock signal generated at the reference time interval is generated at a time interval different from the reference time interval. The expansion and contraction of the line is achieved by mixing the basic clock signal. Therefore, the line can be expanded and contracted by a much smaller length than when the frequency itself of the basic clock signal is changed. Moreover, the line can be expanded and contracted accurately without the problem of the response time caused when the frequency itself is changed.

According to the second or third aspect of the present invention, the basic clock signal generating means is constituted by a counting means for generating a basic clock signal every time the number of original clock signals corresponding to the set data is counted. Therefore, the unstable element of the circuit element does not affect the generation time interval of the basic clock signal. This makes it possible to accurately expand and contract the line by a very small length.

According to the fourth aspect of the present invention, the line can be appropriately expanded and contracted corresponding to each position on the light-sensitive material, so that the image can be corrected for various image distortion factors. According to the fifth aspect of the present invention, since the drawing start timing of each line can be individually controlled, adjustment of the drawing start timing of the line and expansion and contraction can be performed in combination.
As a result, it is possible to flexibly cope with image distortion due to various factors.

According to the sixth aspect of the present invention, there is provided an image recording apparatus capable of accurately correcting minute image distortion. According to the seventh aspect of the present invention, since the line can be minutely expanded and contracted according to the position on the photosensitive material, accurate correction corresponding to various image distortion factors can be performed. According to the eighth aspect of the present invention, it is possible to flexibly cope with image distortion due to various factors by combining the control of the drawing start timing for each line and the expansion and contraction of the line.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image recording apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a diagram for explaining correction of image distortion caused by distortion of a drum.

FIG. 3 is a diagram for explaining correction of image distortion caused by a displacement of an encoder mounting position.

FIG. 4 is a diagram for explaining correction of rhombus deformation.

FIG. 5 is a block diagram illustrating a configuration of a drawing correction apparatus.

FIG. 6 is a block diagram illustrating a configuration of an image processing circuit.

FIG. 7 is a diagram for explaining a storage mode of a correction memory.

FIG. 8 is a diagram illustrating a configuration of a storage cell.

FIG. 9 is a diagram illustrating correction of a drawing start position related to distortion of a drum.

FIG. 10 is a diagram for explaining expansion and contraction of a line.

FIG. 11 is a diagram for explaining control of a drawing start position for correcting rhombus deformation.

FIG. 12 is a diagram illustrating an example of a test image formed to create correction data.

[Explanation of symbols]

 Reference Signs List 1 drum 2 photosensitive material film 4 encoder 5 drawing device 6 control unit 60 drawing correction device 61 image processing circuit 65 microcomputer 601 PLL circuit 602 Y counter 603 X counter 605 correction memory 606 dot clock counter 607 control circuit 608 DDA 609 drawing start position counter

Claims (8)

[Claims] 1. A basic clock signal generator for generating a basic clock signal for defining timing for drawing dots on a photosensitive material carried on a rotationally driven drum, for detecting rotation information of the drum. A basic clock signal generating means for generating a basic clock signal based on the output of the rotation detecting means, and each time a number of basic clock signals corresponding to predetermined expansion / contraction correction data are generated, the basic clock signal is set to a reference time interval. A clock adjusting means for controlling the basic clock signal generating means to generate the clock signal at different time intervals. 2. The basic clock generating means according to claim 1, wherein said basic clock generating means generates an original clock signal based on an output of said rotation detecting means; Counting means for generating a basic clock signal each time counting is performed, the clock adjusting means setting the setting data in the counting means, and by changing the setting data, 2. The basic clock signal generator according to claim 1, wherein a generation time interval of the basic clock signal is changed. 3. The clock adjusting means includes: a command signal output means for outputting a command signal each time a basic clock signal is input and a number of basic clock signals corresponding to expansion / contraction correction data; And means for changing setting data to be set in the counting means from the reference setting data to expansion / contraction setting data different from the reference setting data each time the means outputs a command signal. 3. The basic clock signal generator according to 2. 4. An image correction apparatus applied to an image recording apparatus for recording an image on a photosensitive material carried on a rotationally driven drum, for preventing distortion of a recorded image, comprising: Expansion / contraction correction data storage means for storing expansion / contraction correction data corresponding to a plurality of positions; detecting a drawing position on the photosensitive material; and reading expansion / contraction correction data corresponding to the detected drawing position from the expansion / contraction correction data storage means. 4. A basic clock signal generating device according to claim 1, wherein said basic clock signal is generated based on expansion / contraction correction data read out by said expansion / contraction correction data reading unit. And an image correction device. 5. A drawing start position data storage means for storing drawing start position data corresponding to a drawing start position of a line corresponding to a plurality of positions in a direction along a rotation axis of a drum. Drawing start position data reading means for detecting a drawing position on the material and reading drawing start position data corresponding to the detected drawing position from the drawing start position data storage means; and reading the drawing start position data reading means. 5. The image correction apparatus according to claim 4, further comprising: a drawing start signal generating unit configured to generate a drawing start signal defining a drawing start timing of one line at a timing set based on the drawing start position data. apparatus. 6. An image recording apparatus for recording an image on a photosensitive material carried on a rotationally driven drum, wherein the drawing position is moved in a direction along a rotation axis of the drum.
Drawing means for recording dots on a photosensitive material; an image correction device according to claim 4 or 5; and a basic clock signal generator provided in the image correction device according to claim 4 or 5. An image recording device, comprising: a drawing control unit that drives and controls the drawing unit based on a basic clock signal. 7. An image correction method applied to an image recording apparatus for recording an image on a photosensitive material carried on a rotationally driven drum, for preventing distortion of a recorded image. Generating expansion / contraction correction data for preventing distortion of the recorded image corresponding to each of the plurality of positions; and adding a base clock signal of a number determined based on the expansion / contraction correction data corresponding to the drawing position to a reference time. If the number of basic clock signals determined at the reference time interval is determined based on the step generated at the interval and the expansion / contraction correction data corresponding to the drawing position, the next basic clock is generated at a time interval different from the reference time interval. Generating at least one signal and thereafter generating a basic clock signal at a reference time interval; and a drawing means for recording dots on the photosensitive material based on the basic clock signal. Controlling the drive. 8. A step of generating drawing start position data corresponding to a drawing start position of a line corresponding to a plurality of positions in a direction along a rotation axis of a drum, and a drawing position on a photosensitive material. 8. The image correction method according to claim 7, further comprising the step of: controlling the driving of said drawing means so as to start drawing of one line at a timing determined based on the drawing start position data corresponding to. Method.