JPH07159715A - Device for correcting jitters of polygon mirror - Google Patents

Abstract

PURPOSE:To prevent the occurrence of unevenness of a stripe shape prolonging in the direction of sub-scan at the time of output. CONSTITUTION:A latch 17 and an encoder 18 select a dot recording clock signal synchronizing with a detection signal VS. A third counter 20 enabled by a flip- flop 22 counts the dot recording clock signal until the detection signal VE is outputted, and the latch 25 and the encoder 26 select the dot recording clock signal synchronizing with the detection signal VE also. A conversion table 28 calculates the transfer data imparting respective transfer timing, etc., from the subtraction value and the count values of both selection values, and further, the data are subtracted only by the random data. Thus, the data in a shift register 29 become the data whose respective transfer positions are changed at random. First, second counters 30, 31 control an adder 32 based on the transfer data, and a second selector 33 transfers and outputs a transfer dot recording clock signal phiX at a random time interval. The process is performed at every surface of scanning polygon mirror.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for correcting dot deviation (jitter) of a scanning line caused by a rotation error of a polygon mirror.

[0002]

2. Description of the Related Art In an image recording apparatus using a light beam scanning, represented by an output scanner and a laser printer, a polygon mirror (rotating polygon mirror) is generally widely applied as a light beam deflecting means for performing the scanning. It is being done. In this case, in order to prevent the scanning lengths of the respective scanning lines from varying, the angles of the respective surfaces of the polygon mirror in the main scanning corresponding direction are accurate, and all of them are finished to be perfectly flat (constant flatness). It is desirable that the polygon mirror rotates uniformly. However, in reality, it must be said that it is almost impossible to manufacture a polygon mirror that satisfies such demands. Therefore, it is caused by the above-mentioned angle error, flatness error, and rotation error of each surface. Due to the variation in the scanning lines, the positional deviation (jitter) of the dots occurs at the scanning end point of each scanning line. The occurrence of this jitter cannot be said to be preferable for the above-mentioned image recording apparatus that requires highly accurate image reproduction.

Therefore, as an effective means for correcting such a jitter, a method has been proposed in which the size of dots exposed at several intervals in one scanning line is increased or decreased to disperse the positional deviation of the dots. ing. Examples of such a technique include those disclosed in Japanese Patent Laid-Open No. 63-132214 and Japanese Utility Model Laid-Open No. 61-160418. More specifically, it is as follows.

First, regarding the above technique, time t /
N dot recording clock signals delayed from each other by N (t: time required to expose standard size dots, N: integer of 2 or more) are prepared in advance, and polygons are generated using these clock signals. For each surface of the mirror, the difference between the actual scanning time of the light beam and the standard scanning time is calculated with the time resolution t / N. Then, on the basis of the transfer timing and the transfer phase direction determined according to the value, the transfer dot recording signals are sequentially selected from the N dot recording clock signals, and the dot signals (dots) synchronized with this selected signal are selected. The on / off signal indicating the shading of the image is generated from the image signal, and then the light beam is modulated according to the dot signal. As a result, dot scanning clock signal transfer positions occur at equal intervals in each scanning line. Then, at each transfer position, the dot size fluctuates more or less than the standard size, and all the scanning end points coincide with each other in the sub-scanning direction.

On the other hand, in the above technique, the scanning time of the light beam is measured for each surface of the polygon mirror in the same manner as described above, but it is said that N dot recording signals are sequentially changed as described above. It achieves the same result as without adopting the configuration. That is, by controlling the frequency divider using the measurement value of the scanning time, the period of the reference dot recording clock signal is partially changed at equal intervals, and the positional deviation of each dot is dispersed over the entire scanning range. I have decided.

[0006]

The above-mentioned conventional technique is
Certainly, it is possible to prevent the occurrence of jitter in the main scanning direction, but in each case, when performing jitter correction in one main scanning direction, only one surface of the polygon mirror is focused on, and the other surface is It does not consider the influence and correlation in the sub-scanning direction due to. Therefore, when all or most of the scanning lines on each surface of the polygon mirror coincide with part of the above-mentioned transfer positions of the dot recording clock signal, unevenness (such as streaks in the sub-scanning direction) at the time of output ( A regular pattern) will occur. An example of such an example is shown in enlarged form in FIG.
It is 0. In particular, when outputting halftone dots for plate making,
As illustrated in, the unevenness causes unevenness on the edge of each halftone dot. Therefore, in order to prevent such unevenness, a jitter correction method that also includes sub-scanning information is essential.

The present invention has been made in order to newly solve such a matter of concern and is intended to prevent the occurrence of unevenness in the sub-scanning direction.

[0008]

[Means for Solving the Problems]

(1) According to the first aspect of the invention, a dot signal representing the density of each dot is created from an image signal in synchronization with a dot recording clock signal, and a light beam modulated according to the dot signal is sensed by a polygon mirror. In the image recording apparatus for recording the image indicated by the image signal on the sensitive material by scanning the material in the main scanning direction and moving the sensitive material in the sub-scanning direction orthogonal to the main scanning direction, the transfer dot recording clock signal A device used as a generator, the first sensor detecting passage of a light beam prior to scanning of each scanning line, and the second sensor detecting passage of a light beam after completion of scanning of each scanning line, A clock for generating a reference dot recording clock signal having a cycle t and a time t / N (N is an integer of 2 or more) for the signal based on the reference dot recording clock signal.
Dot recording clock signal generating means for generating N number of dot recording clock signals delayed one by one, random data generating means for outputting random data whose value randomly changes within a predetermined range, and each scanning line Every 1st
And the actual scanning required for the light beam to pass between the first and second sensors with a time resolution of time t / N using the detection signals and the N dot recording clock signals output by the second and second sensors, respectively. The time is detected, and through the subtraction processing of this actual scanning time and the preset standard scanning time, each transfer timing and transfer phase direction for performing transfer between N dot recording clock signals at equal intervals are obtained. A first crossover data calculation means for calculating the first crossover data to be given, and a second crossover data calculation means for calculating the second crossover data for each scanning line by adding or subtracting the first crossover data and the random data. , First for each scan line
One dot recording clock signal is selected from N dot recording clock signals according to the detection signal of the sensor, and another dot recording clock signal adjacent to the selected dot recording clock signal based on the second transfer data. And the transfer means for generating the transfer dot recording clock signal by sequentially transferring the N dot recording clock signals.

(2) In the invention according to claim 2, claim 1
The second transfer data calculating means in the above performs addition or subtraction processing with random data on all the transfer timing data included in the first transfer data.

(3) In the invention according to claim 3, the second transfer data calculating means according to claim 1 is only for the first transfer data corresponding to the first transfer from the selected dot recording clock signal. Addition or subtraction processing with random data is performed, and the first transfer data corresponding to subsequent transfer is output as the second transfer data without performing addition or subtraction processing.

[0011]

[Action]

(1) In the invention according to claim 1, the respective constituent parts interact with each other as follows. The clock generates a reference dot recording clock signal of cycle t to the dot recording clock signal creating means. In response to this, the dot recording clock signal creating means creates N dot recording clock signals,
These signals are output to the first transfer data calculating means and the transfer means. These dot recording clock signals are
It is a signal that is sequentially delayed by time t / N with respect to the reference dot recording clock signal.

On the other hand, both the first and second sensors detect the passage of the light beam and output the detection signal to the first transfer data calculating means. Further, the first sensor also outputs the detection signal to the transfer means. As a result, the first transfer data calculating means detects the actual scanning time with the time resolution t / N, and further performs a subtraction process of [(actual scanning time)-(standard scanning time)] to transfer at equal intervals. To calculate the first transfer data, and output this data to the second transfer data calculating means. The random data generating means also outputs the random data to the second transfer data calculating means. On the other hand, the second crossover data calculation means calculates the second crossover data by adding or subtracting random data to or from the first crossover data for the scanning line. As a result, the first transfer data is modified in whole or in part by the random data.

The transfer means selects one dot recording clock signal from N dot recording clock signals in response to the detection signal of the first sensor, that is, at the time of starting the scanning line, and selects the dot recording clock signal. The dot recording clock signal is output as the dot recording clock signal for transfer. After that, the transfer means changes from the transfer dot recording clock signal to another adjacent dot recording clock signal,
The transfer is sequentially performed based on the transfer timing and the transfer phase direction given by the second transfer data, and the dot recording clock signal that has been transferred for each transfer is output as a new transfer dot recording clock signal. Then, the light beam is modulated in synchronization with the respective transfer dot recording signals, and the scanning of the scanning line is performed.

When the first sensor detects the passage of the light beam again, the transfer operation using the random data is performed again on a new scanning line. Therefore, the second scan line data for the next scan line will be different from that for the previous scan line. as a result,
Each scan line changing position within one scanning line is different for each scanning line. This means that the transfer positions do not overlap with each other in the sub-scanning direction.

(2) Especially in the invention according to claim 2,
Since the transfer data calculating means adds or subtracts random data to or from all the first transfer data, all the first transfer data are randomly corrected. As a result, the transfer positions within the scanning line are randomly arranged in the main scanning direction, and the transfer positions are also randomly arranged in the sub scanning direction for each scanning line.

(3) In the invention according to claim 3, the second aspect
The transfer data calculating means performs addition or subtraction processing with random data only on the data corresponding to the first transfer among the first transfer data, and does not perform any addition on the first transfer data corresponding to the subsequent transfer. Do not add or subtract random data. Therefore, in the first transfer data, only the portion for the first transfer is randomly modified. Therefore, with respect to the main scanning direction, the first transfer position fluctuates randomly within a predetermined range, but after that, the transfer positions are arrayed at equal intervals. This means that the transfer positions are randomly distributed.

[0017]

【Example】

 <First embodiment>

FIG. 1B shows the principle of the transfer method (jitter correction method) according to the first embodiment of the present invention. From the viewpoint of clarifying the characteristics of this method by comparison, FIG. The conventional transfer method is also shown in (a). Further, for simplification, FIG. 2 shows a case where all the scan line transfer positions of the dot recording clock signal are the same for all the scanning lines. In FIG. 1, the symbol A indicates the main scanning base point, and the symbols B to H indicate the transfer positions. The first scan line, the next scan line,
For the nth scanning line, subscripts 0, 1, and n are added to the symbols A to H, respectively, to indicate the main scanning base point and each transfer position on each scanning line.

The principle of this embodiment is as follows. That is, the sequential transfer position from the dot recording clock signal selected at the start of main scanning to another adjacent dot recording clock signal is determined for each scanning line from the difference between the actual scanning time of the light beam and the standard scanning time. Although calculated (this point is the same as the conventional technique shown in FIG. 1A),
An actual transfer position is determined by adding or subtracting random data whose value fluctuates within a predetermined range RND (hereinafter referred to as a swing range RND) to or from each of these transfer positions. As a result, all the transfer positions are unevenly distributed not only in the main scanning direction but also in the sub scanning direction, and the transfer positions are never arranged in a line in the sub scanning direction. (Fig. 1
(See (b)).

FIG. 2 is a block diagram showing an outline of a plane scanning type image recording apparatus to which the jitter correction apparatus of the present invention is applied. This drawing is common not only to the first embodiment but also to a second embodiment described later.

The film feed roller 1 is rotationally driven by the sub-scanning motor 2, and in response thereto, the film 3 as the recording photosensitive material is fed in the sub-scanning direction indicated by the arrow. The image processing circuit 4 processes an image signal obtained from an input device or the like,
This is a section for outputting to the semiconductor laser 5 a dot signal V _DOT representing the density (including black and white) of each dot in synchronization with the transfer dot recording clock signal φ _X which is internally generated based on the above principle. Of these, the portion that generates the crossover dot recording clock signal φ _X is the crossover dot recording clock signal generation circuit 4B, and the portion that generates the dot signal V _DOT is the dot signal generation circuit 4A. Semiconductor laser 5
Outputs the light beam LB according to the received dot signal V _DOT . The light beam LB that is output with a divergence from the semiconductor laser 5 becomes a parallel beam by the collimator lens 6, is corrected by the cylindrical lens 7, and is irradiated on the reflection mirror surface of the polygon mirror 8.

In the present embodiment, the polygon mirror 8 is assumed to have a hexahedral reflecting mirror surface that reflects and deflects the light beam LB while rotating, and therefore, one scanning operation results in six scanning lines. To scan. Polygon mirror 8
The light beam LB reflected and deflected by the laser beam is mainly scanned on the film 3 via the fθ lens 9 and the cylindrical lens 10. The f.theta. lens 9 has condensing points of the same size irrespective of the position on the scanning line where the light beam LB arrives, and when the polygon mirror rotates by a certain angle, the condensed spot has a certain distance. It is for moving, that is, for enabling scanning on the scanning line at a constant speed. Similar to the cylindrical lens 7, the cylindrical lens 10 corrects the surface tilt of the light beam LB in the sub-scanning direction, and these are mainly for compensating the surface tilt error in the processing of the polygon mirror 8.

Immediately before the main scanning start position, in order to detect the passage of the light beam LB prior to the scanning of one scanning line, a start sensor 12 (first sensor) including a reflection mirror 11 and a photodetector such as a photodiode is used. Sensor) is provided. Immediately after the main scanning end position, a reflection mirror 13 and an end sensor 14 (second sensor) similar to the start sensor 12 are provided in order to detect passage of the light beam LB after scanning one scanning line. Has been. Detection signals from these sensors 12 and 14 are given to the image processing circuit 4.

Here, the dot shift amount ΔY at the end of the scanning line
Is represented by ΔY = L × J. In addition, L is a scanning length, and J is a rotation error (speed fluctuation rate). For example, assuming that L = 200 mm for main scanning on the short side of A4 size, and J = 0.02% as a rotation error of a commercially available and generally available polygon mirror, at the scanning line end at this time. The amount of dot deviation is ΔY = 200 x 0.0002 = 0.04 mm. Therefore, suppose the recording resolution is 1270 lines / in.
If it is ch (diameter of one dot d = 20 μm), the ratio of this dot shift amount to one dot is ΔY / d = 0.04 /
0.02 = 2. If there is a deviation of 2 dots, the straight edges of the recorded image will be considerably uneven, and it will not be possible to use it for a halftone plate consisting of a line drawing or a regular halftone dot pattern. I can't.

Therefore, in the embodiment of FIG. 2, the image processing circuit 4
, The number of dot recording clock signals φ ₁ will be described later.
~ Φ _N is generated, and one of these is used as the start sensor 12
Selection in synchronism with the detection signal of (that is, match the start position of each scan), starting from this selected dot recording clock signal, and changing the number of times according to the amount of dot deviation that should occur at random changing timing. The performed dot-change dot recording clock signal φ _x is created based on the above-described principle, and scanning is performed in synchronization with this signal φ _x .

FIG. 3 is a portion showing the configuration of the jitter correction apparatus as the first embodiment. In this apparatus, the sensor portion including the start sensor 12 and the end sensor 14 and the transfer dot in the image processing circuit 4 are arranged. The recording clock signal generating circuit 4B. The sensor portion is as described above. On the other hand, the transfer dot recording clock signal generation circuit 4B is provided with a clock unit (corresponding to the clock generator 15), a dot recording clock signal generating means unit (corresponding to the delay circuit 16), a first transfer data calculating unit unit, and a random transfer unit. It is roughly classified into a data generating means section, a second transfer data calculating means section, and a transfer means section. Among them, the first transfer data calculating means is a part for calculating the first transfer data which gives the transfer timing and the transfer phase direction at equal intervals, and includes the latch circuit 17, the encoder 18, the first selector 19, OR gate 21, D flip-flop 22, third
The counter 20, a latch circuit 24, a subtractor 23, a latch circuit 25, an encoder 26, a subtractor 27, and a conversion table 28 are included. On the other hand, the random data generator means is a part for generating random data (noise signal) whose value randomly changes within the above-mentioned swing range RND, and the random data generator 40 in the figure.
And a limiter 41. Further, the second transfer data calculating means is a part which corrects all the first transfer data with a random value and thereby creates the second transfer data, and includes the subtracter 42 and the shift register 29 in FIG. Consists of.

Further, the transfer means is based on each transfer timing given by the second transfer data (which randomly changes within the swing range RND around the timing given by the first transfer data) and the transfer phase direction. N dot recording clock signals φ _{1 to} φ _N are sequentially transferred, and the transfer dot recording clock signal φ _x is an output portion to the dot signal generating circuit 4A. The latch circuit 17, the encoder 18, the first and second The counters 30 and 31, the adder 32, and the second selector 33. Therefore, the latch circuit 17 and the encoder 18 are components common to the first transfer data calculation means unit and the transfer means unit. still,
In this embodiment, the subtractor 42 is used as the main element of the second transfer data calculating means section (as is the case with the second embodiment described later), but an adder may be used instead. It is possible. The operation of each part will be described in detail below.

A reference dot recording clock signal φ ₀ is generated by a clock generator 15 such as a crystal oscillator, and the reference dot recording clock signal φ is passed through a delay circuit 16.
N dot recording clock signals φ _{1 to} φ _N are generated by delaying the period t of ₀ equally by N and delaying by t / N (note that φ ₀
= Φ ₁ ). These dot recording clock signals φ _{1 to} φ _N are used not only to create the transfer dot recording clock signal φ _x , but also to detect the amount of dot deviation on each reflecting mirror surface due to the rotation error of the polygon mirror 8. It Therefore, the time resolution of dot shift amount detection is t / N, and the length resolution is d / N (d is the dot diameter).

First, the detection signal V _{S of the} start sensor 12
If so, this detection signal V _S is given to the clock input of the latch circuit 17, and the states of the dot recording clock signals φ _{1 to} φ _N at that time are latched by the latch circuit 17. The encoder 18 encodes the latched contents of the latch circuit 17, (the "1" rise immediately after the detection signal V _S i.e. the start sensor 12) in synchronization with the detection signal V _S of the start sensor 12 dot recording clock A signal indicating the sequence number of the signal is output. Encoding in the encoder 18 can be performed, for example, by identifying the head of consecutive "0" s or the "0" immediately after the consecutive "1" s. The output of the encoder 18 is given to the first selector 19, which selects the corresponding dot recording clock signal and outputs it to the third counter 20.

Further, the detection signal V of the start sensor 12
_S is a D flip-flop 22 via an OR gate 21.
Is also applied to the clock input of the D flip-flop 22, and the Q output of the D flip-flop 22 rises to "1". This Q output is given to the enable terminal of the third counter 20, and the third counter 20 is activated to count the selected dot recording clock signal in response to its rising edge. After that, if there is a detection signal from the end sensor 14,
This detection signal is applied to the clock input of the D flip-flop 22 via the OR gate 21, and the Q output of the D flip-flop 22 falls to "0". Therefore, the third counter 20 is disabled and the counting is finished. This count value indicates the number of dots that can be recorded between the start sensor position and the end sensor position, but the last 1 count does not correspond to a complete 1 dot (that is, 1 cycle of the dot recording clock signal). Since it is not valid, it is excluded as follows.

That is, the subtractor 23 receives the count value and subtracts the reference count value preset in the latch circuit 24 through the CPU or the like from the count value. For example, it is assumed that the position from the start sensor position to the end sensor position is associated with 200 mm on the short side of the A4 size, and the main scanning is performed with a resolution of 1270 lines / inch (dot diameter = 20 μm). In this case, the standard number of dots is 200 ÷ 0.02 = 10000 (dots), but since the last 1 count of the count values of the third counter 20 is not valid, it is excluded by subtraction. 10001 obtained by adding 1 to 10000 is set in the latch circuit 24 as a reference count value. Here, if the count value of the third counter 20 is, for example, 10002, the subtraction result of the subtractor 23 is 10002−10001 = + 1, which indicates that the dot shift amount in dot units is +1 dot. At that time, the symbol + indicates that the rotation speed of the reflecting mirror surface of the polygon mirror 8 deviates to the slower side than the standard, and the scanning length of one scanning line becomes shorter than the standard (the end of one scanning line is the 10001th count). Until just before).

On the other hand, in order to detect the dot shift amount of less than 1 dot by the time resolution of t / N (the length resolution of d / N at the standard rotation speed), the following processing is performed. That is, in response to the detection signal V _E of the end sensor 14, the state of the dot recording clock signals φ _{1 to} φ _N at this time is latched in the latch circuit 25, which is encoded by the encoder 26 to detect the end sensor 14. The sequence number of the dot recording clock signal synchronized with the signal V _E is derived. This operation is similar to the above-described case in which the latch circuit 17 and the encoder 18 derive the sequence number of the dot recording clock signal synchronized with the detection signal V _S of the start sensor 12. The subtractor 27 receives the outputs of the encoders 18 and 26,
The output of the encoder 18 is subtracted from the output of the encoder 26. For example, when N = 10 and the outputs of the encoders 18 and 26 are 3 and 9, 9-3 = +
6 is required. In this case, it can be seen that the dot shift amount of less than 1 dot is (d / 10) × 6. If the subtraction result of the subtractor 27 is negative, the conversion table 2 in the next stage
In step 8, N is added to the negative subtraction result and treated as a positive value.

The dot deviation amount obtained as described above,
That is, the subtraction results of the subtracters 23 and 27 are given to the conversion table 28, and converted into the first transfer data representing the transfer timing and the transfer phase direction of the dot recording clock signal necessary for correcting the dot shift amount. It This table data is preset through the CPU or the like. For example, an example of how to obtain the table data when N = 10 and the standard number of dots for one scanning line is 10,000 is as follows.

[When the subtraction result of the subtractor 23 is +1 and the subtraction result of the subtractor 27 is +6] 10 × 1 + 6 = 16
Therefore, the total dot shift amount at this time is (d / 10) × 1
Since it is 6, the change of the dot recording clock signal is 16
It only has to be done. In order to evenly change 16 times in the middle of one scan (that is, 10,000 dots), 10000 /
Transfers must be performed every 17 dots. At this time, the fractional part is truncated, but the error caused by this is not a problem. Further, the subtraction result of the subtractor 23 is positive, which indicates that the scanning length of one scanning line becomes shorter than the standard as described above. Therefore, the phase change direction is the phase delay direction.

[When the Subtraction Result of Subtractor 23 is -2 and the Subtraction Result of Subtractor 27 is -3] As described above, -3
Is treated as 7. From 10 × (−2) + 7 = −13, the total dot shift amount at this time is (d / 10) × 13. Therefore, for the reason described above, the transfer may be performed every 10000/14 dots. Further, the subtraction result of the subtractor 23 is negative, indicating that the scanning length of one scanning line is longer than the standard, and therefore the phase change direction is the phase advance direction.

If there is no error, the first counter 30 is loaded with a value that does not cause a carry. Then, since the output of the second counter 31 remains 0, the transfer does not occur.

Further, the first crossover data thus obtained is input to one input terminal (A) of the subtractor 42.
Since the random data is input to the other input terminal (B), the subtractor 42 performs the subtraction process (first transfer data)-(random data) on all the first transfer data in one scanning line. Execute against. Here, since the random data has its upper limit and lower limit limited by the limiter 41 with respect to the noise data output from the random data generator 40, the random data has a fixed range (see FIG. 1).
The data is the data whose value changes from moment to moment within the swing width RND in (b). Therefore, in the subtraction process, different random data are subtracted for each first crossover data. Then, the subtractor 42 outputs the subtraction result to the shift register 29 as the second transfer data (data which gives the final transfer timing and transfer phase direction).

Under the above-mentioned conditions, assuming that the swing range RND is 100, the first transfer timing is 588 by subtracting 100 from 588, and the second transfer timing is 488 by adding 588 to 488. 107
6 and the third transfer timing becomes 1664 by adding 588 to 1076.

The shift register 29 is the start sensor 12
For each detection signal V _s of the polygon mirror 8, that is, for every ⅙ rotation of the polygon mirror 8, the second transfer data for each surface is shifted, and after one rotation of the polygon mirror 8, the second transfer data is transferred for each surface. 1 Output to the counter 30. Generally, it is known that there is a fairly accurate reproducibility and a regularity with respect to a rotation error for each surface during rotation of a polygon mirror. Therefore, there is no problem even if correction is performed using the error data of one rotation before, and the control is realistic.

In order to facilitate understanding of the subsequent operation, the dot recording clock signal φ ₃ is designated as the transfer timing, and the second transfer data gives U (delay) as the transfer phase direction. Will be explained. When the detection signal V _S of the start sensor 12 for the same reflection mirror surface of the polygon mirror 8 obtained after one rotation is obtained, the second transfer data is the second transfer data at the transfer timing = 3 from the shift register 29. The data in the transfer phase direction U (delay) is preset from the shift register 29 to the second counter 31 while being preset to the 1 counter 30. on the other hand,
At this time, at the same time, the latch circuit 17 and the encoder 18
By the action of, the sequence number of the dot recording clock signal synchronized with the detection signal V _S of the start sensor 12 is detected. Here, the description will proceed assuming that the dot recording clock signal synchronized with the detection signal V _S of the start sensor 12 is φ ₃ and the sequence number = 3 is obtained from the encoder 18.

The second counter 31 detects from the detection signal of the end sensor 14 of the previous scan to the start sensor 12 of the current scan.
Is reset during the blanking period up to the detection signal, and thus the count output of the second counter 31 is 0 at the beginning. Similarly, the D flip-flop 22 and the third counter 20 are reset during the blanking period. On the other hand, the first counter 30 receives the detection signal V _S of the start sensor 12 and is loaded with the load value 3. Therefore, immediately after the detection signal V _S of the start sensor 12 is output, the encoders 18 to 3 and the second counter 31 to 0 are given to the adder 32, and the addition value 3 is given to the second selector 33. . The second selector 33 is
In response to this, the third dot recording clock signal φ ₃ is selected from the dot recording clock signals φ _{1 to} φ _N ,
This signal φ ₃ is output as the crossover dot recording clock signal φ _x . The transfer dot recording clock signal φ _x is given to the clock inputs of the first and second counters 30 and 31, but the enable terminal of the second counter 31 is connected to the carry output of the first counter 30 and there is the carry output. Until then, the second counter 31 is disabled, so that the first counter 30 alone counts.

The first counter 30 counts down one by one from the preset value 3 at each rising edge of the transfer dot recording clock signal φ _x . Count value is 1
Then, the carry output of the first counter 30 rises and the second counter 31 is activated. Then, in response to the next rising edge of the transfer dot recording clock signal φ _x , the second counter 31 counts up from 0 to 1, and the count value becomes 1. The up-count instruction is given by the preset data in the transfer phase direction U (delay) described above. If the transfer phase direction is D
If it is (advance), the down count is performed and the count value becomes -1. Further, since the carry output of the first counter 30 falls at the same time when the count value of the second counter 31 becomes 1, the second counter 31 is disabled again, and at the falling edge thereof, the first counter 30 is preset. The value 3 is loaded.

When the count value of the second counter 31 becomes 1, both inputs (A, B) of the adder 32 become 3 and 1, so that the addition output becomes 4. The second selector 33 is
In response to this, the dot recording clock signal φ ₄ is selected,
This time, change this signal φ ₄ to the dot recording clock signal φ
Output as _x . In this way, the transfer to the dot recording clock signals adjacent in the phase delay direction is performed. As described above, the transfer timings or the intervals between transfer positions are all random values.

The same operation is repeated at irregular time intervals. In this case, φ is changed at random intervals every 3 cycles (that is, 3 dots) of the transfer dot recording clock signal φ _x.
The transfer is sequentially performed in the order of ₃ → φ ₄ → φ ₅ → φ ₆ , and thereby the transfer dot recording clock signal φ _x is created. As described above, by performing scanning in synchronization with the transfer dot recording clock signal φ _x , it is possible to eliminate dots in the main scanning direction and to eliminate unevenness in the sub scanning direction.

In place of the delay circuit 16 of this embodiment, the clock generator 15 uses the dot recording clock signals φ _{1 to} φ.
Clock signal φ _{ORG with} a frequency N times _N (cycle t / N)
May be oscillated and divided and delayed to generate _N dot recording clock signals φ _{1 to} φ _N. This point is also common to the second embodiment described later.

Here, FIG. 4B shows a dot row on the film 3 obtained by using the present jitter correcting apparatus. Similar to the case of FIG. 1, FIG. 4 also shows a case where the scan line changing timings of the first scan line changing data are the same for all the scan lines at all the scan line changing positions. For comparison and comparison, FIG. 6A also shows an example of dots formed by a conventional device. As is clear from this comparison, in the present embodiment, all the dots (indicated by black circles in the figure) formed at the time of transfer are non-uniformly distributed not only in the main scanning direction but also in the sub scanning direction. Be understood.

<Second Embodiment>

FIG. 6 shows the principle of the transfer method in the second embodiment of the present invention, and FIG. 5 shows the conventional method. In both figures, the method of using the symbols indicating the main scanning base point and each transfer position is the same as in FIG. The principle of the second embodiment is as follows.

That is, the random data is added to or subtracted from only the first crossover data corresponding to the first crossover for each scanning line, and the correction is made.
It is intended to use the transfer data as it is.
As a result, the first transfer correction position B ₀ , B ₁ , ... B _n
As shown in FIG. 5B, are distributed randomly within a predetermined swing width RND. However, for the second and subsequent transfer, the transfer intervals in the main scanning direction are the same. That is, the distance B ₀ C ₀ = the distance C ₀ D ₀ = ...
= Distance G ₀ H ₀ , distance B ₁ C ₁ = distance C ₁ D ₁ = ... =
The distance is G ₁ H ₁ . As a result, when the dot arrangement is viewed as a whole, the dots are non-uniformly distributed in both the main scanning direction and the sub scanning direction.

FIG. 7 shows the configuration of a jitter correction apparatus that can realize the above principle. As described above, this apparatus is also applied to the image recording apparatus shown in FIG.
The difference from FIG. 3 (first embodiment) lies in the second transfer data calculation means unit.

The second transfer data calculating means section comprises a subtracter 42, a shift register 29 and a timing circuit 50. Of these, the subtractor 42 is the same as in the case of FIG. First, the conversion table 28, based on the results of the subtracters 23 and 27, converts the first transfer data into the U / D signal indicating the transfer phase direction and two types of load data indicating the transfer timing (first load data: The first transfer data and the second load data: subsequent transfer data are sent to the shift register 29. Immediately after the start,
In the timing circuit 50, the output Q ₂ becomes "L" level at the timing shown in FIG.
The load data is output to the first counter 30 via the subtractor 42 and the U / D signal is output to the second counter 31. As a result, the first load data is modified by the random data. This point is the same as in the first embodiment. At this time, the first counter 30 fetches the first load data at the timing of the transfer dot recording clock signal φ _x . When the transfer dot recording clock signal φ _x continues, the output Q ₂ of the timing circuit 50 becomes “H” level, and this time, the shift register 29 directly transfers the second load data to the first counter 30 without passing through the subtractor 42. Output. Of course, the U / D signal is also output. Therefore, the first transfer data is not modified by the random data. Then, the first counter 30 continues counting, and when the first counter 30 issues a carry, the second load data is loaded into the first counter 30. After that, since the output Q ₂ of the timing circuit 50 holds the “H” level, the second load data is loaded every time the carry occurs.

FIG. 4C shows a dot array obtained when this second embodiment is used. Regarding each scanning line, the first transfer position varies within the swing width RND, and thereafter, the transfer positions occur at equal intervals.

FIG. 9 shows the effects of the first and second embodiments. It can be immediately understood from this figure that the transfer positions are randomly scattered. Therefore, no regular pattern (unevenness) occurs in the sub-scanning direction.

<Others>

In the first and second embodiments, the film is used as the light-sensitive material, but printing plate material, printing paper, etc. may be used as the light-sensitive material. Further, the present jitter correction apparatus can be applied not only to the plane scanning type image recording apparatus but also to an image recording apparatus having a structure in which a sensitive material is attached on a cylinder rotatable in the sub-scanning direction.

[0056]

According to the first to third aspects of the present invention, the transfer positions of the dot recording clock signal can be dispersed for each scanning line, and the dot scanning clock signal extends in the sub-scanning direction, which has conventionally occurred during jitter correction in the main scanning direction. It is possible to prevent the occurrence of streaky unevenness.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the principle of jitter correction in the first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an image recording device using a polygon mirror, to which the jitter correction device of the present invention is applied.

FIG. 3 is a block diagram showing a configuration of a jitter correction apparatus according to the first exemplary embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an array of dots in a main scanning direction and a sub scanning direction obtained by the present invention.

FIG. 5 is an explanatory diagram showing an effect of the present invention.

FIG. 6 is an explanatory diagram showing an effect of a conventional technique.

FIG. 7 is an explanatory diagram showing the principle of jitter correction in the second embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of a jitter correction device according to a second embodiment of the present invention.

FIG. 9 is a timing chart showing the operation of the timing circuit in the second embodiment.

FIG. 10 is an explanatory diagram showing a conventional problem.

FIG. 11 is an explanatory diagram showing a conventional problem.

[Explanation of symbols]

3 film (photosensitive material) 4 image processing circuit 5 semiconductor laser 8 polygon mirror 12 start sensor 14 end sensor 15 clock generator 16 delay circuit 17, 24, 25 latch 18, 26 encoder 19 first selector 20 third counter 22 D flip-flop 23, 27, 42 Subtractor 28 Conversion table 29 Shift register 30 First counter 31 Second counter 33 Second selector 40 Random data generator 41 Limiter 50 Timing circuit V _S , V _E Detection signal φ ₀ Reference dot recording clock signal φ _{1 to} φ _N dot recording clock signal φ _x transfer dot recording clock signal LB light beam

Claims (3)

[Claims] 1. A dot signal representing the density of each dot is created from an image signal in synchronization with a dot recording clock signal, and a light beam modulated according to the dot signal is directed by a polygon mirror in the main scanning direction of a sensitive material. In the image recording device for recording the image indicated by the image signal on the sensitive material by moving the sensitive material in the sub-scanning direction orthogonal to the main scanning direction while generating the changeover dot recording clock signal. A device used as a device, comprising: a first sensor that detects passage of the light beam prior to scanning of each scanning line; and a second sensor that detects passage of the light beam after completion of scanning of each scanning line. , A clock for generating a reference dot recording clock signal of a cycle t, and a time t / N (N is 2 or more ), Dot recording clock signal generating means for generating N number of dot recording clock signals sequentially delayed, and random data generating means for outputting random data whose value randomly changes within a predetermined range; For each scanning line, the detection signals output from the first and second sensors and the N dot recording clock signals are used to perform a time resolution of the time t / N between the first and second sensors. The actual scanning time required for the light beam to pass through is detected, and through the subtraction processing of the actual scanning time and the preset standard scanning time, the N dot recording clock signals are transferred at equal intervals. First, each transfer timing and transfer phase direction for performing
First transfer data calculating means for calculating transfer data, and second transfer data calculating means for calculating second transfer data for each scanning line by addition or subtraction processing of the first transfer data and random data, For each scanning line, one dot recording clock signal is selected from the N dot recording clock signals according to the detection signal of the first sensor, and the selected dot is selected based on the second transfer data. Transfer means for generating the transfer dot recording clock signal by sequentially transferring the N dot recording clock signals from the recording clock signal to another adjacent dot recording clock signal,
A polygon mirror jitter correction device characterized by being provided. 2. The second transfer data calculation means performs addition or subtraction processing with respect to the random data on all the transfer timing data included in the first transfer data. Item 1. A polygon mirror jitter correction apparatus according to item 1. 3. The second transfer data calculation means performs addition or subtraction processing with the random data only on the first transfer data corresponding to the first transfer from the selected dot recording clock signal, The jitter correction of the polygon mirror according to claim 1, wherein the first transfer data corresponding to the subsequent transfer is output as the second transfer data without performing the addition or subtraction processing. apparatus.