JP2965858B2 - Internal expansion / contraction correction method of cylindrical inner surface scanning type image recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting internal expansion and contraction of a cylindrical inner surface scanning type image recording apparatus such as a digital direct printing plate exposure apparatus and an image setter.
The present invention relates to a method for correcting internal expansion and contraction of a duplicate image in the main scanning direction due to a relative axis shift between an optical axis of a light beam and an axis of a cylindrical drum.

[0002]

2. Description of the Related Art Conventionally, a deflector for deflecting a light beam modulated on the basis of a dot clock of a constant frequency is rotated at a constant speed around the optical axis of the light beam to perform main scanning and to perform constant scanning along the optical axis. 2. Description of the Related Art A cylindrical inner surface scanning type image recording apparatus that forms a duplicate image on a sheet-like photosensitive material mounted on the inner peripheral surface of a cylindrical drum by moving and sub-scanning is known.

FIG. 10 is a diagram showing a schematic configuration of a conventional cylindrical inner surface scanning type image recording apparatus. A sheet-shaped photosensitive material 200 is mounted on the inner peripheral surface 101 of the cylindrical drum 100. A polarizer 300 that deflects the light beam B modulated based on a constant dot clock is a motor (not shown).
Thus, the light beam is rotated around the optical axis O2 at a constant speed. The polarizer 300 is moved at a constant speed along the optical axis O2 of the light beam by a motor (not shown). Therefore, the light beam B scans the photosensitive material 200 in the main scanning direction X and the sub-scanning direction Y. As a result, a duplicate image is formed on the photosensitive material 200.

[0004]

By the way, in the cylindrical inner surface scanning type image recording apparatus as described above, the cylindrical drum 100
Ideally, the inner peripheral surface 101 is formed in a perfect circle with a constant radius over its entire length. Ideally, the axis O1 of the cylindrical drum 100 and the optical axis O2 of the light beam B completely coincide with each other. As described above, when the axis O1 of the cylindrical drum 100 is completely coincident with the optical axis O2 of the light beam B and the circularity of the cylindrical drum 100 is high, the optical axis O
The distance r between 2 and the inner peripheral surface 101 is constant. In this case, no internal expansion or contraction of the duplicate image formed on the photosensitive material 200 occurs.

However, in reality, the cylindrical drum 10
It is difficult to completely match the 0 axis O1 with the optical axis O2 of the light beam B. When the axis O1 of the cylindrical drum 100 is deviated from the optical axis O2 of the light beam B, as shown in FIG. 11, the distance between the optical axis O2 and the inner peripheral surface 101 is r1 to r3 depending on the main scanning position. So different. Also, in reality,
The inner peripheral surface 101 of the cylindrical drum 100 has unevenness relative to an ideal circular surface. Thus, even when the circularity of the cylindrical drum 100 is low, the cylindrical drum 1
A relative axis shift occurs between the axis O1 of the light beam 00 and the optical axis O2 of the light beam B, and the optical axis O2 and the inner peripheral surface 101 depend on the main scanning position.
Are different like r1 to r3. When such a relative axis shift occurs, conventionally, the frequency of the dot clock is fixed, so that the duplicate image on the photosensitive material 200 expands and contracts in the main scanning direction X as shown in FIG.

For this reason, conventionally, it has been necessary to increase the processing accuracy to the order of μm so that the inner peripheral surface 101 of the cylindrical drum 100 becomes a perfect circle with a constant radius. In addition, the axis O1 of the cylindrical drum 100 and the optical axis O2 of the light beam B are carefully aligned so that the distance between the optical axis O2 and the inner peripheral surface 101 is constant r at any scanning position. Had to do.
As a result, when the processing accuracy of the cylindrical drum 100 is increased, the cylindrical drum 100 becomes expensive, and furthermore, it takes a long time to perform the alignment operation, and thus has a problem that productivity is poor.

The present invention has been made to solve the above-mentioned technical problems, and to provide a method capable of correcting the internal expansion and contraction of a duplicate image even if the processing accuracy of a cylindrical drum is low or the alignment work is simplified. Aim.

[0008]

The invention according to claim 1 is
By rotating the deflector that deflects the light beam modulated based on the dot clock at a constant speed around the optical axis of the light beam and performing main scanning, and moving it at a constant speed along the optical axis and performing sub-scanning, the cylindrical drum is rotated. In a cylindrical inner surface scanning type image recording apparatus that forms a duplicate image on a sheet-shaped photosensitive material mounted on the inner peripheral surface of a cylindrical drum, the relative deviation between the optical axis of the light beam and the axis of the cylindrical drum is determined. A method of correcting internal expansion and contraction of a duplicate image in the main scanning direction due to the first step of forming an image for measuring internal expansion and contraction using a dot clock of a fixed frequency on a photosensitive material, comprising forming an image for measuring internal expansion and contraction A second step of previously obtaining a variable dot clock frequency required for each dot from the formation position of each dot in the main scanning direction and the sub-scanning direction, and when forming a desired duplicate image on the photosensitive material, A third step of generating a dot clock having a frequency determined in the second step according to a position where a dot is to be formed, whereby a relative position between the optical axis of the light beam and the axis of the cylindrical drum is provided. Regardless of the axis deviation, the pitch between the dots in the main scanning direction is made substantially constant, so that the internal expansion and contraction of the duplicate image formed on the photosensitive material in the main scanning direction is eliminated.

According to a second aspect of the present invention, in the first aspect, in the first step, an image for measuring internal expansion and contraction composed of a plurality of blocks divided in each of the sub-scanning direction and the main scanning direction is formed. In the second step, the frequency of the dot clock required only for the first main scanning line of each block of the internal expansion / contraction measurement image is obtained in advance, and the third
In the step, a dot clock of the frequency determined in the second step is generated for each dot of the first main scanning line of each block, and the dot clock of the frequency required in the second main scanning line of each block is generated. Interpolation of a dot clock having a frequency determined by the second step between the block and a block adjacent to the block in the sub-scanning direction, and calculating a dot clock having a frequency determined by the calculation. To be generated.

[0010] In the present specification, a cylindrical drum is used as a concept including not only a completely cylindrical shape but also a shape obtained by removing an arc portion having a predetermined central angle from a cylinder (for example, a half cylinder). I do.

[0011]

According to the first aspect of the present invention, in the first step, an image for measuring internal expansion and contraction is formed on the photosensitive material using a dot clock of a constant frequency, and in the second step, an image for measuring internal expansion and contraction is formed. When a variable dot clock frequency required for each dot is determined in advance from the formation position of each dot in the main scanning direction and the sub-scanning direction, and a desired duplicate image is formed on the photosensitive material in the third step, the formation of each dot is performed. A dot clock having the frequency determined in the second step is generated in accordance with the position to be set, so that the dot clock is generated between the dots regardless of the relative misalignment between the optical axis of the light beam and the axis of the cylindrical drum. Is made substantially constant in the main scanning direction so as to eliminate internal expansion and contraction in the main scanning direction of a duplicate image formed on the photosensitive material. As a result, the processing accuracy of the cylindrical drum may be low, and the alignment work can be simplified.

In the invention according to claim 2, the image for measuring internal expansion and contraction is formed in a first step, and the first main scan of each block of the image for measuring internal expansion and contraction is performed in a second step. The frequency of the dot clock required only for the line is obtained in advance, and in the third step, for each dot of the first main scanning line of each block, the second
The dot clock of the frequency obtained in the step is generated, and the frequency of the dot clock required for each dot of the main scanning line after each block is set to the block and the block adjacent to the block in the sub-scanning direction. Second
The interpolation calculation is performed from the dot clock of the frequency determined in the step (1), and the dot clock of the frequency determined by the calculation is generated. This simplifies the task of obtaining the required dot clock frequency in advance. Further, since the data amount is reduced, the memory capacity can be reduced, and the load on the interpolation calculation can be reduced.

[0013]

FIG. 1 is a perspective view showing the configuration of a cylindrical inner surface scanning type image recording apparatus according to an embodiment of the present invention. In FIG. 1, a cylindrical drum 1 is mounted on a base (not shown) so as to be vertically adjustable. The cylindrical drum 1 is formed with a hollow half-cylindrical inner peripheral surface 1A whose both ends and its upper part are open. The inner peripheral surface 1A of the cylindrical drum 1 is formed with a substantially constant radius r (for example, 225 mm) regardless of the position of the axis O1. On both sides of the cylindrical drum 1, a pair of support tables 1B and 1C are provided. A sub-scanning base 1D is laid on both supports 1B and 1C.
The support 1B is provided with an adjusting screw 1E for moving the sub-scanning base 1D left and right on the cylindrical drum 1.

A sub-scanning motor 2 is mounted on the sub-scanning base 1D.
And two rails 2A extending in the axial direction of the sub-scanning motor 2.
And a ball screw 2B having one end attached to the shaft of the sub-scanning motor 2, and a flange 2C rotatably supporting the other end of the ball screw 2B. Ball screw 2
In the middle of B, an arm 2D is attached movably along the rail 2A. At the lower end of the arm 2D,
The scanning head 3 is fixed. On one side of the cylindrical drum 1, an optical unit 4 for emitting a light beam B to the scanning head 3 is provided so as to be vertically and horizontally adjustable. A control circuit unit 5 is provided on the base.

FIG. 2 is a diagram showing a specific configuration near the scanning head 3, the optical unit 4, and the control circuit unit 5 in FIG. 2, a scanning head 3 includes a substantially U-shaped frame 31, an imaging lens 32 attached to one projecting side of the frame 31, and a main scanning motor attached to the other projecting side of the frame 31. 33, a deflector 34 rotatable around the rotation axis of the main scanning motor 33, and a start sensor 35. The deflector 34 has a deflecting surface 34A for deflecting the light beam B by 90 degrees. The start sensor 35 outputs a line start signal every time the light beam B is detected, in order to detect a reference point in one main scan of the light beam B. Optical unit 4
Includes a beam emitter 41 for emitting the light beam B, an AOM (acousto-optic modulator) 42 for modulating the light beam B based on an image signal, and a collimator lens 43 for converting the modulated light beam B into parallel light. Is provided.

The control circuit unit 5 includes a CPU 50, an electrically erasable and rewritable EEPROM 51, a main scanning motor reference clock generator 52, a sub-scanning motor reference clock generator 53, and a sub-scanning position counter 54. ,
Main scanning counter 55, hard register 56, D / A
A converter 57, a crystal oscillator 58, a waveform shaper 59,
And an image processing unit 60. The CPU 50 includes a ROM 50A, a RAM 50B, and a timer 50C for detecting a main scanning exposure start position. EE
A plurality of correction data for keeping the dot pitch ΔP in the main scanning direction constant is stored in the PROM 51 in advance (described later in detail).

Reference clock generator 52 for main scanning motor
Generates a reference clock having a constant frequency for rotating the main scanning motor 33 at a constant speed. Thereby, the deflector 3
4 rotates at a constant speed around the optical axis O2, that is, in the main scanning direction X. The sub-scanning motor reference clock generator 53 generates a reference clock having a constant frequency for rotating the sub-scanning motor 2 at a constant speed. As a result, the scanning head 3 moves the optical axis O
2, that is, at a constant speed in the sub-scanning direction Y.

When forming a normal image on the photosensitive material 6, the CPU 50 controls the main scanning counter 55 in the main scanning direction X according to a program stored in the ROM 50A in advance.
Set the number of dot clock pulses. The main scanning counter 55 counts the number of pulses of the dot clock, and outputs an area interrupt signal to the CPU 50 every time the counting of the set number of pulses is completed. The sub-scanning position counter 54 notifies the CPU 50 of the sub-scanning position of the light beam B on the cylindrical drum 1 by counting the number of pulses of the line start signal output from the start sensor 35. CPU 50
Reads the sub-scanning position from the sub-scanning position counter 54 to adjust the frequency of the dot clock when the area interrupt signal is generated, and stores the corresponding correction data in the EEPROM 5.
1 and the correction data is set in the hard register 56.

As shown in FIG. 3, the D / A converter 57
The data is converted into a DC voltage (for example, 0 to 5 V) corresponding to the correction data set in the hard register 56. As shown in FIG. 4, the crystal oscillator 58 has an oscillation frequency (for example, 10 to 15) in accordance with the DC voltage input from the crystal oscillator 58.
MHz). Therefore,
A dot clock having an arbitrary frequency can be obtained by the correction data set in the hard register 56. The dot clock output from the crystal oscillator 58 is subjected to waveform shaping by a waveform shaper 59, and is then supplied to an image processing unit 60 and a main scanning counter 55.

When assembling the cylindrical drum 1, the scanning head 3, and the optical unit 4, first, the vertical position of the cylindrical drum 1 is adjusted so that the axis O1 of the cylindrical drum 1 is horizontal. Next, by adjusting the adjusting screw 1E while making the optical axis O2 of the light beam B emitted from the optical unit 4 coincide with the rotation axis of the main scanning motor 33, the axis 1A of the cylindrical drum 1 and the optical axis O2 are substantially aligned. Align the axes so that they match.

Thus, the axis O1 of the cylindrical drum 1 is
When the mechanical alignment of the optical axis O2 of the optical unit 4 with the optical axis O2 of the optical unit 4 is completed, an electrical offset between the axis O1 of the cylindrical drum 1 and the optical axis O2 of the optical unit 4 is corrected. Alignment work is performed. By the way, when there is a relative axis shift as described above, internal expansion and contraction occurs in the main scanning direction X, and the dot pitch ΔP in the main scanning direction X shifts from a predetermined value (for example, 6 μm). Therefore, in order to obtain the frequency of the dot clock required for each dot, after mounting the photosensitive material 6 on the inner peripheral surface 1A of the cylindrical drum 1, the CPU 50
Read the reference image processing program from the ROM 50A,
It operates according to the reference image processing program.

First, the CPU 50 sets the frequency of the dot clock from the ROM 50A constant (for example, 12.5 MHz).
Is read and set in the hard register 56. As a result, a dot clock having a constant frequency is input to the image processing unit 60. On the other hand, the image processing unit 60 is provided with grid data as image data in order to draw an image for measuring internal expansion and contraction (for example, a grid image) as a test pattern on the photosensitive material 6. As a result, an image signal based on the constant frequency dot clock is provided from the image processing unit 60 to the AOM 42.

The light beam B emitted from the beam emitter 41 enters the AOM 42. An image signal for ON / OFF-modulating the light beam B from the image processing unit 60 is input to the AOM 42. ON / OF by AOM42
The F-modulated light beam B is applied to the deflecting surface 34A of the deflector 34.
Is incident on. Light beam B reflected from deflecting surface 34A
Is deflected in the direction of the inner peripheral surface 1A of the cylindrical drum 1. The deflected light beam B forms an image as a beam spot on the photosensitive material 6 mounted on the inner peripheral surface 1A. Here, the deflector 34
Are rotated at a constant speed in the main scanning direction X. Therefore, the light beam B is periodically deflected in the main scanning direction as the deflector 34 rotates at a constant speed. The scanning head 3 holding the deflector 34 is moved at a constant speed in the sub-scanning direction Y. Due to the constant speed rotation and the constant speed movement of the deflector 34, the light beam B
Indicates that two surfaces in the main scanning direction X and the sub-scanning direction Y
Record the dimensional image.

Therefore, when there is no relative axis deviation between the axis O1 of the cylindrical drum 1 and the optical axis O2 of the light beam B, the photosensitive material 6 has the main scanning direction X as shown in FIG. A lattice image without internal expansion and contraction is formed. On the other hand, when there is a relative axis shift, as shown in FIG.
A lattice image including internal expansion and contraction in the main scanning direction X is formed.
Note that this grid image is equally divided into n blocks in the main scanning direction X and m blocks in the sub-scanning direction Y. The black line portion of the grid image is formed with a fixed number of dots, and when there is a relative axis shift, the dot pitch ΔP in the main scanning direction X differs.

Incidentally, in order to eliminate internal expansion and contraction, the dot pitch ΔP in the main scanning direction of each dot of the image recorded on the photosensitive material 6 must be constant. To keep the dot pitch ΔP constant, the frequency of the dot clock must be changed according to the relative axis shift.

Here, r: drum radius, L: distance of one area of main scanning in the drum inner surface, F: number of rotations of light beam in main scanning (1/1)
Second), f: dot clock frequency (1 / second),
For example, when there are A dots in one main scanning area, equation (1) holds. L = (r · 2πF · A) / f (1) On the other hand, when the ideal one area distance is L0, if f = f0, the equation (2) is established. L0 = (r.2.pi.F.A) / f0 (2) Further, if the drum radius is r 'when the result of printing the lattice image on the photosensitive material 6 is L0', equation (3) is established. . L0 '= (r'.2πF.A) / f0 (3) Therefore, if L0' is measured, the dots required for each dot of the first main scanning line of each area can be obtained from the equations (1) to (3). The clock frequency is required. That is, this L0
Is actually measured by an optical length measuring device or the like, and a necessary dot clock frequency is obtained based on the measured data and the above equations (1) to (3).

By the way, as shown in FIG. 5, m blocks for measuring the internal expansion / contraction in the sub-scanning direction Y and n blocks B (0,0) to B (m-1, n-n) in the main scanning direction X are provided. 1), and the starting points P (0,0) to P (m−1, P) of the first main scanning line of each block B (0,0) to B (m−1, n−1)
The dot clock frequency required for only n-1) is determined in advance for the following reason. First,
In the cylindrical inner surface scanning type image recording apparatus, an image is recorded at a high density of, for example, about 2000 dpi in the main scanning direction X and the sub-scanning direction Y of the photosensitive material 6, for example. For this reason, finding the frequency of the dot clock for all the dots requires enormous effort. Therefore, if the measurement is performed only on the first main scanning line of each of the blocks B (0,0) to B (m-1, n-1), the operation of obtaining the frequency in advance can be simplified. Also, EEPROM
Since the data amount of the data 51 is reduced, the memory capacity can be reduced. The load on the CPU 50 for the linear interpolation calculation does not become large.

Therefore, the distance between the start point P (0,0) and the end point P (0,1) is measured for the block B (0,0), and the start point P (0,1) is measured for the block B (0,1). , 1)
And the distance between the end point P (0,2) and the subsequent points are measured in the same manner, and the start point P (m-1, n-1) of the last block B (m-1, n-1) is measured. End point P (m-1, n)
Measure the distance between them. Then, from the relationships shown in FIGS. 3 and 4, correction data D (i, j) of each starting point for obtaining a dot clock of a desired frequency for keeping the dot pitch interval constant is obtained, and this correction data D (i, j) is obtained. In advance in EEPROM5
1 is stored. FIG. 7 shows the storage format of the correction data.

For the main scanning lines after the second line in each block, a linear interpolation operation is performed from the correction data at the start point of the block and the correction data at the start point of a block adjacent to the block in the sub-scanning direction Y. , Correction data of a desired position is obtained. A dot clock having a desired frequency can be generated by using the correction data of the calculation result.

Next, in order to check whether the internal expansion and contraction in the main scanning direction X has been corrected, the exposure of the lattice image is performed on the photosensitive material 6 by using the correction data of the EEPROM 51 as in the case of drawing a normal image. Done. The operation in this case will be described with reference to the flowchart of FIG. First,
The CPU 50 sets the number n of main scanning divisions, and sets the number K of dots of one block (the total number of dots x / n in the main scanning direction) in the main scanning counter 55 (step S1). Next, when the main scanning motor 33 and the sub-scanning motor 2 rotate at a constant speed, the start sensor 35 generates a line start signal by receiving the light beam B (step S2). The sub-scanning position counter 54 detects the sub-scanning position by counting the number of clocks of the line start signal (step S3).

Next, the main scanning counter 55 counts the number of pulses of the dot clock from the time of receiving the line start signal, and detects the main scanning division position, that is, the starting point of the block (step S4). Note that the main scanning division position may be detected by the CPU 50 activating the timer 50C and measuring a fixed time from the time of receiving the line start signal. Next, the CPU 50 determines the main scanning division position n0.
Is set to "0" (step S5). Then, CPU
It is determined whether 50 is the main scanning line inside the block area, that is, the second main scanning line or later, or the first main scanning line (step S6).

In the case of recording the main scanning line inside the area, that is, the second and subsequent main scanning lines, for example, the main scanning line including the point C shown in FIG. 9, the correction data D1 of the starting point A of the block indicated by oblique lines and this The correction data D2 at the start point B of the block adjacent to the block in the sub-scanning direction is stored in the EEPROM.
The data is read out from the memory 51 (steps S7 and S8), and correction data at the sub-scanning position C is obtained by a linear interpolation operation (step S9). Here, as shown in FIG. 9, the correction data at the point C whose distance from the sub-scanning origin is L in the hatched block having the starting points A and B at the main scanning origin is obtained by the equation (4). Correction data of point C = D1 + {(D2−D1) · (L−N)} / M (4) where L: distance from sub-scan origin to sub-scan position C,
N: distance from sub-scan origin to area intersection A, M: length in block sub-scan direction, D1: correction data at point A, D
2: Correction data at point B. On the other hand, step S
In step S6, if it is not inside the block, that is, if it is the first main scanning line, it is only necessary to read the correction data of the starting point from the EEPROM 51 (step S1).
0).

When step S9 or S10 is completed,
The correction data is set in the hard register 56 (step S11). As a result, the crystal oscillator 58 generates a dot clock having a predetermined frequency based on the correction data. As a result, a dot clock having a desired frequency is generated from the waveform shaper 59 (step S12). As a result, the dot pitch ΔP for one main scanning line of this block is obtained.
Becomes constant. Next, the main scanning counter 55 counts down the number of dots K for each dot clock (step S13), and determines whether the counting of the number of dots K is completed (K ≦ 0) (step S14). If the counting has not been completed, the process returns to step S13 until the counting is completed.

When the counting is completed, that is, when the block reaches the end point of one main scanning line, the main scanning counter 55
Generates an area interrupt signal (step S15). CP
In response to the area interruption signal, U50 increments the main scanning division position by "1" (step S16), and determines whether the last block in the main scanning direction has been reached (step S17). If the last block in the main scanning direction has not been reached, the process returns to step S6. If the last block has been reached, it is determined whether or not all the sub-scans have been completed (step S18). If not, the process returns to step S2, and from the first block in the next sub-scan direction until all the sub-scans have been completed. Start image recording. As a result, even if there is a mechanical axis shift, all the lattice images are formed on the photosensitive material 6 without internal expansion and contraction in the main scanning direction as shown in FIG.

After confirming that the internal expansion / contraction has been corrected, the flowchart of FIG. 8 is executed for normal image data. As a result, this duplicate image can be recorded on the photosensitive material 6 without internal expansion and contraction.

In the above embodiment, the data is divided into a plurality of blocks. However, correction data may be obtained for each dot, and all the correction data may be stored in the EEPROM 51.

[0037]

According to the first aspect of the present invention, when a desired duplicate image is formed on a light-sensitive material, a dot clock having a frequency determined in advance according to a position where each dot is to be formed is generated. Thus, regardless of the relative axis deviation between the optical axis of the light beam and the axis of the cylindrical drum, the pitch between the dots in the main scanning direction is constant, and the main scanning direction of the image formed on the photosensitive material is maintained. To eliminate internal expansion and contraction.
Therefore, the processing accuracy of the cylindrical drum may be low, the simplified alignment work can be performed in a short time, and the internal expansion and contraction of the duplicate image can be corrected while improving the productivity.

In the invention according to claim 2, the image for measuring the internal expansion and contraction divided equally into a plurality of blocks is formed,
The frequency of the dot clock required only for the first main scanning line of each block is obtained in advance, and for each dot of the first main scanning line of each block, a dot clock of the frequency obtained in advance is generated. For each dot of the main scanning line after the block, an interpolation operation is performed from a dot clock of a predetermined frequency between the block and a block adjacent to the block in the sub-scanning direction, and the frequency of the frequency obtained by the operation is calculated. Since the dot clock is generated, the task of obtaining the required dot clock frequency in advance is simplified. Further, since the data amount is reduced, the memory capacity can be reduced, and the load on the interpolation calculation can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a cylindrical inner surface scanning type image recording apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration in the vicinity of a scanning head 3, an optical unit 4, and a control circuit unit 5 in FIG.

FIG. 3 is a diagram showing a relationship between input and output of a D / A converter 57 in FIG. 2;

FIG. 4 is a diagram showing an input / output relationship of a crystal oscillator 58 in FIG. 2;

5 is a diagram showing a state in which there is no relative axis deviation between the axis O1 of the cylindrical drum 1 and the optical axis O2 of the light beam B in FIG.

FIG. 6 is a diagram showing a state in which a relative axis shift between the axis O1 of the cylindrical drum 1 and the optical axis O2 of the light beam B in FIG. 1 occurs.

FIG. 7 is a diagram showing a storage format of correction data stored in an EEPROM 51.

8 is a flowchart showing the operation of the control circuit unit 5 in FIG.

FIG. 9 is a diagram for explaining linear interpolation.

FIG. 10 is a diagram showing a schematic configuration of a conventional cylindrical inner surface scanning type image recording apparatus.

11 is a diagram showing a state in which a relative axis shift occurs between the axis O1 of the cylindrical drum 100 and the optical axis O2 of the light beam B in FIG.

FIG. 12 is a diagram showing a state in which an image of a photosensitive material 200 has been internally expanded and contracted in a main scanning direction X.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cylindrical drum 1A ... Inner peripheral surface 2 ... Sub scanning motor 3 ... Scan head 4 ... Optical unit 5 ... Control circuit unit 33 ... Main scanning motor 34 ... Deflector 50 ... CPU 51 ... EEPROM 52 ... Reference clock for main scanning motor Generator 53 Reference clock generator for sub-scanning motor 54 Sub-scanning position counter 55 Main scanning counter 56 Hard register 57 D / A converter 58 Crystal oscillator 60 Image processing unit B Light beam O1 Axis O2: Optical axis

Claims (2)

(57) [Claims] A deflector for deflecting a light beam modulated based on a dot clock is rotated at a constant speed around the optical axis of the light beam to perform main scanning, and is moved at a constant speed along the optical axis to perform sub-scanning. Accordingly, in a cylindrical inner surface scanning type image recording apparatus that forms a duplicate image on a sheet-like photosensitive material mounted on the inner peripheral surface of a cylindrical drum, the relative position between the optical axis of the light beam and the axis of the cylindrical drum is reduced. A method for correcting internal expansion and contraction of a duplicate image in the main scanning direction caused by a temporary axis shift, wherein a first step of forming an internal expansion and contraction measurement image on the photosensitive material using a dot clock of a constant frequency, A second step of previously obtaining a variable dot clock frequency required for each dot from the formation position of each dot constituting the image for measuring internal expansion and contraction in the main scanning direction and the sub-scanning direction; When forming a duplicate image,
A third step of generating a dot clock having a frequency determined in the second step in accordance with a position where each dot is to be formed, whereby a relative position between the optical axis of the light beam and the axis of the cylindrical drum is provided. A method of correcting internal expansion and contraction in which the pitch between dots in the main scanning direction is made substantially constant irrespective of the axial displacement and the internal expansion and contraction of a duplicate image formed on the photosensitive material in the main scanning direction is eliminated. 2. In the first step, the image for measuring the internal expansion and contraction is formed of a plurality of blocks obtained by dividing each of the sub-scanning direction and the main scanning direction. In the second step, the internal expansion and contraction measurement is performed. The frequency of the dot clock required only for the first main scanning line of each block of the image for use is obtained in advance. In the third step, for each dot of the first main scanning line of each block,
A dot clock having the frequency obtained in the second step is generated, and the frequency of the dot clock required for each dot of the main scanning line after each block is set to be adjacent to the block in the sub-scanning direction of the block. 2. The internal expansion / contraction correction method according to claim 1, wherein an interpolation operation is performed from the dot clock of the frequency obtained in the second step with the block to be processed, and a dot clock of the frequency obtained by the operation is generated.