JP3502709B2 - Stylus displacement control device and gravure engraving machine using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for controlling the displacement of a stylus provided on an engraving head of a gravure engraving machine. Furthermore, the present invention relates to a gravure engraving machine to which the above device is applied.

[0002]

2. Description of the Related Art A gravure engraving machine is an apparatus for forming a quadrangular pyramid-shaped minute hole called a cell on the surface of a cylindrical gravure cylinder which is copper-plated on its surface while rotating. The volume (depth and width) of the cells formed controls the amount of ink that fills the cells. Therefore, a desired image density can be obtained by controlling the depth and width of the cell.

An engraving head is used to form cells on the cylinder surface. The engraving head has a torsion shaft provided adjacent to the rotating gravure cylinder, a stylus holder fixed to the tip of the torsion shaft,
And a stylus (diamond tool) provided at the tip of the stylus holder. The torsion shaft is
The stylus at the tip of the stylus holder is displaced by being twisted by an actuator that uses electromagnetic force. Thus, by vibrating the stylus at a frequency of several kHz, regularly arranged cells are engraved on the cylinder surface.

FIG. 5 is a waveform diagram for explaining a signal waveform applied to the engraving head. FIG. 5A is a waveform diagram of a high frequency carry signal, and FIG. 5B is a waveform diagram of a density signal corresponding to the image density to be formed. By superimposing the carry signal and the density signal, the engraving signal of FIG. 5 (c) is obtained. A current signal corresponding to this engraving signal is applied to the engraving head, and an electromagnetic force for driving the actuator is generated. As a result, cells having a depth and a width corresponding to the concentration signal are engraved on the cylinder surface. In FIG. 5 (c), the chain double-dashed line R corresponds to the cylinder surface. Therefore, the shaded area below the chain double-dashed line R corresponds to a cell.

[0005]

The actuator driven by electromagnetic force has a large hysteresis with respect to the drive current. This will be described more specifically with reference to FIG. 17 showing the relationship between the displacement of the stylus and the static drive current. In the process of increasing the driving current, the displacement of the stylus follows the curve L1. On the other hand, in the process of decreasing the drive current, the displacement of the stylus follows the curve L2. That is, the stylus displacement follows different paths when the drive current increases and when the drive current decreases. Since the target displacement of the stylus is represented by a curve L0 that is intermediate between the curves L1 and L2, the difference between the curve L0 and the curve L1 or L2 is an error. As the cause of such hysteresis, influences of mechanical friction and residual magnetic flux can be considered, but their identification has not been reached.

FIG. 18 shows a Lissajous figure when a carry signal is superimposed. Along with the vibration of the drive current, the point representing the relationship between the displacement of the stylus and the drive current draws a boat-shaped elongated locus. As the density signal is increased, the Lissajous figure becomes r11, r12, r13, r14, r15,
It moves like r21. That is, the displacement of the stylus vibrates between the curve L11 and the curve L12. Moreover, when the density signal is decreased, the Lissajous figure becomes
r21, r22, r23, r24, r25, r26, r
It moves like 27, r28, r11. That is,
The displacement of the stylus oscillates between the curve L21 and the curve L22.

One of the ideal Lissajous figures is represented by reference numeral r0. That is, the ideal Lissajous figure is between the curve L01 between the curves L11 and L21 and the curve L02 between the curves L12 and L22.
The difference between the curve L01 and the curve L11 or L21, or the difference between the curve L02 and the curve L12 or L22 corresponds to the error in the size of the formed cell.

FIG. 19 is a diagram showing the displacement of the stylus tip with respect to the cylinder surface. The curve D1 represents the locus of the tip of the stylus in the process of transitioning from the state of forming shallow cells to the state of forming deep cells. A curve D2 represents the locus of the tip of the stylus in the process of transitioning from the state of forming deep cells to the state of forming shallow cells. The curve D0 represents the target displacement. As understood from FIG. 19, cells shallower than the target depth are formed in the period after the shallow cells are formed, and target depths are formed in the period after the deep cells are formed. A cell deeper than that is formed.

20 and 21 are diagrams for explaining the influence of hysteresis on an image actually formed. 20 and 21, the density of the image is represented by the density of the diagonal lines. For example, as shown in FIG. 20 (a), it is assumed that a high-concentration portion 92 should be formed in a tint portion (a region where the concentration does not change) 91. In this case, an engraving signal corresponding to the image density of each part in FIG. 20 (a) is applied to the engraving head, and the gravure cylinder is engraved. When printing is performed using the gravure cylinder thus obtained, the image of FIG. 20 (b) is obtained. That is, the high concentration portion 92A is formed in the tint portion 91A. However, on the downstream side of the high-density portion 92A in the engraving direction,
The pulling portion 92B having a higher concentration than the tint portion 91A is formed. This is because the stylus displacement is curve D2 in FIG.
If you have a history like, cell size (depth)
However, it is larger than the target size.

On the other hand, as shown in FIG. 21 (a), it is assumed that the low concentration portion 93 should be formed in the tint portion 91. In this case, the image shown in FIG. 21 (b) is obtained. That is, the low-concentration portion 93A is formed in the tint portion 91A, and the downstream side in the engraving direction is the tint portion 9A.
The pulling portion 93B having a lower concentration than 1A is formed. This is because when the displacement of the stylus has a history as shown by the curve D1 in FIG. 19, the cell size becomes smaller than the target size.

As described above, due to the influence of the above-mentioned hysteresis, there is a problem that remarkable density unevenness occurs particularly in the tint portion, and the image quality deteriorates. Therefore,
An object of the present invention is to solve the above technical problem and to provide a stylus displacement control device capable of reducing or eliminating the influence of hysteresis to form a cell having a target size.

Another object of the present invention is to provide a gravure engraving machine capable of obtaining an image having no density unevenness.

[0013]

The invention according to claim 1 for achieving the above object is a device for controlling the displacement of a stylus for engraving cells on the surface of a gravure cylinder, the displacement of the stylus. History calculating means for calculating the history of the stylus displacement, the correction amount calculating means for calculating the correction amount for canceling the hysteresis of the stylus displacement based on the history calculated by the history calculating means, and the target displacement; Based on the correction amount calculated by the means,
A stylus displacement control device, comprising: a correction unit that corrects an engraving signal for displacing the stylus.

According to this structure, the correction amount for canceling the hysteresis of the stylus displacement is calculated based on the history of the stylus. Then, the engraving signal is corrected based on this correction amount. As a result, the influence of the stylus displacement hysteresis is eliminated, so that it is possible to reliably form a cell of a desired size. As described in claim 2, the correction means corrects the image data corresponding to the target displacement based on the correction amount calculated by the correction amount calculation means, and creates the corrected image data. May be In this case, the engraving signal is created based on the corrected image data.

Further, as described in claim 3, the history calculation means calculates history data based on corrected image data corresponding to a plurality of cells before the image data changes. May be. As a calculation method, for example, a method of obtaining an average value of each image data after correction,
A method in which each image data is multiplied by a different weighting coefficient and then added is considered. As a result, it is possible to eliminate the influence of a sudden data change that has a small contribution to hysteresis.

Further, as described in claim 4, the correction amount computing means sets the state variable corresponding to the error of the stylus displacement with respect to the target displacement to the history data and the state variable before the change of the image data. It may include a means for calculating based on. As a result, a state variable is created based on the conventional stylus drive state, and therefore, by using this state variable, the influence of hysteresis can be satisfactorily eliminated.

Further, as described in claim 5, the correction means corrects the image data with a value obtained by multiplying the correction amount calculated by the correction amount calculation means by a fine adjustment coefficient, and the image data. The first fine adjustment coefficient is applied as the fine adjustment coefficient when increasing the value of, and the second fine adjustment coefficient smaller than the first fine adjustment coefficient is applied when decreasing the value of the image data. It is preferable to include means for applying as. This allows
Whether the image data is increased or decreased, the stylus displacement can be accurately controlled to a target value.

According to a sixth aspect of the present invention, there is provided a driving means which is driven by an engraving signal, and an engraving head provided with a stylus for engraving cells on the surface of the gravure cylinder when driven by the driving means, and the above-mentioned invention. A stylus displacement control device according to any one of 1 to 5, which is a gravure engraving machine.

According to this structure, the displacement of the stylus is
It is well controlled to eliminate the effects of hysteresis so that precisely sized cells can be engraved on the gravure cylinder surface. Therefore, the printed matter obtained by using the engraved gravure cylinder is of high quality with no density unevenness.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of the present invention will be described.
It will be described in detail with reference to the accompanying drawings. FIG. 1 is a front view showing a configuration of a gravure engraving machine to which an embodiment of the present invention is applied. 2 is a plan view of the configuration shown in FIG. The gravure engraving machine includes a bed 1, a headstock 2 fixed to the upper surface of the bed 1, a tailstock 3 arranged to face the headstock 2, and a table 4.
The tailstock 3 is movable in the left-right direction of the apparatus along a pair of guide rails 6 arranged on the upper surface of the bed 1.
The tailstock 3 can be moved toward or away from the headstock 2 by a drive mechanism 9 including a motor and a belt provided on the side of the bed 1. The tailstock 3 is
Quill 12 for holding one end of gravure cylinder C
Is equipped with. The quill 12 is adapted to be retracted by the action of the cylinder 13.

The table 4 is movable left and right along a pair of guide rails 7 arranged on the upper surface of the bed 1. The table 4 includes a ball screw 15 arranged between a pair of rails 7 and a drive motor 1 for driving the ball screw 15.
A movable body 6 can be moved in the left-right direction along the rail 7 by the rail 6. The headstock 2 includes a spindle 10 that holds the end of the gravure cylinder C opposite to the tailstock 3.
The main shaft 10 is rotated by a drive mechanism 11 including a drive motor and a belt. In such a structure, the gravure cylinder C is supported between the main shaft 10 and the quill 12 as shown by the chain double-dashed line in FIG. It

An engraving head 21 is provided on the table 4 so as to be movable in the front-rear direction of the apparatus. A guide rail 20 is provided on the upper surface of the table 4, and the ball screw 2
The engraving head 21 can be displaced back and forth by a drive mechanism including the drive motor 23 and the drive motor 23. FIG. 3 is a perspective view showing a stylus provided on the engraving head 21 and a drive mechanism thereof. The stylus holder 30 is fixed to the tip of a torsion shaft 31 provided upright on the fixing portion 33. A stylus 32 made of a diamond tool is fixed to one end of the stylus holder 30. A diamond-shaped rotor 34 in a plan view is fixed to an intermediate portion of the torsion shaft 31. A laminated magnetic body (stator) 35 is arranged around the rotor 34 so as to sandwich the rotor 34. A permanent magnet 36 for applying a magnetic force to the stator 35 is arranged on the side of the stator 35. Further, a coil 37 is arranged between the rotor 34 and the stator 35 so as to surround the rotor 34. When the engraving signal (current signal) is applied to the coil 37, the stylus holder 30 vibrates in the direction of arrow B in the figure according to the frequency of the engraving signal. In this way, the torsion shaft 31, the rotor 34, the stator 3
A driving means for driving the stylus 32 is configured by the coil 5, the coil 37, and the like.

FIG. 4 is a block diagram showing the electrical construction of this apparatus. The gravure engraving machine 100 is connected to a data creation device 201 composed of a personal computer or the like. That is, the data creation device 201
CPU201A, ROM201B, RAM201C
Including and The data creating device 201 includes a reading device 202 such as a scanner, another image system 203,
An external storage device 204 such as a hard disk device and an operation unit 205 such as a keyboard and a mouse are connected.

The data creating device 201 is an external storage device 2.
The program stored in 04 is stored in the RAM 20 as necessary.
It can be read into 1C and operated according to this program. In this way, the data creation device 201
Image data for gravure plate making can be created based on data read from a predetermined document by the reading device 202 or data obtained from other image system 203. For example, the data creation device 201 obtains the offset image data from another image system and performs offset / gravure conversion to create the image data.

The operator operates the operation unit 205 to instruct the data creating device 201 of various data or instructions (for example, the number of lines, cell pattern (elongate, compressed, etc.), single engraving / double engraving, etc. Enter the engraving conditions including). Based on the input data or instructions from the operation unit 205, the data creation device 201 generates carry instruction data, sub-scanning instruction signal, and main scanning instruction signal together with the image data. These data and signals are provided to the gravure engraving machine 100.

The gravure engraving machine 100 includes a data correction unit 1
10, a density signal generator 101, a carry signal generator 102, a sub-scanning motor 103, and a main scanning motor 104.
The adder 105, the engraving head 21, the sub-scanning motor 107, and the main scanning motor 108. The data correction unit 110 includes an arithmetic unit including a CPU 110A, a ROM 110B, and a RAM 110C, and creates image data that has been corrected to compensate for hysteresis of stylus displacement.

The density signal generator 101 is a data correction unit 1.
A density signal is generated on the basis of the image data given from 10. The carry signal generation unit 102 determines the amplitude and the offset amount based on the carry command data provided from the data creation device 201, and generates the carry signal. The density signal from the density signal generator 101 and the carry signal from the carry signal generator 102 are added by the adder 1
After being added at 05, it is applied to the engraving head 21 as an engraving signal.

The sub-scanning motor 107 is a motor for moving the engraving head 21 in the sub-scanning direction. The main scanning motor 108 is a motor for rotating the gravure cylinder 14. The sub-scanning motor control unit 103 controls the engraving head 21 according to the difference in the number of lines, the engraving once, and the engraving twice.
Data generator 2 for changing the feed amount of the sub-scanning direction
01 based on the sub-scanning command signal from the sub-scanning motor 1
Control 07. The main scanning motor control unit 104 changes the rotation speed of the gravure cylinder 14 according to the difference in the cell pattern and the number of lines, and thus controls the main scanning motor 108 based on the main scanning command signal from the data creation device 201. .

A cell monitor 40 for observing the shape of the cells formed on the cylinder surface facing the surface close to the side end of the gravure cylinder C arranged between the headstock 2 and the tailstock 3. Are arranged. Cell monitor unit 40
Is, for example, an optical microscope and a CCD connected to it.
It is provided with an element and can freely move toward and away from the gravure cylinder C. The cell monitor unit 40 captures an image of the surface of the gravure cylinder C, generates a video signal corresponding to the captured image, and inputs the video signal to the image processing unit 41.

The image processing section 41 calculates the cell shape based on the video signal from the cell monitor section 40. And
A table required for data correction processing in the data correction unit 110 is created based on the calculation result and stored in the table memory 50. The table memory 50 is preferably composed of a writable non-volatile memory such as RAM or EEPROM with a backup power supply. The data correction unit 11 refers to the table in the table memory 50 and corrects the data.

FIG. 5 (c) shows the waveform of the engraving signal applied to the engraving head 21, which corresponds to the stylus displacement waveform. This signal waveform is obtained by superposing the density signal waveform as shown in FIG. 5 (b) on the high frequency carry signal waveform as shown in FIG. 5 (a) (that is, modulating the carry signal with the density signal). It is a thing. By applying such an engraving signal to the engraving head 21, cells having a depth and a width (area) corresponding to the density signal can be engraved on the surface of the gravure cylinder C. Note that FIG.
The chain double-dashed line R in (c) corresponds to the surface of the gravure cylinder C, and the hatched portion in the figure corresponds to the cell.

As described above, the displacement of the stylus 32 exhibits a hysteresis characteristic with respect to the drive current input to the engraving head 21. The stylus 32 vibrates based on the engraving signal, and the Lissajous figure on the drive current-displacement plane is as shown in FIG.
Focusing on the neutral position of the displacement of the stylus 32 (meaning the central position of the vibration and corresponding to the central position of the vibration of the engraving signal on which the carry signal is superimposed), the relationship between the neutral position and the drive current is It is within the shaded area in FIG. Since the density signal created based on the image data is nothing but the signal that determines the neutral position, to correct the hysteresis characteristic, based on the behavior of the neutral position,
The image data may be corrected.

FIG. 7 is a diagram for explaining the hysteresis characteristic of the stylus displacement in more detail. The displacement of the stylus 32 when a drive current with which the carry signal is not superimposed is given (hereinafter, simply referred to as "the stylus 32 Displacement)) and the drive current. In FIG. 7, the origin of displacement of the stylus 32 is set at a reference position having a predetermined relationship with the surface of the gravure cylinder C. The stylus 32 forms deeper cells on the surface of the gravure cylinder C as the displacement increases.

As the current is increased, the stylus 32
The relationship between the displacement and the current follows the path P1 and reaches the point S1. The point S1 corresponds to the displacement of the stylus 32 when the stylus 32 engraves the maximum size cell. Point S1
As the current is reduced from, the relationship between the displacement and the drive current follows the path P2 and reaches S2. The point S2 corresponds to the displacement of the stylus 32 when the tip of the stylus 32 is farthest from the surface of the gravure cylinder C.

On the other hand, if the drive current is decreased before reaching the point S1 or is increased before reaching the point S2, the relationship between the displacement and the drive current is a straight line with a constant inclination. Follow a specific path. That is, for example, it moves on the paths P3, P4, and P5. The paths P3, P4 and P5 are parallel to each other. For example, when the path P3 is traced when the drive current decreases, and the width of decrease in the current is sufficiently large, the path P3 moves to the path P2. Similarly, when the path P3 is followed when the drive current increases,
When the amount of increase in current is sufficiently large, the process moves from the path P3 to the path P1.

Further, for example, when the drive current slightly decreases and then increases again while the relationship between the displacement and the current is changing along the path P1, the path P2 moves to the path P2 as shown by the path P4. Turn back on the way before doing. If the drive current slightly increases and then decreases again while following the path P2, the drive current is returned before the transfer to the path P1 as shown by the path P5.

FIG. 8 is a diagram for explaining the principle of data correction by the data correction unit 110. A suitable displacement of the stylus 32 with respect to the current value I is Yo. But,
If the stylus displacement follows the path P1,
The actual displacement of the stylus 32 is Y1, and if the path P2 is followed, the actual displacement of the stylus 32 is Y2. Further, if the path P3 is being followed, the actual displacement of the stylus 32 is Y3.

If the relationship between the drive current and the displacement of the stylus 32 follows the path P1, increasing the drive current to I1 will achieve the proper displacement Yo. Similarly, if the relationship between the drive current and the displacement of the stylus 32 follows the path P2, then by reducing the drive current I to I2, an appropriate displacement Yo is achieved. Furthermore, if the relationship between the drive current and the displacement of the stylus 32 follows the path P3, the drive current I3 will achieve an appropriate displacement Yo.

Since the relationship between the actual displacement of the stylus 32 and the driving current is almost the same as the intermediate path such as the path P3 between the paths P1 and P2, the path P3 will be considered further. The target displacement with respect to the drive current is given by the target curve Lo between the path P1 and the path P2. If the point representing the relationship between the drive current and the actual displacement of the stylus 32 is below the target curve Lo on the path P3, the target displacement Yo can be obtained by increasing the current. Further, if it is above the target curve Lo, the target displacement Yo can be obtained by reducing the current.

Therefore, a state variable S representing the position between the path P1 and the path P2 where the point representing the relationship between the driving current and the displacement of the stylus 32 is introduced. That is, the state variable S is S = 1 on the path P1,
On the route P2, S = -1. Route P1 and route P
In the middle between 2 and 1, -1 <S <1, and the target curve L
On S, S = 0. The sign of S indicates whether the current should be increased (positive sign) or the current should be decreased (negative sign). The state variable S eventually corresponds to the degree of error in the displacement of the stylus 32 with respect to the target displacement.

Since the target displacement Yo exists on the curve of S = 0 (target curve Lo), the value of S and the hysteresis amount (the current value on the path P1 and the current value on the path P2 for a certain displacement are An appropriate correction amount can be calculated by the hysteresis current width H corresponding to ½ of the difference (1).
However, the actual hysteresis current width H is usually smaller than that shown in FIG. 8 because the carry signal is superimposed on the engraving signal.

Between the route P1 and the route P2, the route P3
There are innumerable intermediate paths such as, and these paths are parallel to each other. In order to apply an appropriate correction to the image data to compensate for the hysteresis, it is necessary to specify on which path the relationship between the drive current and the displacement of the stylus 32 is. Therefore, when the cell size is changed, history data is created based on the image data corresponding to the plurality of cells immediately before.

A more specific description will be given. First, the k-th uncorrected image data in the main scanning direction (k = 1, 2, 3, ...) Is set to ncd (k), and the corrected image data is cd.
(K). In this case, the history data is given by the following equation (1).

[0044]

[Equation 1]

AV is the number of data to be referred to. The weighting coefficient α _i may be a different value for each i, or may be an equal value for all i. If all α _i are set to “1”, the average value of the corrected data corresponding to the AV cells (for example, 3 cells) immediately before the cell to be corrected becomes the history data. From the viewpoint of simplifying the calculation, it is preferable to obtain the average value as the history data.
The data of the immediately preceding one or two cells can be adopted as the history data, but it is not preferable because it may be affected by a sudden change in concentration and the reverse correction may be performed. For example, USM (UnSh
There is a case where processing such as arp Mask) processing is performed to emphasize the edge portion of the image, or a high density portion or a low density portion suddenly exists in the tint image portion. However, such a sudden concentration change has a small contribution to the hysteresis and a large contribution from the tendency of the concentration in a wider region. That is, the change in the state variable S due to the sudden change in concentration is so small that it can be ignored. Therefore, if the data of one cell immediately before is used as the history data, there is a possibility that appropriate correction cannot be performed. AV
If 4 is 4 or more, it takes a long time to calculate the history data, which is not preferable.

When the history data is obtained as described above,
State variable S used to correct the data in the kth cell
_k is calculated by the following equation (2). In the equation (2), DM is a data change amount necessary for a transition to occur between the route P1 and the route P2, as shown in FIG.

[0047]

[Equation 2]

That is, the result of subtracting the history data from the data of the kth cell is divided by DM / 2 for normalization,
By adding to the previous state variable S _k-1, the state variable S _k corresponding to the k th cell is determined. That is,
The state variable S changes according to the amount of change from the history data. However, a 1 when S _k (or S _k-1) is 1 or more, when S _k (or S _k-1) is less than -1 and -1.

Using the state variable S _k thus obtained,
The corrected data cd (k) is calculated according to the following equation (3). The second term of the equation (3) corresponds to the correction amount. cd (k) = ncd (k) + SA × S _k × H (3) That is, the value obtained by multiplying the product of the state variable S _k and the hysteresis current width H by the fine adjustment coefficient SA is corrected. Previous data ncd
By adding to (k), the corrected data cd
(K) is calculated. Therefore, the larger the absolute value of the state variable S _k, the larger the correction range of the data. Also,
The data will be increased or decreased depending on the sign of the state variable S _k . As described with reference to FIG. 8, the state variable S has a larger absolute value as the point representing the relationship between the displacement of the stylus 32 and the drive current is further away from the target curve Lo, and is located above or below the target curve Lo. It takes a different sign depending on whether it is on the side. From this, it is understood that the above correction is appropriate.

The fine adjustment coefficient SA is a coefficient for finely adjusting the correction amount according to the sign of the state variable S, and takes a different value depending on the sign of S. This is S> 0
It has been experimentally confirmed that it is preferable to make the data change width different for correction in the case of (when data should be increased) and in the case of S <0 (when data should be decreased). Because. Specifically, in the case of S> 0, it is preferable to use the coefficient SA having a larger value than in the case of S <0. The reason seems to be that the cutting resistance increases when the data is increased to increase the size of the cell, whereas the cutting resistance decreases when the data is decreased to decrease the size of the cell.

FIG. 9 is a diagram for explaining in more detail the principle of data correction according to the equation (3), and is an enlarged view near the path P3 in FIG. For example, it is assumed that the relationship between the driving current corresponding to the image data before correction and the displacement of the stylus 32 is represented by a point nx. Then, it is assumed that the target displacement is exactly achieved by increasing the image data by the amount corresponding to the hysteresis current amount H. At this time, the following expression (4) is established for the state variable S _k at the point nx.

[0052]

[Equation 3]

That is, the correction amount becomes H when S _k = 1- (2H / DM). On the other hand, since the data correction amount is zero when S _k = 0 and is proportional to S _k , the following equation (5) is satisfied after all.

[0054]

[Equation 4]

In the equation (5), sa is a fine adjustment coefficient which takes different values when S _k is positive and when it is negative. The fine adjustment coefficient sa and the denominator of the equation (5) are collectively replaced by the fine adjustment coefficient SA as in the following equation (6) to obtain the above equation (3).

[0056]

[Equation 5]

FIG. 10 is a diagram showing an example of the situation of displacement of the stylus 32. A curve D11 represents the locus of the tip of the stylus 32 when the state in which a shallow cell is formed is changed to the state in which a deep cell is formed. If the influence of hysteresis is not eliminated, the locus of the tip of the stylus 32 follows the curve D11n indicated by the broken line. On the other hand, when an engraving signal is created using the image data corrected by the present embodiment, the tip of the stylus 32 draws a solid line locus, and a cell of a desired size is formed. .

The curve D12 represents the locus of the tip of the stylus 32 when the state where a deep cell is formed is changed to the state where a relatively shallow cell is formed. A curved line D12n represented by a broken line represents a locus of the tip of the stylus 32 when the influence of hysteresis is not eliminated. 11 and 12 are flowcharts for explaining the data correction processing by the data correction unit 110. This correction processing is realized by the CPU 110A operating according to a predetermined program stored in the ROM 110B.

When the image data is given from the data creating device 201, the image data is temporarily stored in the RAM 110C. Then, first, a variable n corresponding to the number of lines
The initial value "1" is assigned to (step Q1), and RAM1
The data of the n-th line (first line) in 10C is taken out (step Q2). The hysteresis correction calculation shown in FIG. 12 is performed on the data of the nth line (step Q3), and the corrected data is created. The corrected n-th line data is stored in a predetermined area in the RAM 110C (step Q4).

The same process is performed for all lines while incrementing the variable n (step Q6) (step Q5). When the corrected image data is obtained for all the lines, the data correction processing is ended, and the corrected image data is sequentially given to the density signal generation unit 101. As a result, an engraving signal corresponding to the corrected image data is applied to the engraving head 21.

The hysteresis correction calculation procedure will be described with reference to FIG. First, a variable k indicating which cell in one line corresponds to "1" is initialized, and further, a state variable S is initialized to "1" (step Q3).
1). Before the sculpture started, the stylus 32
It is in the retracted position where it does not contact the gravure cylinder C. When engraving, the engraving signal (driving current) is increased,
The stylus 32 reaches a state where the gravure cylinder C is engraved. Therefore, the relationship between the displacement of the stylus 32 and the drive current follows the path P1 in FIG. Therefore, it can be seen that it is appropriate to set the initial value of S to "1".

Next, it is judged whether the data before correction is equal to the data before correction of the cell immediately before (step Q32). When engraving the first cell, there is no previous data. However, as described above, since the stylus 32 is held at the position retracted from the surface of the gravure cylinder C, the previous data is regarded as zero and the processing is performed.

If it is not equal to the data of the immediately preceding cell, then the state variable S used for correcting the kth (first is the first) data is calculated (step Q33). That is, the previous state variable S is regarded as S _k−1, and the state variable S _k calculated according to the above equation (2) is changed to the new state variable S _k.
Becomes By the way, in order to calculate the history data of the equation (1), the corrected data of the immediately preceding AV cells are required. However, before the calculation of the first AV pieces of data is completed, there are only less than AV pieces of data. Therefore, if the corrected data that can be used to calculate the history data is less than AV, it is considered that the missing data are all zero,
Processing is performed. The suitability of this treatment is understood by considering that the stylus 32 has been retracted from the surface of the gravure cylinder C before engraving the first cell.

When the state variable S is obtained, an appropriate value of the fine adjustment coefficient SA is set based on the sign of the state variable S (step Q34). That is, the first fine adjustment coefficient SA1 or the second fine adjustment SA2 (SA1> SA2) is set to the coefficient SA depending on whether the correction is to increase the current or decrease the drive current. Used as. The coefficients SA1 and SA2 are stored in the table memory 5
0 is stored in advance.

Then, the corrected data cd (k) is calculated according to the above equation (3) (step Q35). The parameters DM and H necessary for this calculation are also stored in the table memory 50 in advance. Step Q32
In the case where the image data of the cell immediately before and the image data of the cell to be processed are the same, in step Q33.
And the processing of Q34 is omitted. That is, the corrected data is calculated by using the state variable S and the fine adjustment coefficient SA that have been used. If there is no change in the image data,
This is because it is not necessary to change the state variable S. In this way, the image data is corrected based on the history before the last change of the image data.

The above-mentioned processing is executed for all cells forming one line while incrementing the variable k (step Q37) (step Q36). The parameters SA1, SA2, DM and H are different for each engraving head and are different according to the type of carry signal. For example, when forming fine cells with high density, a carry signal of small amplitude and high frequency is used,
A large amplitude carry signal is used to form a large cell with a relatively low density. Therefore, as shown in FIG. 13, the carry signal C is stored in the table memory 50.
The values of the parameters SA1, SA2, DM and H are stored for each of C1, C2 and C3.
Reads the value corresponding to the carry signal to be used and uses it for data correction.

Next, a method of determining the parameters SA1, SA2, DM and H to be stored in the table memory 50 will be described. FIG. 14 is a diagram showing an example of a test pattern image formed to determine a parameter. In FIG. 14, the magnitude of the density is represented by the density of diagonal lines. The high concentration region is configured by arranging large cells, and the low concentration region is configured by arranging small cells.

A plurality of test pattern images TP1, TP2, TP3, ... Corresponding to a plurality of types of carry signals.
.. is formed. Each test pattern image TPj (j =
, 1, 2, 3, ...) include two rows of image portions R1 and R2 along the engraving direction. Each image part R1 and R
2 has a plurality of density portions each having a density that varies stepwise. More specifically, the image portion R1 of the first column
Has a plurality of density portions from the high density portion to the low density portion and again to the high density portion. The image portion R2 of the second column is
It has a plurality of image parts from the low density part to the high density part and then to the low density part again.

The test pattern image is the gravure cylinder C.
In parallel with the engraving of the test pattern image or after the engraving of the test pattern image on the gravure cylinder C is completed, the cell monitor unit 40 (see FIG. 4) functions to capture the image of the cells forming the test pattern image. To be done. And
The image processing unit 41 detects the cell width of each density portion. The image processing unit 41, based on the detected cell width,
Create a hysteresis curve as shown in Figure 8, and
The hysteresis current width H and the data width DM corresponding to the current width required for the state transition between the path P1 and the path P2 are obtained. In this way, the parameters H and DM corresponding to a plurality of carry signals are automatically obtained and written in the table memory 50.

When the parameters H and DM are obtained, a test pattern image is formed again using the data corrected according to the flow charts of FIGS. 11 and 12 using these parameters. Then, the cell width is obtained in the same manner as in the above case. Image processing unit 4
1 calculates the difference between the target cell width and the actual cell width,
A fine adjustment coefficient SA1 corresponding to the case of increasing the current,
A fine adjustment coefficient SA2 corresponding to the case where the current is reduced is calculated and written in the table memory 50.

As described above, according to the present embodiment, the image data corrected to compensate the hysteresis of the stylus displacement is created based on the history before the change of the image data. Therefore, by applying the engraving signal generated based on the corrected image data to the engraving head 21, the displacement of the stylus 32 can be accurately controlled to the target displacement. As a result, it becomes possible to form a high-quality image without density unevenness.

Next, a second embodiment for controlling the displacement of the stylus 32 more accurately will be described. In the description of this embodiment, each of the above-mentioned drawings will be referred to again. In the above-described first embodiment, two types of fine adjustment coefficients SA1 or SA2 are used depending on whether to increase or decrease the image data for correction.
However, it has been experimentally confirmed that it is better to apply different fine adjustment coefficients depending on whether the route P1 or the route P3 shown in FIG. 8 is passed when performing the correction for increasing the current value. There is. The same applies when reducing the current value, and it is preferable to make the fine adjustment coefficient different depending on whether the current passes through the path P2 or the path P3. The reason is that the paths P1 and P2 are paths corresponding to the upper limit or the lower limit of the displacement of the stylus 32 with respect to each current value, whereas the path P3 is an intermediate between the upper limit and the lower limit of the displacement of the stylus 32. It is presumed that it is at a point corresponding to.

More specifically, it is necessary to consider the following 6 cases depending on cases. When corrected only through P1. When corrected only through P2. Corrected through P3 only and S _k is positive.

When the correction is performed through P3 only,
If S _k is negative. When correction is performed across P3 and P1. When correction is performed across P3 and P2. The above cases and will be described with reference to FIG. For example, it is assumed that the point A1 corresponding to the history data obtained according to the equation (1) is on the path P2. Then, it is assumed that the point corresponding to the image data before correction is A2. At this time, the state variable is S _k = −1, and theoretically, the corrected data may be obtained by reducing the image data by the hysteresis current width H. In FIG. 15, point D
Corresponds to the corrected image data.

On the other hand, it is assumed that the point B1 corresponding to the history data obtained according to the equation (1) is on the path P3.
Then, it is assumed that the point corresponding to the image data before correction is B2. At this time, for example, S _k = −0.5, and theoretically, the corrected image data may be obtained by reducing the image data by the hysteresis current width H. In this case, the point D corresponds to the corrected image data.

In each of the above two cases, the image data needs to be reduced by the hysteresis current value H, but the route to the corrected point D is different. That is, on the other hand, only the route P2 is passed and A2 →
While following a path such as C → D, the other is path 3
And a route such as B2 → C → D across the route 2 and the route 2. Due to the difference in the path, it is necessary to make the correction amount different in order to accurately control the displacement of the stylus 32.

More specifically, the uncorrected data ncd
(k), the amount of hysteresis current H and the above-mentioned parameter D
The corrected data cd (k) is calculated by using M in each of the above cases. The calculation formula is as follows. When correction is performed through P1 only (when S _k = 1). cd (k) = ncd (k ) + sa 1 × S k × H = ncd (k) + sa 1 × H ····· (3-1) When corrected through P2 only (S _k = -1 When).

Cd (k) = ncd (k) + sa ₂ × S _k × H = ncd (k) −sa ₂ × H (3-2) Of the cases where correction is performed only through P3, When S _k is positive. (When 0 <S _k <1- (2H / DM))

[0079]

[Equation 6]

When S _k is negative out of the case where correction is performed only through P3. (When -1+ (2H / DM) <S _k <0)

[0081]

[Equation 7]

When correction is performed across P3 and P1. (When 1- (2H / DM) <S _k <1) cd (k) = ncd (k) + sa ₃ × (+1) × {(1- | S _k |) × (DM / 2)} + sa ₁ × (+1) × {H− (1− | S _k |) × (DM / 2)} (3-5) When correction is performed across P3 and P2.

(When -1 <S _k <-1+ (2H / DM)) cd (k) = ncd (k) + sa ₄ × (-1) × {(1- | S _k |) × (DM / 2)} + sa ₂ × (-1) × {H- (1- | S _k |) × (DM / 2)} (3-6) The above equation (3-1), the equation (3-1) Formula 3-2), Formula (3-3), Formula (3-4)
In equation (3-5) and equation (3-6), sa ₁ is a fine adjustment coefficient when data correction is performed through the path P1, and sa ₂ is data correction through the path P2. Is a fine adjustment coefficient when it is made, sa ₃ is a fine adjustment coefficient corresponding to the case where the data is increased by the correction through the path P3, and sa ₄ is a fine adjustment coefficient when the data is decreased by the correction through the path P3. It is the corresponding fine adjustment coefficient. However, sa
₁ > sa ₂ is preferable, and sa ₃ > sa
₄ is preferable. It is as described above that the reason is estimated to be due to the cutting resistance when engraving the cell.

The equation (3-1) indicates that, in the case of the correction that follows the path P1, it is sufficient to increase the data by the correction amount obtained by multiplying the hysteresis current amount H by the fine adjustment coefficient sa ₁ . Further, the expression (3-2) indicates that, in the case of the correction that follows the path P2, the data may be reduced by the correction amount obtained by multiplying the hysteresis current amount H by the fine adjustment coefficient sa ₂ . The formula (3-3) and the formula (3-4) are as described in the first embodiment.

The equation (3-5) will be described with reference to FIG. Referring to FIG. 16, when the point corresponding to the image data before correction is on the path P3 and the following expression (7) is satisfied for the state variable S _k corresponding to the image data, the path P3 and the path P3 It is understood that the correction across P1 (or path P2) is made. (1- | S _k |) × (DM / 2) <H (7) When this equation (7) is solved for | S _k |, the following equation (8) is obtained.

| S _k |> 1- (2H / DM) (8) Therefore, the following (a), (b) and (c) are understood. When (a) -1+ (2H / DM) <S _k <1- (2H / DM),
It is corrected through only the path P3. (b) When 1− (2H / DM) <S _k <1, it is corrected across the paths P3 and P1.

(C) When -1 <S _k <-1+ (2H / DM), the correction is performed across the paths P3 and P2. The case of (b) above will be further considered with reference to FIG. It is understood from FIG. 16 that the correction amount is theoretically equal to the hysteresis current amount H. However, the breakdown of the correction amount in this case corresponds to the path P3 for the portion (1- | S _k |) × (DM / 2), and the remaining H- (1
The portion of − | S _k |) × (DM / 2) corresponds to the path P1. Therefore, the portion corresponding to the route P3 is multiplied by the fine adjustment coefficient sa _3, and the portion corresponding to the route P1 is adjusted
Multiply by a ₁ and the addition result is used as the correction amount. As a result, the above equation (3-5) is obtained. sa ₁ = sa ₃ = 1
Then, the correction amount becomes H which is a theoretical value.

Equation (3-6) can be similarly derived.
Wear. Gravure engraving to achieve the above correction
The data correction unit 110 of the engraving machine 100 uses the state variable S_kThe value of the
According to the above formula (3-1), formula (3-2), formula (3-3),
Formula (3-4), Formula (3-5) or Formula (3-6)
One of them is selected and the corrected image data is calculated. this
Fine adjustment coefficient sa used in the calculation₁~ Sa _FourNavi
Other parameters DM and H are for the table memo.
It is stored in advance in the memory 50. In table memory 50
The table of the test table is the same as the case of the first embodiment.
Engraving the pattern image and engraving with the cell monitor 40.
Image by monitoring the size of the engraved cells
It is automatically created by the operation of the processing unit 41.

As described above, according to the present embodiment, an appropriate fine adjustment coefficient is selected in accordance with the path along which the image data is corrected on the current-stylus displacement plane, and the path is corrected. An appropriate correction calculation formula corresponding to is applied. Therefore, the displacement of the stylus 32 can be controlled extremely accurately. As a result, by using the gravure cylinder C after the engraving process, it is possible to obtain a high-quality printed matter without density unevenness.

The present embodiment has been described above, but the present invention is not limited to the above embodiment. For example, in the above embodiment, the gravure engraving machine 1
Although the data correction processing for compensating for the hysteresis is performed in the data correction unit 110 provided in No. 00, it goes without saying that such correction may be performed on the data creation device 201 side. That is, a program for data correction may be loaded into the RAM 201C of the data creating device 201 and the data creating device 201 may be operated according to this program. In this case, since the corrected data is input to the gravure engraving machine 100,
The gravure engraving machine 100 may have a conventional configuration without the data correction unit 110. In addition, in the case of such a configuration, the parameter table is used as the data creation device 2
Need to be available at 01. Therefore, a table of parameters obtained in advance is stored in, for example, the external storage device 204, and the data creation device 201
Should refer to this if necessary.

In the above embodiment, the corrected image data is input to the density signal generator 101 after the corrected data for all the cells of one image are created. For example, the corrected image data of each line may be sequentially applied to the density signal generation unit 101 every time the corrected image data of one line is obtained. In order to realize such processing, steps Q4 and Q4 in FIG.
Between the process of 5 and the process of 5, the process of giving the data of the nth line to the density signal generating unit 101 may be added.

Furthermore, in the above embodiment, an example in which an image is formed by a plurality of lines has been described. That is, each time one line image is formed,
The engraving head 21 is intermittently fed in the sub-scanning direction, whereby a plurality of lines are formed on the surface of the cylinder C.
However, the present invention is applicable not only to such an engraving method by intermittent feeding but also to a so-called spiral engraving method. In the spiral engraving method, the engraving head 21 is slowly and continuously fed in the sub-scanning direction, and the engraving head 21 scans the gravure cylinder C in a spurious manner. That is, an image is formed by one line. In this case, the data correction unit 1
The data correction processing in 10 may be performed collectively for all image data, or may be performed in units of a fixed amount of image data using, for example, a FIFO (first in, first out) memory.

In the above embodiment, the parameter table is automatically created, but the parameter table may be created by an operator. Furthermore, in the above embodiment, the case where the engraving head is driven by current has been described, but an engraving head driven by voltage may be used. In this case, the image data is corrected based on the relationship between the voltage and the displacement of the stylus.

Besides, it is possible to make various design changes within the scope of the technical matters described in the claims.

[0095]

According to the present invention, since the influence of the stylus displacement hysteresis is eliminated, it is possible to surely engrave a cell of a desired size in the gravure cylinder. Therefore, the printed matter obtained by using the engraved gravure cylinder is of high quality with no density unevenness.

Further, as described in claim 3, if the history data is calculated based on the corrected image data corresponding to the plurality of cells before the image data is changed, the contribution to the hysteresis is achieved. It is possible to eliminate the influence of a sudden change in data. Thereby, the displacement of the stylus can be controlled more accurately. further,
When the value of the image data is increased and when the value of the image data is decreased as described in claim 5, the stylus displacement is targeted when increasing or decreasing the value of the image data. The value of can be precisely controlled.

[Brief description of drawings]

FIG. 1 is a front view showing a configuration of a gravure engraving machine to which an embodiment of the present invention is applied.

FIG. 2 is a plan view of the configuration shown in FIG.

FIG. 3 is a perspective view showing the internal structure of part of the engraving head.

FIG. 4 is a block diagram for explaining an electrical configuration of a gravure engraving machine.

FIG. 5 is a waveform diagram of a carry signal (a), a density signal (b) and an engraving signal (c).

FIG. 6 is a diagram showing a region where a relationship between a neutral position of a stylus and a drive current can be taken. "

FIG. 7 is a diagram for explaining a hysteresis characteristic of displacement of a stylus.

FIG. 8 is a diagram for explaining the principle of data correction for compensating for hysteresis.

FIG. 9 is a diagram for explaining a detailed principle of data correction.

FIG. 10 is a diagram showing a trajectory of a tip of a stylus.

FIG. 11 is a flowchart illustrating a data correction process.

FIG. 12 is a flowchart illustrating a hysteresis correction calculation process.

FIG. 13 is a diagram for explaining the contents of a table used for hysteresis correction calculation.

FIG. 14 is a diagram showing an example of a test pattern image for obtaining a parameter necessary for a hysteresis correction calculation.

FIG. 15 is a diagram for explaining the principle of data correction according to the second embodiment of the present invention.

FIG. 16 is a diagram for explaining the principle of data correction according to the second embodiment.

FIG. 17 is a diagram showing the relationship between stylus displacement and applied current when a static current is applied to the engraving head.

FIG. 18 is a diagram showing a Lissajous figure corresponding to the case where an engraving signal in which a carry signal is superimposed is applied to the engraving head.

FIG. 19 is a diagram showing a locus of stylus displacement affected by hysteresis.

FIG. 20 is a diagram illustrating an example of image deterioration due to the influence of hysteresis.

FIG. 21 is a diagram showing an example of image deterioration due to the influence of hysteresis.

[Explanation of symbols]

21 engraving head 30 stylus holder 31 torsion shaft 32 stylus 34 rotor 35 stator 37 coils 40 cell monitor 41 Image processing unit 50 table memory 100 gravure engraving machine 101 concentration signal generator 102 carry signal generator 110 Data correction unit 201 Data creation device 204 external storage device

Claims (6)

(57) [Claims] 1. A device for controlling the displacement of a stylus for engraving a cell on the surface of a gravure cylinder, the history calculating means for obtaining a history of displacement of the stylus, and the history obtained by the history calculating means. A correction amount calculation means for calculating a correction amount for canceling the hysteresis of the stylus displacement based on the target displacement, and an engraving signal for displacing the stylus based on the correction amount calculated by the correction amount calculation means. And a stylus displacement control device. 2. The correction means corrects the image data corresponding to the target displacement based on the correction amount calculated by the correction amount calculation means, and creates corrected image data. The stylus displacement control device according to claim 1, further comprising means for creating an engraving signal based on the subsequent image data. 3. The history calculation means calculates the history data based on each corrected image data corresponding to a plurality of cells before the image data is changed. Stylus displacement control device. 4. The correction amount calculation means includes means for calculating a state variable corresponding to the error of the stylus displacement with respect to the target displacement based on the history data and the state variable before the image data changes. The stylus displacement control device according to claim 3, wherein. 5. The correcting means corrects the image data with a value obtained by multiplying the correction amount calculated by the correction amount calculating means by a fine adjustment coefficient, and a first means for increasing the value of the image data. When the fine adjustment coefficient is applied as the fine adjustment coefficient and the value of the image data is reduced, the second fine adjustment coefficient smaller than the first fine adjustment coefficient is used.
5. The stylus displacement control device according to claim 1, further comprising means for applying the fine adjustment coefficient of 1. as the fine adjustment coefficient. 6. An engraving head provided with a driving means driven by an engraving signal, and a stylus engraving a cell on the surface of a gravure cylinder by being driven by the driving means, and the engraving head according to claim 1. A stylus displacement control device according to claim 1.