JP2766167B2 - Laser plate making equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser plate making apparatus suitable for use in plate making of an original plate for gravure printing.

[0002]

2. Description of the Related Art Gravure printing, which is known as a type of relief printing, is used for printing a large number of copies of photographic images on paper at high speed. As a means for producing an original (intaglio) plate for performing gravure printing, an electronic gravure plate making apparatus using a semiconductor laser has been developed.

FIG. 6 shows an example of a conventional electronic gravure plate making apparatus using a semiconductor laser. In FIG. 6, 10
1 shows an intaglio plate making apparatus as a whole, and this plate making apparatus 10 includes a plate cylinder 12 which is rotated by driving by a plate cylinder rotating motor 11. The plate cylinder 12 has a cylindrical shape, and a plate sheet 13 is wound on a side surface. In this case, the plate sheet 13 is made of a thermoplastic resin such as a polyethylene resin, and its end is fixed to the side surface of the plate cylinder 12 by the clamping plate 14.

A laser beam from an optical block 15 is applied to the side surface of the plate cylinder 12 around which the plate sheet 13 is wound. That is, a ball screw 16 is disposed parallel to the rotation axis of the plate cylinder 12, and the optical block 15 is attached to the ball screw 16. Then, by rotating the ball screw 16 by the laser block moving motor 17, the position of the optical block 15 moves parallel to the rotation axis of the plate cylinder 12.

The plate cylinder 12 is rotated by the plate cylinder rotating motor 11 while moving the optical block 15 in the axial direction, so that the laser beam emitted from the optical block 15 Are sequentially scanned, and FIG.
Are formed on the surface of the plate sheet 13 as shown in FIG.

Here, if the output state of the laser beam from the optical block 15 is controlled in accordance with the image to be made, the recess formed in the plate sheet 13 corresponds to the image. That is, the rotary encoder 2 is
0, and the rotary encoder 20 attaches the plate cylinder 12
The rotational position is detected and supplied to a central control unit (CPU) 21. A RAM 22 in which image data is stored is connected to the central control device 21, and the image data is sequentially read from the RAM 22 in synchronization with the rotation position detection data, and the read image data is transferred to the central control device 21 via a gamma conversion circuit 23. This is supplied to the laser driver 24. Then, the semiconductor laser in the optical block 15 is driven by the laser driver 24 according to the image data, and a concave portion corresponding to the image is formed on the surface of the plate sheet 13, thereby performing plate making of an original plate (intaglio plate).

[0007] When making an original plate by using such a laser plate making apparatus, it is necessary to irradiate a laser beam in a state where the surface of the plate sheet 13 serving as the original plate is accurately focused. That is, it is necessary to adjust the focus of the laser beam output from the semiconductor laser in the optical block 15 by the focus lens in the optical block 15 to focus on the surface of the plate sheet 13. As the focus control, the return light of the laser light applied to the plate sheet 13 is detected on the optical block 15 side, and the state of the return light is controlled to be appropriate. Such focus control is called optical focus servo control.

[0008]

When such an optical focus servo control is performed, a clamping plate 14 for fixing the plate sheet 13 to the plate cylinder 12 is used.
For this reason, the state of the temporarily detected return light is disturbed, so that there is a problem that the focus servo control cannot be performed (the focus servo control pull-in range is exceeded). That is, the portion where the clamping plate 14 for fixing the end portion of the plate sheet 13 to the plate cylinder 12 is protruded by the thickness thereof, so that the focus control state is disturbed. For this reason, immediately after the irradiated laser beam passes through the place where the clamping plate 14 is located, the focus control state is disturbed, so that the surface of the plate sheet 13 cannot be accurately focused, and accurate plate making cannot be performed.

Therefore, in the vicinity of the edge of the plate sheet 13 stopped by the clamping plate 14, accurate focus control cannot be performed, and the irradiation position of the laser beam passes through the clamping plate 14 to some extent, and the focus control state is stopped. Until is stabilized (after returning to the focus servo control pull-in range), the plate making operation using the laser beam cannot be performed. Normally, it takes several seconds from the state where the focus servo control pull-in range is exceeded to the point where the focus servo control is performed again to return to the focus servo control pull-in range. For this reason, there is an inconvenience that it is difficult to make a plate at the end of the plate sheet 13. In particular, plate cylinder 1
In the case where the speed of plate making can be increased at a high speed by increasing the rotation speed of 2, the area of the end portion where the plate cannot be made becomes large.

Further, even when dust or the like adheres to the surface of the plate sheet 13, there is a problem that the focus control is temporarily disturbed by the projection due to the adhering substance and the plate making state near the adhering substance is deteriorated. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a laser plate making apparatus capable of stably controlling the focus of an irradiated laser beam.

[0012]

According to the present invention, as shown in FIG. 1, for example, a rotating plate cylinder 12, and a laser light source 3 for irradiating a plate sheet 13 wound around the plate cylinder 12 with laser light.
1, a focus adjustment lens 33 for adjusting the focus of the laser light from the laser light source 31, a focus detection unit 38 for detecting a focus state of the laser light from the laser light source 31, and one of the focus adjustment lenses 3
The two electrode plates 51 and 52 attached to the three sides,
A capacitance detecting means 50 for detecting a capacitance generated between the two electrode plates 51 and 52;
And a driving unit 37 for driving the focusing unit into a focused state. In a normal state, according to the detection state of the focus detecting unit 38,
The driving means 37 drives the focus adjustment lens 33 to perform optical servo control for irradiating the laser beam. If the optical servo control cannot be performed, the capacitance detecting means 50
The focus adjusting lens 33 is driven by the driving unit 37 in accordance with the detection state of the above, and the capacitance servo control for irradiating the laser beam is performed.

In this case, the position of the clamping plate 14 for fixing the plate sheet 13 to the plate cylinder is detected by the rotary encoder 20 for detecting the rotational position of the plate cylinder 12.
The capacitance servo control is performed at the detected position of the clamping plate 14.

In this case, one end of a leaf spring 36 is connected to the support member 32 of the focus adjusting lens 33, and the other end of the leaf spring 36 is connected to the optical block. One of the two electrode plates 51 is attached, and the other electrode plate 52 is attached to the optical block side.

Further, in this case, when there is no abnormality in the detection state of the focus detection means 38 during the capacitance servo control, the control is switched to the optical servo control.

[0016]

According to the present invention, when the focus control by the optical servo control is disturbed, the focus control is switched to the capacitance servo control, and the position of the focus adjustment lens is kept constant by keeping the capacitance constant. Is performed, and the laser beam irradiation is performed stably.

Further, in this case, the position of the clamping plate for stopping the plate sheet on the plate cylinder is detected, and switching to the capacitance servo control is performed at the portion where the clamping plate is disposed, so that the clamping plate is disposed. Disturbance of focus control in the set portion can be reliably suppressed.

Further, in this case, the focus adjustment lens is connected to the optical block via a leaf spring, and one of the electrode plates is attached to this leaf spring, so that the electrode plates are efficiently arranged. Capacitance can be detected well.

Further, in this case, when the detection state of the focus detecting means is no longer abnormal while the capacitance servo control is being performed, switching to the optical servo control allows quick and accurate optical servo control. Focus control can be performed.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In FIGS. 1 to 4, the same reference numerals are given to portions corresponding to FIG. 6 described in the conventional example, and the detailed description thereof will be omitted.

FIG. 1 is a diagram showing the configuration of a portion relating to focus control of laser light in the laser plate making apparatus of the present embodiment. In this example, the input terminal 31 of the optical block 31
The semiconductor laser in the optical block 31 outputs a laser beam based on the drive signal obtained in a. The focus of the output laser light is adjusted by an objective lens 33 attached to a lens unit 32, and the laser light is applied to a plate sheet 13 wound around the plate cylinder 12.

A coil 34 is wound around the lens unit 32, and a focus adjustment signal is supplied to the coil 34 from a lens driving circuit 37 described later. A magnet 35 is disposed around the lens unit 32, and the lens unit 32 and the magnet 35 are connected by a leaf spring 36, and the direction of the optical axis of the laser beam (arrow x in FIG. 1). (In the direction indicated by), the lens unit 32 can be moved. The magnet 35
Is fixed to the optical block 31 side.

With this configuration, the focus adjustment signal is supplied from the lens drive circuit 37 to the coil 34, so that the position of the objective lens 33 (position in the x direction)
Is a position corresponding to the current amount of the focus adjustment signal. When the focus adjustment signal is not supplied to the coil 34, the objective lens 33 is fixed at a predetermined position by the action of the leaf spring 36.

Then, in the optical block 31, the return light of the laser light applied to the plate sheet 13 is detected by a plurality of photodetectors. Then, the detection data of the photodetector is supplied to the optical servo circuit 38 to detect the focus state of the laser light.

Then, a voltage signal proportional to the amount of focus shift is obtained from the detected focus state data, and this voltage signal is supplied to the first fixed contact 39a of the changeover switch 39.
To supply. The changeover of the changeover switch 39 is controlled by a central control device 42 described later. The movable contact 39m of the changeover switch 39 is connected to the first fixed contact 39.
When connected to a, this voltage signal is supplied to the lens drive circuit 37. The lens drive circuit 37 changes the amount of current of the focus adjustment signal supplied to the coil 34 according to the level of the supplied voltage signal. In this manner, optical servo control for performing focus adjustment according to the focus state of the laser light to be irradiated is performed.

An electrode plate 51 is attached to a portion of the plate spring 36 connecting the lens unit 32 and the magnet 35, to which the lens unit 32 is attached. Then, an electrode plate 52 is mounted at a position facing the electrode plate 51, and the distance between the two electrode plates 51, 52 is changed by changing the position of the lens unit 32 in the x direction by the focus adjustment described above. The electrode plate 52 is fixed to the optical block 31 together with the magnet 35. In addition, each electrode plate 51,
52 is attached while being insulated from the surroundings.

The capacitance generated between the two electrode plates 51 and 52 is detected by the capacitance servo circuit 50.
The capacitance servo circuit 50 includes two electrode plates 51, 5
A circuit that performs servo control so that the capacitance generated between the two becomes constant, and outputs a voltage signal based on a change in the capacitance. The configuration of the capacitance servo circuit 50 will be described later.

The voltage signal output from the capacitance servo circuit 50 is supplied to the second fixed contact 39b of the changeover switch 39. Therefore, when the movable contact 39m of the changeover switch 39 is connected to the second fixed contact 39b, this voltage signal is supplied to the lens drive circuit 37 and
Capacitive servo control is performed in which control is performed to keep the capacitance generated between the electrode plates 51 and 52 constant (that is, control to keep the position of the lens unit 32 constant).

In this embodiment, a rotary encoder 20 is mounted on the plate cylinder 12 so that the rotary position of the plate cylinder 12 can be detected by the rotary encoder 20. That is, a clamping plate 14 for stopping the plate sheet 13 is attached to the plate cylinder 12, and the position (the angle range of θ ₁ in FIG. 1) where the clamping plate 14 is attached is The fact that the position overlaps with the irradiation position of the laser beam
Is detected by the position detection circuit 41 from the output of When the position detection circuit 41 detects the overlap between the clamping plate 14 and the irradiation position of the laser beam, it supplies a hold command to the central controller 42.

The central control unit 42 is composed of a microcomputer, and switches between the optical servo and the capacitance servo by switching the above-mentioned switch 39. Further, data of the focus detection state in the optical servo circuit 38 is supplied to the central controller 42. Further, the operation of the optical servo circuit 38 and the operation of the capacitance servo circuit 50 are controlled by the central controller 42.

Next, the configuration of the capacitance servo circuit 50 will be described.
This will be described with reference to FIG. This capacitance servo circuit 50
Represents the capacitance generated according to the distance d between the two electrode plates 51 and 52 disposed in the vicinity of the lens unit 32, by the capacitance −
The detected capacitance value is converted by the frequency conversion circuit 53 into a corresponding frequency and output. Therefore, a change in the capacitance value becomes a change in the output frequency. The frequency signal output from the capacitance-frequency conversion circuit 53 is supplied to the phase comparator 54. This phase comparator 54
Then, the phase of the frequency signal supplied from the capacitance-frequency conversion circuit 53 is compared with the phase of the oscillation signal supplied from the voltage controlled oscillator (VCO) 56, and the comparison error signal is supplied to the low-pass filter (LPF) 55. I do. The error signal (voltage signal) DC-converted by the low-pass filter 55 is supplied to the control terminal of the voltage-controlled oscillator 56 and to the output terminal 57 of the capacitance servo circuit 50. Then, the voltage signal obtained at the output terminal 57 is
It is supplied to the changeover switch 39 side.

With the configuration of the capacitance servo circuit 50, the phase comparator 54 and the low-pass filter 55
And the voltage-controlled oscillator 56 constitute a PLL loop, and output a voltage signal corresponding to a change in capacitance.

The other parts are configured in the same manner as the conventional laser plate making apparatus.

Next, the operation related to the switching of the servo control of the laser plate making apparatus thus configured will be described with reference to the flowchart of FIG. First, under the control of the central controller 42, the movable contact 39m of the changeover switch 39
Is connected to the first fixed contact 39a, the output of the optical servo circuit 38 is supplied to the lens driving circuit 37, and the lens unit 32 is controlled by the optical servo control so that the focus state of the laser beam becomes the best. Servo control is performed (step 101).

At this time, the central controller 42 determines whether the focus state detected by the optical servo circuit 38 is abnormal (step 102). Here, when it is determined that the focus state is not abnormal and stable, it is determined whether or not a hold command is supplied from the position detection circuit 41 (step 103). When it is determined that there is no hold command, the process returns to step 101 and the optical servo control based on the output of the optical servo circuit 38 is continued.

When it is determined in step 103 that the hold command has been supplied, the central control unit 42 switches the changeover switch 39 so that the capacitance servo circuit 5
The control is switched to the capacitance servo control using 0 (step 104). Also, when it is determined in step 102 that the focus state is abnormal, the process proceeds to step 104 to switch to the capacitance servo control. While the capacitance servo control is being performed, the capacitance is kept constant (that is, in a state where the position of the lens unit 32 is constant, for example, at a position within the pull-in range of the focus servo control, preferably at the center). Control to be maintained in position).

When the capacitance servo control is performed, it is determined whether or not the hold command is continuously supplied (step 105), and it is determined whether the focus state detected by the optical servo circuit 38 is abnormal. (Step 106). Then, when it is determined in step 105 that the hold command is supplied continuously,
If it is determined in step 6 that the focus state is still abnormal, the process returns to step 104 to continue the capacitance servo control.

If it is determined in step 105 that the hold command has not been supplied, and if it is determined in step 106 that the focus state is not abnormal, the flow returns to step 101 to return to the optical servo circuit based on the output of the optical servo circuit 38. Switch to control. In this case, the time from when the capacitance servo control is switched to the optical servo control to when the focus servo control is normally switched, that is, the pull-in time is determined by the lens unit 3 in step 104.
Since 2 is held at a position within the focus servo control range, it takes only about several milliseconds.

By switching the servo control of the focus of the laser beam in this way, good focus control as a plate making apparatus is performed. That is, in the plate making apparatus of this embodiment, the plate sheet 13 is fixed to the plate cylinder 12 by using the clamping plate 14. The clamping plate 14 projects from the surface of the plate cylinder 12, and the plate making laser When the light irradiation position is at the position of the clamping plate 14 (the angle range of θ ₁ in FIG. 1), the distance from the laser source to the irradiation position is reduced by the thickness of the clamping plate 14. Therefore, if the optical servo control is performed as it is, a large disturbance occurs in the focus detection signal.

Here, in this example, when the irradiation position of the plate-making laser beam reaches the position of the clamping plate 14, a hold command is supplied to the central control unit 42, and the control is switched to the capacitance servo control. Servo control is performed so that the position of the lens unit 32 immediately before switching to the capacitance servo control is maintained. For this reason, when the irradiation position of the plate making laser beam passes the clamping plate 14 and returns to the optical servo control, the focus state detected by the optical servo circuit 38 is The focus state is almost the same as the focus state immediately before the position, and the focus state almost coincides with the surface of the plate sheet 13. Even if the focus state is not accurate, slight shift occurs. To make a flash (for example, what used to take several seconds in the past is now several milliseconds in this example)
Becomes possible.

Accordingly, the plate making by the laser beam can be resumed immediately after passing the clamping plate 14 and the plate sheet stopped by the clamping plate 14 even if the rotation speed of the plate cylinder 12 is increased. The plate making can be performed accurately from the end of the plate 13, the plate making speed can be increased, and the plate can also be made accurately at the end of the plate sheet 13.

In this embodiment, even when dust or the like adheres to the surface of the plate sheet 13, disturbance of the focus of the laser beam can be minimized. That is, as shown in FIG. 1, for example, when dust 13a adheres to the surface of the plate sheet 13, the distance from the laser source to the irradiation position is shortened by the amount of the protrusion due to the dust 13a. When the servo control is performed, a large disturbance occurs in the focus detection signal, and it takes time until the focus control state is stabilized after passing the portion where the dust 13a adheres, and a plate making defect portion having a large area occurs. In contrast,
In the case of this example, if a large disturbance occurs in the focus detection signal, the focus servo signal is switched to the capacitance servo control for maintaining the position of the lens unit 32 immediately before, so that the focus detection signal becomes stable after passing the portion where the dust 13a adheres. Then, when switching to the optical servo control, the focus state becomes almost the same as the focus state immediately before the position where the dust 13a is attached, and it is possible to focus quickly.

FIG. 4 shows an example of a control signal supplied from the central controller 42 of the present embodiment to the changeover switch 39. In this case, when the control signal is a low level signal "L", the movable contact 39m When the optical servo control is being performed by connecting to the first fixed contact 39a, when the high level signal is “H”, the movable contact 39m is connected to the second fixed contact 39b to perform electrostatic control. This shows when the capacitive servo control is being performed.

[0044] As shown in FIG. 4, the installation location of the clamping plate 14 each time the laser light passes once rotation 1, the control signal for a predetermined time period t ₁ is the high level, the capacitance servo switching with switched, when there is adhered portion of the dust 13a is time t ₂ only control signal corresponding to the size of the deposit at that portion becomes a high level, switches the capacitance servo.

Note that, in the above-described embodiment, the two
Although the servo control is performed based on a change in capacitance caused by a change in the interval between the electrode plates 51 and 52, the servo control may be performed by detecting a change in position using another method. For example, as shown in FIG. 5, an electrode plate 58 attached to the lens unit 32 and an electrode plate 59 attached to the magnet 36 are arranged facing each other along the direction in which the lens unit 32 moves. And both electrode plates 5
The capacitance generated between 8, 59 is transferred to the capacitance servo circuit 50.
Alternatively, the detection may be performed. In this case, each electrode plate 5
8, 59 are mounted in a state insulated from the surroundings. By doing so, when the position of the lens unit 32 changes,
The area where the electrode plate 58 and the electrode plate 59 directly oppose changes, the capacitance changes, and the same control as in the above-described embodiment becomes possible.

Further, the position of the lens unit may be detected by a method other than the change of the capacitance.

Further, in the above-described embodiment, the present invention is applied to a laser plate making apparatus. However, the present invention can be applied to a focus servo control of another laser beam. For example, the present invention can be applied to control for recording and reproducing data on an optical disk or a magneto-optical disk by irradiating a laser beam. By applying the present invention to recording and reproduction of a disk, good focus control can be performed even when the surface of the disk is damaged.

Further, it goes without saying that the present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0049]

According to the present invention, when the focus control by the optical servo control is disturbed, the control is switched to the capacitance servo control, and the position of the focus adjustment lens is kept constant by keeping the capacitance constant. Focus control is performed, and laser light irradiation is stably performed.

Further, in this case, the position of the clamping plate for stopping the plate sheet on the plate cylinder is detected, and by switching to the capacitance servo control at the portion where the clamping plate is disposed, the clamping plate is disposed. This has the effect that disturbance of focus control in the set portion can be reliably suppressed.

Further, in this case, the focus adjustment lens is connected to the optical block via a leaf spring, and one of the electrode plates is attached to the leaf spring, so that the electrode plates are efficiently arranged. This has the effect that the capacitance can be detected well.

Further, in this case, when the detection state of the focus detecting means is no longer abnormal when the capacitance servo control is being performed, the optical servo control is switched to quickly and accurately by the optical servo control. This has the effect of enabling focus control.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a configuration diagram showing a capacitance servo circuit according to one embodiment of the present invention.

FIG. 3 is a flowchart showing a servo switching operation according to one embodiment of the present invention.

FIG. 4 is a timing chart showing a switching state according to an embodiment of the present invention.

FIG. 5 is a configuration diagram showing another embodiment of the present invention.

FIG. 6 is a configuration diagram showing an example of a conventional plate making apparatus.

[Explanation of symbols]

 12 plate cylinder 13 plate sheet 14 clamping plate 20 rotary encoder 31 optical block 32 lens unit 33 objective lens 34 coil 36 leaf spring 37 lens drive circuit 38 optical servo circuit 39 changeover switch 41 position detection circuit 42 central control device 50 electrostatic Capacitance servo circuit 51, 52 Electrode plate

──────────────────────────────────────────────────の Continued on the front page (58) Fields surveyed (Int. Cl. ⁶ , DB name) B41C 1/00-1/18 G02B 7/11 G02B 27/00 B23K 26/00-26/18

Claims (4)

(57) [Claims] 1. A rotating plate cylinder, a laser light source for irradiating a laser beam to a plate sheet wound around the plate cylinder, a focus adjusting lens for adjusting a focus of the laser light from the laser light source, Focus detecting means for detecting a focus state of laser light from a laser light source; two electrode plates attached to the focus adjustment lens side; and a capacitance generated between the two electrode plates. An electrostatic capacitance detection unit; and a driving unit that drives the focus adjustment lens to a state where the focus adjustment lens is focused. Normally, the drive adjustment unit uses the focus adjustment lens according to a detection state of the focus detection unit. Is driven to irradiate laser light, and when the optical servo control cannot be performed, the drive is controlled according to the detection state of the capacitance detecting means. By driving the focus adjusting lens in section, a laser plate making apparatus being characterized in that to perform the capacitance servo control for irradiating a laser beam. 2. A position of a clamping plate for holding a plate sheet on a plate cylinder is detected by a rotary encoder for detecting a rotational position of the plate cylinder. Capacitance servo control is performed based on the detected position of the clamping plate. 2. The method according to claim 1, wherein the step is performed.
The laser plate making apparatus described in the above. 3. One end of a leaf spring is connected to the support member of the focus adjusting lens, the other end of the leaf spring is connected to the optical block side, and one end of the leaf spring is connected to one end of the leaf spring. 2. A laser plate making apparatus according to claim 1, wherein one of said plates is attached, and said other electrode plate is attached to said optical block side. 4. The laser according to claim 1, wherein, when the capacitance servo control is performed, when there is no abnormality in the detection state of the focus detection means, the laser is switched to the optical servo control. Plate making equipment.