JP2003334987A - System and method for exposing image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system and a method for exposing an image in which phase lag can be improved without enhancing response of feedback control. <P>SOLUTION: In an image recorder 10, displacement of a scanning line is measured on the surface of a recording medium P just before exposure on the downstream side in the subscanning direction M and the movement target signal of a lens unit is generated from displacement data on that scanning line by waveform operation. A light beam is then focused by the lens unit while constantly focusing on the surface of the recording medium P wound around the outer surface of a drum 30 rotating at a constant speed by means of an auto-focus mechanism provided in an exposure head 40, and the recording medium P is scanned in the subscanning direction M parallel with the axial direction of the drum 30 by means of the exposure head 40 while being scanned in the rotational direction r thus exposing a specified image two-dimensionally on the surface of the recording medium P in the recording direction R with the light beam. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image exposure apparatus and an image exposure method used in printing and plate manufacturing,
In particular, the present invention relates to an image exposure apparatus and an image exposure method for performing optical alignment using an autofocus mechanism and recording an image on a recording medium such as a PS plate (Presensitized Plate) using a light beam.

[0002]

2. Description of the Related Art Currently, an image recording apparatus by scanning exposure using a light beam or the like as recording light is used in a printing plate making apparatus, a copying apparatus and various printers. Of these, an outer drum in which a drum that holds a recording medium such as a PS plate and holds the recording medium on its outer surface and an exposure optical system that makes a light beam modulated according to a recorded image enter and form an image at a predetermined exposure position are used. There is a stencil plate exposure device. In such an outer drum type plate exposure apparatus, a drum holding a recording medium is rotated about its center line as a rotation axis, and while the recording medium is mainly scanned in the rotation direction by an optical system, the optical system is rotated in the rotation axis direction. By moving the recording medium to the position (1) and sub-scanning the recording medium, the recording medium is helically scanned by the light beam, and an image is two-dimensionally recorded on the recording medium.
In such an outer drum type plate exposure apparatus, considering the cost and the like, it is practically impossible to make the drum into a complete cylindrical shape, and the peripheral surface of the drum always has a gentle undulation. There are irregularities. As a result, the surface of the recording medium held on the drum fluctuates along the unevenness. That is, the exposed surface of the recording medium surface changes.

Further, when foreign matter such as dust and dirt intervenes between the recording medium and the drum, the foreign matter causes the recording medium to be lifted from the back surface, and the foreign matter is caught on the front surface of the recording medium. Protrusions are formed according to the size of the foreign matter, and irregularities are formed on the exposed surface. Further, depending on the method of holding the recording medium, unevenness may occur on the surface of the recording medium. Further, the centrifugal force generated by the rotation of the drum causes distortion in the drum, which also causes the recording medium to have irregularities.

FIG. 11 is a graph showing the intensity distribution of the light beam. In FIG. 11, the horizontal axis represents the surface direction and the vertical axis represents the light intensity, showing the difference in the intensity distribution of the light beam due to the difference in the distance between the recording surface and the lens. Note that distribution a shown in FIG. 11 shows the case where the distance between the drum and the lens is the focal length, and distributions b and c show the case where the depth is out of the focal depth.

When the exposed surface of the recording medium has unevenness and the unevenness is larger than the depth of focus of the light beam, the following problems occur. As shown in distributions b and c of FIG. 11, when the light beam deviates from the depth of focus, the diameter of the light beam incident on the recording medium becomes thicker than that of the distribution a, and the beam spot of the light beam incident on the exposure surface becomes larger. The light amount distribution (exposure energy distribution) is in a broad state in which the maximum light amount is low and the half width is wide. As a result, when forming a fine line or the like extending in the sub-scanning direction on the recording medium, sufficient exposure energy cannot be applied by recording in the main scanning direction, and the line becomes thinner than the desired fine line. Defect occurs.
As a result, the area ratio of halftone dots deviates from the predetermined value, and the density of the printed matter created based on this plate deviates from the predetermined density.

Therefore, conventionally, the distance between the recording medium surface (plate surface) and the exposure optical system and the position of the focus lens for focusing the light beam are measured by a sensor, and the focus lens is moved by an actuator to change the focal length. A device having an autofocus function for adjusting has been proposed.

FIG. 12 is a block diagram showing a conventional autofocus control device. As shown in FIG. 12, the conventional auto-focus control device 200 includes a displacement calculation / waveform shaping circuit 202, a CPU 204 connected to the displacement calculation / waveform shaping circuit 202, and an output of the displacement calculation / waveform shaping circuit 202. And a feedback control unit 210 to be input. In this autofocus control device 200, a voice coil motor (hereinafter, also referred to as VCM) is used as an actuator.

The displacement calculation and waveform shaping circuit 202 fixes the plate size and the plate calculated from the drum displacement data indicating the displacement of the distance between the recording medium surface and the exposure optical system, and the output signal of the encoder provided on the drum. The VCM (voice coil motor) driving target signal is generated based on the chuck position data. CPU20
Reference numeral 4 is for performing displacement calculation and calculation of the waveform shaping circuit 202. The feedback control unit 210 has an amplifier 212 that amplifies a deviation signal, which will be described later, and a VCM system 214 to which the signal from the amplifier 212 is input.
The amplifier 212 receives a deviation signal that is the difference between the VCM driving target signal output from the displacement calculation and waveform shaping circuit 202 and the output signal of the VCM system 214,
This deviation signal is amplified. VCM system 2
Reference numeral 14 is for calculating the movement amount of the VCM used as the actuator based on the deviation signal.

As described above, in the conventional feedback control device, the VCM driving target signal is generated based on the drum displacement data and the output signal of the drum encoder. Based on this VCM driving target signal, feedback control is performed by an actuator that drives the focus lens and a sensor that detects the position of the focus lens.

[0010]

However, in general, the high speed response is expressed by the amplitude (gain) and the phase, and the phase starts to be delayed in the region of the low response frequency as compared with the decrease of the amplitude. In the autofocus control device, the phase delay increases the tracking error, and therefore needs to be minimized. In conventional feedback control, response performance itself must be improved in order to reduce the phase delay. For example, when performing an autofocus control of several hundreds Hz, a response (crossover frequency) about 5 times that is required, and the response frequency is 500 Hz to 1 kHz.

As described above, in the conventional feedback control device, in order to realize stable feedback control, the resonance point of the lens support member or the like needs to be equal to or higher than the crossing frequency. Therefore, a lens guide mechanism having extremely high rigidity is required, which causes a problem that the mass of the lens guide mechanism increases. Further, due to side effects such as an increase in the mass of the lens guide mechanism, an actuator having a higher thrust is required, which causes a problem of cost increase.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image exposure apparatus and an image exposure method capable of improving the phase delay without increasing the responsiveness of feedback control.

[0013]

In order to achieve the above-mentioned object, a first aspect of the present invention is directed to a method of exposing a surface of a recording medium wound around an outer surface of a drum rotating at a constant speed to a light beam by an exposure unit. Is an image exposure apparatus that performs main scanning in the drum rotation direction, performs sub-scanning while moving the exposure unit along the axial direction of the drum, and two-dimensionally exposes an image. A pair of parallel members that are connected to the housing via a first elastic member and that are swingable with respect to the drum while maintaining a parallel state. A swinging member connected to the parallel member via a second elastic member, a lens unit mounted on the swinging member for focusing a light beam on the surface of the recording medium, and the swinging unit. Member to the drum And an image exposure apparatus characterized by comprising an actuator for near or away from, the. In this case, the first and second elastic members are leaf springs, for example.

In the present invention, further, the displacement of the recording medium wound around the rotating drum is measured at the downstream side of the image forming position of the light beam by the exposure unit in the sub-scanning direction. It is preferable to have displacement measuring means and lens position measuring means for measuring the position of the lens unit.

According to a second aspect of the present invention, the surface of a recording medium wound around the outer surface of a drum rotating at a constant speed is mainly scanned in the drum rotating direction by a light beam by an exposure unit and the exposure is performed. An image exposure method in which a unit is sub-scanned while moving along the axial direction of the drum to two-dimensionally expose an image, which is located downstream of the imaging position of the light beam in the sub-scanning direction. A step of measuring the displacement of the recording medium immediately before the exposure, and a movement amount target signal for moving the lens unit that forms the light beam on the surface of the recording medium by waveform calculation from the displacement data of the recording medium immediately before the exposure. And a step of exposing the image by moving the lens unit based on the movement amount target signal. In the Rukoto.

Further, according to a third aspect of the present invention, the surface of the recording medium wound around the outer surface of the drum rotating at a constant speed is mainly scanned in the drum rotating direction by a light beam by an exposure unit and the exposure is performed. An image exposure method in which a unit is sub-scanned while moving along the axial direction of the drum to two-dimensionally expose an image, which is located downstream of the imaging position of the light beam in the sub-scanning direction. A step of measuring the displacement of the recording medium immediately before exposure, and a first movement amount target signal for feedforward control and a second movement for feedback control by waveform calculation from displacement data of the recording medium immediately before exposure. A step of generating an amount target signal, and using the displacement data of the recording medium at the time of exposure as a feedback signal, the feedback signal and the first movement amount target signal. And a step of generating a focusing target value signal of the lens unit for forming the light beam on the surface of the recording medium based on the second movement amount target signal; and moving the lens unit based on the focusing target value signal. And a step of exposing the image to light, thereby providing an image exposure method.

In this case, the waveform calculation is a calculation for removing high frequency noise of the displacement data of the recording medium, a calculation for removing the data of the fixing means for fixing the recording medium to the outer surface of the drum, and the fixing means. And a calculation for replacing the data of the drum portion where the recording medium does not exist with the data of the leading end portion of the recording medium, and a calculation for advancing the phase of the displacement data.

Further, the waveform calculation is preferably calculated by digital calculation. Further, the waveform calculation is
It is preferably calculated by a digital signal processor.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An image recording apparatus according to the present invention will be described below in detail with reference to the preferred embodiments shown in the accompanying drawings. FIG. 1 is a schematic perspective view showing an image recording apparatus (outer drum type printing plate exposing apparatus) according to an embodiment of the present invention, and FIG. 2 is a side view of the image recording apparatus of the present embodiment. In the image recording apparatus shown in FIG. 1, the recording medium (P
Although an S plate) plate feeding / discharging mechanism, a punching mechanism, a positioning mechanism, and the like are required, they are not shown. Also,
In FIG. 1, illustration of a drum displacement measuring sensor 70 and a mounting table 62 described later is omitted.

The image recording apparatus 10 of the present embodiment is an outer drum type (cylindrical outer surface scanning type) plate exposure apparatus, and is a recording medium P wound and fixed on the outer surface of a drum 30 rotating at a constant speed. The light beam is imaged by the lens unit while always focusing on the surface of the drum 3 by the autofocus mechanism provided in the exposure head 40.
The exposure head 40 is scanned in the rotation direction r (main scanning direction) of 0 while the exposure head 40 is substantially parallel to the axial direction of the drum 30 in the sub scanning direction M.
And a predetermined image is two-dimensionally exposed (recorded) on the surface of the recording medium P in the recording direction R with a light beam.
In the image recording apparatus 10, the displacement of the surface of the recording medium P on the scan line on the downstream side in the sub-scanning direction M immediately before the exposure of the scan line exposed in the main scanning direction of the recording medium P is measured, and the displacement on the scan line is measured. The displacement amount target signal of the lens unit is generated by waveform calculation from the displacement data of
Control is performed so that the distance between the lens unit and the drum 30 is always the focal length.

In order to realize the exposure method of this embodiment,
It is necessary that the displacements of the scan line immediately before exposure and the exposure scan line are substantially the same. The exposure line width in this embodiment is about 10 to 20 although it varies depending on the type of the light source.
Since it is about 00 μm, and the variation of the shape in the sub-scanning direction is gentle such as undulation, it can be used without any problem, for example, to generate a feedforward control signal.

In the present invention, the recording medium P that can be used is not particularly limited, and various photosensitive materials can be used. Among them, a binary photosensitive material is preferable, in which only the portion where the exposure energy exceeds the threshold value is recorded at a predetermined value and the other portions are not recorded, in that the effects of the present invention can be suitably exhibited. Above all, a so-called thermal type photosensitive material (heat mode photosensitive material) which converts a light beam into heat energy and forms an image by this heat energy is particularly preferable. Image recording apparatus 10 of the present embodiment
Is for recording an image on this photosensitive material (hereinafter referred to as a thermal photosensitive material).

The image recording apparatus 10 basically comprises a base 12
The guide rail 14, the main scanning motor 22, the sub-scanning motor 28, the drum 30, the exposure head 40 (exposure unit), and the controller 100. The base 12 is provided with a guide rail 14 on which the sub-scanning motor 28, the drum 30, and the exposure head 40 are placed. The drum 30 has an outer peripheral surface around which a recording medium P such as a PS plate is wound, and a front end chuck 34 and a rear end chuck 36 for fixing and holding the recording medium P are provided on the outer peripheral surface of the drum 30. (See Figure 2). The drum 30 is rotatably supported by a pair of support members 16 provided on the base 12 via bearings (not shown) on both sides of a rotation shaft (not shown). A rotary encoder 26 is provided on one end of the rotary shaft of the drum 30. The rotary encoder 26 detects the rotation angle of the drum 30, and the positions of the leading end chuck 34, the trailing end chuck 36, and the recording medium P are specified by this.

The leading end chuck 34 and the trailing end chuck 36 for fixing and holding the recording medium P on the drum 30 are not particularly limited, and the leading end chuck 34 and the trailing end chuck 36 use a magnet and a means. Various known means such as means for fixing the fixing member with a bolt can be used.

The main scanning motor 22 is a rotation driving means for rotating the drum 30, and has a rotation shaft (not shown),
A pulley 24 is provided at its end. Drum 30
Has a pulley 18 at the end of the other rotating shaft. The pulley 18 and the pulley 24 are connected to each other via a winding transmission means such as a belt 20. The rotation of the main scanning motor 22 is transmitted to the drum 30 via the rotation shaft of the main scanning motor 22, the pulley 24, the belt 20, the pulley 18, and the rotation shaft of the drum 30, and the drum 30 rotates in the rotation direction r. The rotation driving means and the winding transmission means are not particularly limited to those described above, and known rotation driving means and winding transmission means such as a chain can be used. Further, the main scanning motor 22 and the drum 30 are not limited to those in which power is transmitted by the winding transmission means, and may be transmission means such as gears.

The guide rail 14 guides the exposure head 40 in the axial direction of the drum 30 (sub-scanning direction M). The guide rails 14 are a pair of rails provided on the edge of the base 12, and extend along the axial direction of the drum 30. A ball screw 15 is provided between the guide rails 14 along the axial direction.

The sub-scanning motor 28 is a driving means for moving the exposure head 40 in the sub-scanning direction M, and is connected to one end of the ball screw 15. This sub-scanning motor 2
Reference numeral 8 is preferably a pulse motor because it is necessary to control the amount of movement of the exposure head 40 in the sub-scanning direction M. The sub-scanning motor 28 may be connected to the ball screw 15 via the above-mentioned transmission means, for example. In this way, the exposure head 40 is driven by the sub-scanning motor 28.
It is moved in the sub-scanning direction M along the guide rail 14.

As shown in FIG. 2, the exposure head 40 has an L
The light emitted from the light source 90 such as an ED is collimated by the collimator lens 92, and then the collimated light is imaged on the surface of the recording medium P by the lens unit 60 described later. The exposure head 40 is provided with a lower table 40a, and a lower surface of the lower table 40a is provided with a guide member 40b extending in the axial direction of the drum 30 at a position aligned with the guide rail 14. Guide member 40
A guide 40c that is screwed with the ball screw 15 is provided between b and 40b. The guide member 40b is
The guide rail 1 is not particularly limited.
4 and those which can be guided in a rolling state or a sliding state. Further, the exposure head 40 includes a lens unit 60.
It has a driving means (actuator) 50 for driving, a drum displacement measuring sensor 70, and a lens displacement sensor 80. The detailed structure and operation of the exposure head 40 will be described later.

Further, in this embodiment, one light source 9
The invention is not limited to image recording by one light beam emitted by 0, and a plurality of light sources such as an LED array or a plurality of light sources in which optical fibers and LDs are combined are arranged as a light source. It can be suitably used for image recording using so-called multi-beam exposure, in which recording is performed simultaneously.

As shown in FIG. 1, the control unit 100 includes a main scanning motor driver 102 and a sub scanning motor driver 10.
4, the mechanical control circuit 106, the transport unit 108,
An AF system circuit 110, a laser driver 112,
It has a synchronous circuit and exposure data generation circuit 114, a laser control circuit 116, and a CPU 118.

The main-scanning motor driver 102 rotates the main-scanning motor 22 at a predetermined rotation speed, which causes the drum 30 to rotate at a predetermined rotation speed. The sub-scanning motor driver 104 rotates the sub-scanning motor 28 at a predetermined number of rotations, and the rotational movement of the sub-scanning motor 28 is converted into a linear movement by the ball screw 15 so that the exposure head 40 moves in the sub-scanning direction M. Moving. Sub-scanning motor 28
Is a stepping motor, the rotation speed and the rotation amount are controlled to control the exposure head 40 in the sub-scanning direction M.
Position and exposure head 4 in the sub-scanning direction M
The scanning speed of 0 can also be adjusted.

The mechanical control circuit 106 is connected to the main scanning motor driver 102 and the sub-scanning motor driver 104, and gives a signal for driving the main scanning motor 22 and the sub-scanning motor 28. For example, the operations of the main scanning motor 22 and the sub scanning motor 28 are synchronized.

The transport unit 108 is a plate feeding / discharging mechanism for the recording medium P, and supplies the recording medium P to the drum 30 at the time of image recording and also discharges the recording medium P from the drum 30 after the image recording is completed. is there. Recording medium P
The mechanical control circuit 106 supplies and discharges the drum to and from the drum 30.
Controlled by.

The AF system circuit 110 includes the exposure head 4
0 (lens unit 60) and recording medium P (drum 30)
This is for keeping the distance between and always constant, and the details will be described later. The laser driver 112 is for emitting a light beam necessary for exposure from the light source 90, and turns on and off the light source 90 based on the output of the laser control circuit 116 described later.

Synchronous circuit and exposure data generation circuit 11
Reference numeral 4 is connected to the rotary encoder 26 and measures the positions of the front end chuck 34 and the rear end chuck 36, that is, the position of the recording medium P on the drum 30. The laser control circuit 116 is connected to the laser driver 112 and the synchronization system circuit and exposure data generation circuit 114, and the laser driver 112 is provided with a light source based on the result detected by the synchronization system circuit and exposure data generation circuit 114. A control signal for controlling on / off of the injection of 90 is output. Further, for example, when an LED is used as the light source 90, a change in wavelength due to a change in temperature is compensated. Furthermore, when a plurality of lights from a plurality of light sources are made to enter one lens unit 60, the light sources not required for exposure are turned off. CPU
Reference numeral 118 denotes the mechanical control circuit 106 and the AF system circuit 11
0, the laser control circuit 116, and the synchronization system circuit and the exposure data generation circuit 114, and is responsible for the calculation in these circuits.

FIG. 3 is a perspective view showing the exposure head of the image recording apparatus of this embodiment, and FIG. 4 is a side view seen from the direction A in FIG. As shown in FIG. 3, the exposure head 40 includes a substrate 42 and side plates 44 provided upright on both sides of the substrate 42.
And a frame body 41 having an opening in two directions, which is composed of an upper plate 46 connected to an upper portion of a side plate 44, the frame body 41 being opposed to the substrate 42. 3 and 4, the side plate 44 on one side (direction A side) is not shown. The frame 41 is arranged such that one opening 41a thereof faces the drum 30 (see FIG. 4). The drum 30 of the upper plate 46
The rocking plates 58, 59 (a pair of parallel members) are provided on the end portion on the side facing the and the end portion on the opposite side via the first elastic pieces 56a, 56a (first elastic member), respectively. It is provided on the plate 46. Both ends of the first elastic piece 56a are fixed to the upper plate 46 and the swing plates 58, 5 by the stopper plates 54a, respectively.
It is fixed at 9. Thereby, the swing plates 58, 59
Can approach and separate from the drum 30.

The swing plate 58 on the side facing the drum 30 has an opening 58a at a position aligned with the lens unit 60.
Is provided. Furthermore, on the swing plate 59 on the opposite side,
An opening 59a is provided at a position aligned with the lens unit 60, and the light source 90 (see FIG. 2) is provided through the opening 59a.
The collimated lens 92 (see FIG. 2) collimates the light from the collimated lens 92 (see FIG. 2) and enters the collimated light.

At the lower ends of the rocking plates 58 and 59, a rocking member 51 is provided via a second elastic piece 56b (second elastic member).
Are connected. The second elastic piece 56b serves as a stopper plate 5.
4b, both ends thereof are fixed to the swing plates 58 and 59 and the swing member 51. At this time, it is preferable that the first and second elastic pieces 56a and 56b have a strip shape.
In this way, the swinging member 51, the swinging plates 58 and 59, the first elastic piece 56a, and the second elastic piece 56b form a parallel link. As a result, the swing plates 58 and 59 can approach and separate from the drum 30 together with the swing member 51 in a state where the swing plates 58 and 59 remain parallel to each other. The first
As the elastic piece 56a and the second elastic piece 56b, a leaf spring can be used, and as the leaf spring, for example, a thin plate made of stainless steel having a thickness of 50 μm can be used.

The rocking member 51 has bent portions 51a bent horizontally in the lower four corners, and the rocking member 51 is formed.
An upper plate member 51b is provided on the upper end surface of the. A coil portion 52 is provided on the lower surface of the end of each bent portion 51a. A guide portion 48 is provided on the upper surface of the substrate 42. This guide portion 48 is a base member 48a.
A side member 48b provided on the base member 48a at a matching position between the bent portions 51a, and the side member 4b.
8b and a regulating member 48c provided on the upper surface of 8b. The magnet 4 is placed at a position aligned with the coil portion 52 of the base member 48a.
9a is provided. Coil portion 52 of the regulating member 48c
The magnet 49b is provided at a position aligned with. A coil is provided inside the coil unit 52, and a current is applied to the coil from a current supply unit (not shown).

As shown in FIGS. 3 and 4, the voice coil motor 50 (actuator) is constituted by the magnet 49a provided on the base member 48a, the coil portion 52, and the magnet 49b provided on the regulating member 48c. By applying a current to the coil of the coil portion 52, the swing member 51 approaches or separates from the drum 30. That is, as shown in FIG. 4, the distance H between the lens unit 60 and the drum 30 changes. The moving direction of the swinging member 51 is
It can be controlled by changing the direction of the current applied to the coil portion 52. In this case, the lens unit 60
Even if is moved, the oscillating plates 58, 5 are arranged so that the focus position (image forming position) in the vertical direction with respect to the substrate 42 does not change.
The length of 9 and the movement amount of the swinging member 51 are set.

Further, the movement amount of the swinging member 51 with respect to the drum 30 is regulated by the contact between the regulating member 48c and the bent portion 51a. The actuator is not limited to the voice coil motor, and may be an actuator using a piezoelectric element, for example. The lens unit 60 is arranged on the upper plate member 51b of the swinging member 51 so that the optical axis passes through the center of the drum 30, and the lens unit 60 partially projects from the opening 58a. This lens unit 60 is shown in FIG.
As shown in, the contact surface of the upper plate member 51b with the lens unit 60 is regulated by the V-shaped fastening member 64 and is fixed by the band 66. The lens unit 60 has a lens barrel and one lens or a combined lens in which a plurality of lenses are combined, and narrows the incident light so that the incident light has a predetermined spot diameter at the focal position.

The drum displacement measuring sensor 70 is housed inside a housing 68 mounted on a mounting table 62 provided on the upper surface 46a of the upper plate 46. As will be described later, the drum displacement measuring sensor 70 uses a type of triangulation method, and emits measurement light such as a laser beam onto the recording medium P and measures the reflected light to expose the exposure head 40. The distance from the recording medium P is measured.
The housing 68 is provided on the surface facing the drum 30 with an opening 68a through which the emitted light E ₁ (measurement light) described later is emitted and an opening 68b through which the reflected light E ₂ is incident. Further, the mounting table 62 includes a drum displacement measuring sensor 70.
The exit light E _{1 of the} light is inclined so as to pass through the center of the drum 30.

FIG. 5A is a schematic diagram showing the exposure position of the lens and the measurement position of the drum displacement measuring sensor.
(B) is a schematic diagram which shows the structure of a drum displacement measurement sensor. The drum displacement measurement sensor 70 measures the distance between the exposure head 40 and the recording medium P by, for example, a triangulation method, and the measurement position D of the lens displacement measurement sensor 70 is measured.
Are set on the downstream side of the exposure position F of the lens unit 60 in the sub scanning direction M.

As shown in FIG. 5A, it is sufficient that the measurement position D is provided on the downstream side of the exposure position F, and the exposure position F of the exposure head 40 and the measurement position D of the drum displacement measuring sensor 70. In the present invention, the interval δ of is preferably about twice the scanning width of one line by the lens unit 60. Spot diameter is 10 μm when using one light source
In the case of multi-beam exposure, if the number of channels is 20 to 200, the scanning width of one line is 200 μm to 2
It becomes 000 μm (2 mm). Therefore, the distance δ is 5m
It is preferably m or less.

As shown in FIG. 5B, the drum displacement measuring sensor 70 includes an LED 72 (light source), an objective lens 74 for focusing the emitted light E _{1 of the} LED 72 on the recording medium P, and
Reflected light E ₂ from the recording medium P is transmitted to a PSD (Positi
on-sensitivity detector) 78, and an PSD 78 that specifies the position of the reflected light E ₂ . In the PSD 78, photodiodes are continuously arranged in the longitudinal direction, and the balance of the output voltage at both ends changes depending on the light receiving position. In the drum displacement measuring sensor 70, the light E ₁ emitted from the LED 72 is reflected on the surface of the drum 30, and the reflected light E ₂ is focused by the PSD 78. At this time, the balance of the output voltage from the PSD 78 differs depending on the light receiving position of the PSD 78. With this change, the distance between the drum 30 and the exposure head 40 can be measured. In addition, LED7 as a light source
2 is used, that is, by using light having a low coherence, interference of scattered light caused by unevenness of the surface of the PS plate is suppressed, so that the reflected light E
It is preferable because the noise component contained in ₂ is reduced and the measurement accuracy is improved.

In FIG. 4, a lens displacement measuring sensor 80
Is for measuring the amount of movement of the lens unit 60. The lens displacement measuring sensor 80 includes, for example, a reflecting plate 82 provided on the upper part of the lens unit 60 and a measuring section 84 having a light source and a light receiving element and fixed to the upper plate 46 by a fixing member 86. Is mentioned.
The lens displacement measuring sensor 80 may have the same structure as the drum displacement measuring sensor 70, and thus detailed description thereof will be omitted.

FIG. 6 is a block diagram showing the autofocus system of the image recording apparatus of this embodiment. As shown in FIG. 6, the autofocus system 130 in the image recording apparatus of the present embodiment is basically the AF system circuit 1
10, a drum encoder 26, and a synchronous circuit 120 connected to the drum encoder 26. The synchronization system circuit 120 is a part of the synchronization system circuit and the exposure data generation circuit 114, and is connected to the CPU 118.
The synchronization system circuit 120 calculates the position and size of the leading end chuck 34, the trailing end chuck 36 and the recording medium P using the CPU 118 based on the signal from the drum encoder 26.

The AF system circuit 110 includes a drum displacement measuring sensor 70 and a drum displacement measuring sensor drive circuit 13.
2, a lens displacement measurement sensor 80, a lens displacement measurement sensor drive circuit 134, and a lens displacement calculation circuit 136,
Displacement calculation and waveform shaping circuit 138 and AF control circuit 1
50 and a VCM drive circuit 160.

The drum displacement measuring sensor drive circuit 132 is
It is connected to the drum displacement measuring sensor 70, drives the LED 72 of the drum displacement measuring sensor 70 to emit the emitted light E _1, and PSD by the reflected light E ₂ of the recording medium P.
The output voltage of 78 is measured. As a result, the surface shape (drum displacement information (before calculation)) of the recording medium P in the main scanning direction is obtained.

The lens displacement measuring sensor drive circuit 134
It is connected to the lens displacement measuring sensor 80 and drives the LED of the lens displacement measuring sensor 80 to emit emitted light and measures the PSD output voltage due to the reflected light of the reflector 82. Thereby, lens displacement information (before calculation) is obtained. The lens displacement calculation circuit 136 is connected to the lens displacement sensor drive circuit 134, and has a PS
The displacement of the lens is calculated based on the output voltage of D. Thereby, the lens position information is obtained based on the lens displacement information.

The displacement calculation / waveform shaping circuit 138 generates a feedforward control signal and a VCM driving target signal, and outputs these signals to the AF control circuit 150. The synchronous system circuit 120 and the drum displacement measurement are performed. It is connected to the sensor drive circuit 132 and the CPU 118, and inputs drum position information and drum displacement information (before calculation). Thereby, the surface shape of the drum 30 in the scanning line before exposure is measured, and the drum 3
The state at each position of 0 is grasped. The displacement calculation and waveform shaping circuit 138 has a memory (not shown) in which drum position information and drum displacement information (before calculation) are stored.

Next, the displacement calculation and waveform shaping circuit 138.
A method of generating the feedforward control signal and the VCM driving target signal by the method will be described. FIG. 7 is a graph showing a method of generating a feedforward control signal and a VCM driving target signal by the displacement calculation and waveform shaping circuit 138 in the order of steps. (A) shows displacement on the vertical axis and time on the horizontal axis. Shows the drum displacement data for one revolution of the cylindrical drum, (b) shows the output on the vertical axis, shows the VCM driving target signal on the horizontal axis, and (c) shows the output on the vertical axis. 3 is a graph showing a feedforward control signal with time on the horizontal axis. In the drum displacement data shown in FIG. 7A, the output C ₁ corresponds to the position of the front end chuck 34, the output C ₂ corresponds to the position of the rear end chuck 36, and the recording medium P corresponds to the area A. Corresponds to. Figure 7
In (a), the portion other than the area A is the tip chuck 3
4, the rear end chuck 36 and the drum 30 are shown.

First, as shown in FIG. 7B, the outputs C ₁ and C ₂ of the leading end chuck 34 and the trailing end chuck 36 are deleted, the leading end data in the area A is extended, and an extended portion F ₁ is generated. To do. Also on the rear end side, interpolation is performed so as to be the same as the output at the front end, and the rear end portion F ₂ is generated. That is, the data of the area where the recording medium P does not exist is recorded on the recording medium P.
Of the above data, for example, is replaced with the data of the tip portion.
As a result, the operation of the VCM 50 in the area other than the recording medium P (the area where the recording medium P does not exist) is reduced, and the abrupt operation at the start of recording is suppressed, and stable recording can be performed. Next, the high frequency noises S ₁ and S ₂ are removed. As a result, abrupt movement of the lens unit 60 can be suppressed, and instability of control due to this can be suppressed.

In this way, the VCM driving target signal (second movement amount target signal) is created. In addition, this V
The CM drive control signal is used to generate a feedforward control signal (first movement amount target signal) described later. However, when the measurement position D becomes the exposure position F, that is, when the measurement position D is exposed, the VCM drive control signal is used as a feedback signal.

Next, as shown in FIG. 7C, the phase of the VCM driving target signal is advanced by the phase amount d to generate the feedforward control signal. 8 (a) and 8 (b)
3 is a response frequency graph of the lens unit 60. FIG. 8A is a graph showing the response of the gain (movement amount of the lens unit) with the vertical axis representing the gain and the horizontal axis representing the frequency, and FIG. 8B is the graph representing the vertical axis representing the phase. 6 is a graph showing the response of the phase of the lens unit with the frequency plotted on the horizontal axis. In addition, in FIG. 8A, the movement amount of the lens unit 60 is shown by a gain. In addition, FIG.
The scale intervals on the horizontal axis in (b) are the same. Figure 8
As shown in (a) and (b), the lens unit 60
In terms of the lens movement amount (gain) and the phase, the followability is worse in phase, and the lens unit 60 does not follow the movement amount of the lens unit 60 earlier. Therefore, it is necessary to adjust the phase. At this time, the phase shift of the lens unit 60 is
It is determined by the configuration of the exposure head 40. For example, in order to obtain a response of 200 Hz, it is necessary to advance the phase by 1 millisecond.

In the signal processing shown in FIGS. 7A to 7C, the feedforward control signal is created using the cylindrical drum displacement data for one revolution immediately before exposure.
The present invention is not limited to this. For example, when the measurement position D of the drum displacement measuring sensor 70 is set two lines before, the feedforward control signal may be created based on the average data of the cylindrical drum displacement data for two revolutions.

The AF control circuit 150 generates a control signal such that the distance between the drum 30 and the lens unit 60 becomes the focal length on the basis of the VCM driving target signal and the feedforward control signal, and the VCM driving is performed. Circuit 1
It is output to 60. FIG. 9 is a block diagram showing an AF control circuit in the autofocus system. As shown in FIG. 9, the AF control circuit 150 uses the VCM
It has an inverse system 152, an amplifier 154, an amplifier 156 and a VCM system 158.

The VCM reverse system 152 receives a feedforward control signal and calculates an output signal required to move the VCM by a predetermined amount based on the feedforward control signal. Amplifier 154
Is connected to the VCM reverse system 152,
It amplifies the output signal of the inverse system 152 and outputs the amplified output signal to the VCM system 158. The amplifier 156 is a displacement calculation and waveform shaping circuit 13.
VCM driving target signal by VCM system 8 and VCM system 15
The deviation signal, which is the difference from the output signal of No. 8, is input and the deviation signal is amplified. VCM system 158
Is for calculating the movement amount of the VCM 50 based on the deviation signal and the feedforward control signal.

The VCM drive circuit 160 is the AF control circuit 1
The drive amount of the VCM 50 is determined in consideration of the output signal (lens position information) of the lens displacement calculation circuit 136 in the output signal of 50, and the drive signal corresponding to the drive amount is output to the VCM 50.

Next, the operation of the image recording apparatus of this embodiment will be described. 10A to 10C are schematic views showing the exposure method of the image recording apparatus of this embodiment in the order of steps.
First, the transport unit 108 moves the recording medium P to the drum 3
Supply to 0. Next, the recording medium P is formed on the outer peripheral surface of the drum 30.
Are fixed by the front end chuck 34 and the rear end chuck 36. Next, the exposure head 40 is moved to the exposure preparation position. Next, the main scanning motor 22 is driven to rotate the drum 30 at a predetermined rotation speed.

Next, after the drum 30 reaches a predetermined number of revolutions, as shown in FIG. 10A, the drum displacement measuring sensor 70 (see FIG. 5A) provided on the exposure head 40 The distance between the recording medium P and the exposure head 40 is measured. As described above, the measurement position of the drum displacement measuring sensor 70 is downstream of the light beam B emitted from the lens unit 60 of the exposure head 40 in the sub scanning direction M. In this case, the focal position of the lens unit 60 of the exposure head 40 is the surface of the drum 30. In this way, before the start of exposure, the variation of the recording medium P to be exposed in advance is measured from the edge along the sub-scanning direction M. Then, as described above, the processing shown in FIGS. 7A to 7C is performed from the measurement data (drum displacement information) of the recording medium P that has not been exposed to determine the size of the plate and the front end chuck 34 and the rear end. The position of the chuck 36 is specified and a feedforward control signal is generated. As a result, the autofocus control can be started.

Next, as shown in FIG. 10B, while the exposure head 40 is being conveyed in the sub-scanning direction M, the above-mentioned autofocus control using the cylindrical drum displacement data immediately before the exposure is performed and a predetermined image is displayed. The data is recorded on the recording medium P. Next, FIG.
As shown in 0 (c), since the measurement position of the drum displacement measurement sensor 70 is on the downstream side of the exposure position of the exposure head 40, even if the drum displacement measurement sensor 70 finishes measuring the displacement of the recording medium P. , Exposure does not end. Therefore, when the measurement position of the drum displacement measuring sensor 70 has passed the recording medium P, the measurement data is the displacement calculation and waveform shaping circuit 13.
8 memories. Then, based on the measurement data stored in the memory, the displacement calculation and waveform shaping circuit 1
At 38, a feedforward control signal is generated, and the edge of the recording medium P is exposed while performing the autofocus control.

Next, after the exposure is finished, the irradiation of the light beam B is stopped and the rotation of the drum 30 is stopped. Next, the drum 30
After stopping, the front end chuck 34 and the rear end chuck 3
The constraint of 6 is released, and the recording medium P is removed from the drum 30. Next, the recording unit P is carried out by the carrying unit 108.

As described above, in this embodiment, the displacement of the scan line (measurement position D) of the drum 30 immediately before the exposure measured by the drum displacement measuring sensor 70 and the exposure scan exposed by the lens unit 60. Since the displacement of the line (exposure position F) is almost the same, the feedforward control signal used for position control of the lens unit 60 at the time of exposure is used by using the drum displacement data of the scanning line immediately before exposure. To generate. Then, by controlling the position of the lens unit 60 by combining the feedforward control using the signal for feedforward control and the feedback control, the feedback control is performed in a state where the behavior of the lens unit 60 in the main scanning direction is known in advance. can do. Therefore, without increasing the movement amount and the response speed of the lens unit 60,
The focal length of the distance between the lens unit 60 and the recording medium P can be maintained without the phase delay. Accordingly, at the exposure position F, a predetermined image can be accurately recorded on the recording medium P while maintaining a predetermined beam spot diameter.

Therefore, when a line is recorded on the recording medium P using the image recording apparatus 10 of this embodiment, the line width does not become thin due to defocusing as shown in FIG. Therefore, when halftone dots are recorded on the recording medium P, the line width does not become thin, so the area ratio of halftone dots does not change, and the density shift of the printed matter due to this does not occur.
Therefore, when printing is performed using the produced plate, it is possible to obtain an image having a desired image quality without uneven density.

As described above, in this embodiment, the lens unit 60 can be controlled with good followability without delaying the phase. Therefore, even if the beam spot diameter is reduced, the image can be accurately displayed with an appropriate spot diameter. Can be recorded. Thereby, even a high-definition image can be recorded with a desired image quality. Further, in the present embodiment, even if the beam spot diameter is reduced, an image can be recorded with an appropriate spot diameter.
Even with a recording medium P having low sensitivity such as a plate, an image can be accurately recorded by reducing the beam spot diameter and increasing the energy density.

Further, in this embodiment, it is not necessary to increase the responsiveness of the feedback control, so it is not necessary to increase the rigidity of the lens guide mechanism and the like. Therefore, it is possible to suppress the increase in the mass of the exposure head 40, and it is not necessary to increase the thrust of the actuator. As a result, it is possible to prevent the exposure head 40 from increasing in size,
The cost increase of the device can be avoided.

Further, in the lens guide mechanism of the exposure head 40 of this embodiment, the lens unit 60 is placed on the swinging member 51 which moves by the parallel link, and this parallel link is driven by the VCM 50, whereby the lens unit. The recording medium 60 can be moved toward or away from the recording medium P. The swing plates 58 and 59, which are parallel link elements, are, for example, strip-shaped first elastic pieces 56a and second elastic pieces 56.
The lens unit 60 is connected by b, and can be easily moved. Therefore, even if the thrust of the VCM 50 (actuator) is small, the lens unit 60 can be moved with good responsiveness.

In the image recording apparatus 10 of this embodiment, the arithmetic operation in the control section 100 is performed by a digital signal processor (DSP).
It is preferably a digital operation according to r). As a result, the calculation processing speed can be increased. The image recording apparatus 10 of the present embodiment is an image recording apparatus that holds the recording medium P on the outer peripheral surface of the drum 30 and uses a so-called outer drum. However, the present invention is not limited to this, and may be a so-called inner drum type image recording device that holds the recording medium on the inner peripheral surface of the cylindrical drum. In addition to the drum scanner, the light beam modulated according to the recorded image is deflected in the main scanning direction, and the recording material is conveyed in the sub-scanning direction orthogonal to the main scanning direction, so that the recording material is two-dimensionally processed. Image recording may be performed by so-called raster scanning, in which scanning exposure is performed selectively.

Although the image recording apparatus of the present invention has been described in detail above, the present invention is not limited to the above-described embodiments, and various improvements and changes can be made without departing from the gist of the present invention. Of course, you can.

[0071]

As described in detail above, according to the present invention, a control signal for driving the actuator is generated from the drum displacement data immediately before the exposure by the waveform calculation so that the distance between the drum and the lens becomes the focal length. By doing
The position of the lens unit can be controlled after the state of the exposure position is known in advance. Therefore, the distance between the lens unit and the drum can be controlled to be the focal length without improving the responsiveness of the lens unit. This can solve the problem that the phase is delayed. Further, in the present invention, since it is not necessary to increase the responsiveness, it is not necessary to increase the rigidity of the lens guide mechanism and the like. For this reason, since the increase in the mass of the controlled object is suppressed, it is not necessary to increase the thrust of the actuator, and the cost increase of the device can be avoided. Further, according to the present invention, since an image can be recorded while maintaining a proper beam spot diameter, it is possible to obtain a printed matter having high image quality without uneven density. Further, even when the beam spot diameter is made small, the image can be recorded while maintaining the beam spot diameter, so that a high-definition image can be recorded.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an image recording apparatus (outer drum type printing plate exposure apparatus) according to an embodiment of the present invention.

FIG. 2 is a side view of the image recording apparatus of this embodiment.

FIG. 3 is a perspective view showing an exposure head of the image recording apparatus of this embodiment.

FIG. 4 is a side view seen from the direction A in FIG.

5A is a schematic diagram showing an exposure position of a lens and a measurement position of a drum displacement measuring sensor, and FIG. 5B is a schematic diagram showing a configuration of a drum displacement measuring sensor.

FIG. 6 is a block diagram showing an autofocus system of the image recording apparatus of this embodiment.

FIG. 7 is a graph showing a method of generating a feedforward control signal and a VCM driving target signal by a displacement calculation and waveform generation circuit in the order of steps, in which (a) shows displacement on the vertical axis and time on the horizontal axis. The drum displacement data is shown in (b), the vertical axis shows the output, and the horizontal axis shows time.
FIG. 6C is a graph showing a CM drive target signal, and FIG. 7C is a graph showing a feedforward control signal with the output on the vertical axis and the time on the horizontal axis.

FIG. 8A is a graph showing the response of the gain (movement amount of the lens unit) with the vertical axis representing the gain and the horizontal axis representing the frequency, and FIG. 8B is the vertical axis representing the phase. 4 is a graph showing the response of the phase of the lens unit, with the horizontal axis representing frequency.

FIG. 9 is a block diagram showing an AF control circuit in the autofocus system.

10A to 10C are schematic diagrams showing the exposure method of the image recording apparatus of this embodiment in the order of steps.

FIG. 11 is a graph showing the difference in the intensity distribution of the light beam depending on the focal length, with the horizontal axis representing the surface direction and the vertical axis representing the light intensity.

FIG. 12 is a block diagram showing a conventional autofocus control device.

[Explanation of symbols]

10 Image recording device 12 bases 14 Guide 16 Support member 22 Main scanning motor 26 rotary encoder 28 Sub-scanning motor 30 drums 34 Tip chuck 36 Rear end chuck 40 exposure head 50 Voice coil motor (actuator) 60 lens unit 70 Drum displacement measurement sensor 80 Lens position measurement sensor 90 light source 100 control unit 102 Main scanning motor driver 104 Sub-scanning motor driver 106 Mechanical control circuit 108 Transport unit 110 AF system circuit 120 Synchronous circuit 130 Auto Focus System 150 AF control circuit 160 VCM drive circuit D measurement position F exposure position M sub-scanning direction P recording medium

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/036 1/06 F term (reference) 2C162 AE04 AE23 AE28 AE48 AE57 AF13 AF25 AF82 FA04 FA17 FA18 FA54 FA59 FA67 FA70 2H045 AG09 CB04 DA21 2H051 AA10 BB20 BB24 5C051 AA02 CA07 DB22 DB30 DE22 5C072 AA03 DA02 DA23 HA02 JA02 JA07 JB01 UA13 XA03

Claims (5)

[Claims] 1. A surface of a recording medium wound around an outer surface of a drum that rotates at a constant speed is main-scanned by a light beam in the drum rotation direction by an exposure unit, and the exposure unit is moved in the axial direction of the drum. An image exposure apparatus that two-dimensionally exposes an image by performing sub-scanning while moving along, wherein the exposure unit includes a housing arranged to face the drum, and a first housing in the housing. A pair of parallel members that are connected via elastic members and are capable of swinging with respect to the drum while maintaining a parallel state, and a swing member connected to the parallel members via a second elastic member. A lens unit that is mounted on the swing member and focuses a light beam on the surface of the recording medium; and an actuator that moves the swing member toward or away from the drum. Image exposure device. 2. The image exposure apparatus according to claim 1, wherein
Further, a displacement measuring unit that measures a displacement of the recording medium wound around the rotating drum at a downstream side in the sub-scanning direction with respect to a light beam imaging position of the exposure unit, and the lens unit. And an lens position measuring unit for measuring the position of the image exposure device. 3. An exposure unit causes a light beam to perform main scanning in a drum rotation direction on a surface of a recording medium wound around an outer surface of a drum rotating at a constant speed, and the exposure unit is moved along an axial direction of the drum. Is an image exposure method of performing two-dimensional exposure of an image by sub-scanning while moving by moving the recording medium, the displacement of the recording medium immediately before exposure on the downstream side in the sub-scanning direction with respect to the image forming position of the light beam. A step of measuring, a step of generating a movement amount target signal for moving a lens unit that forms an image of the light beam on the surface of the recording medium by waveform calculation from displacement data of the recording medium immediately before the exposure; Exposing the image by moving the lens unit based on a target signal. 4. The surface of a recording medium wound around the outer surface of a drum rotating at a constant speed is mainly scanned in the drum rotating direction by a light beam by an exposure unit, and the exposure unit is moved along the axial direction of the drum. Is an image exposure method of performing two-dimensional exposure of an image by sub-scanning while moving by moving the recording medium, the displacement of the recording medium immediately before exposure on the downstream side in the sub-scanning direction with respect to the image forming position of the light beam. A step of measuring, and a step of generating a first movement amount target signal for feedforward control and a second movement amount target signal for feedback control by waveform calculation from displacement data of the recording medium immediately before the exposure, Displacement data of the recording medium at the time of exposure is used as a feedback signal, and the feedback signal, the first movement amount target signal and the second movement amount target Generating a focusing target value signal of the lens unit for focusing the light beam on the surface of the recording medium based on a signal, and exposing the image by moving the lens unit based on the focusing target value signal. An image exposure method comprising: 5. The waveform calculation is a calculation for removing high-frequency noise of displacement data of the recording medium, a calculation for removing data in a fixing means for fixing the recording medium to an outer surface of the drum, the fixing means, and The image exposure method according to claim 3, further comprising an operation of replacing data of a portion of the drum where the recording medium does not exist with data of a leading end portion of the recording medium, and an operation of advancing a phase of the displacement data.