JPH02105110A - Scanning method for plural beams - Google Patents

Abstract

PURPOSE:To enable fast plotting without being affected by interference between plural beams by forming N spots on a plotting screen with N beams at intervals in a subscanning direction, scanning those spots in a main scanning direction at the same time, and scanning an (Li)th line where an (i)th beam is specified in an (n)th scan. CONSTITUTION:The N spots are formed on the plotting screen with the N beams at intervals in the subscanning direction and scanned in the main scan ning direction at the same time, and the (Li)th which is determined by an equa tion I is scanned with the (i)th beam in the (n)th scan. In the equation, N>=2, 1<i<=N, and k1=0, where ka is a constant for determining the quantity of isolation between lines scanned simultaneously with the (m)th beam and (m-1)th beam. Consequently, the interference between the plural beams is prevented and the merit of a fast plotting speed is utilized sufficiently.

Description

[Detailed Description of the Invention] [J! ! Field of Industrial Application] The present invention relates to a device such as a laser printer or a laser photoplotter that performs drawing by scanning a spot on a drawing surface, and particularly to a scanning method in a device that scans a plurality of beams.

[Problem to be solved by the invention] When drawing, it is better to draw multiple lines at the same time using multiple beams than to write each line using a single beam. Even when the speed is slow, it is possible to perform high-speed drawings.

Also, the distance between the - line and the adjacent line is
In order to perform precise drawing, the spot diameter may be set smaller than the spot diameter, and in such cases, when adjacent lines are scanned in parallel as shown in Figures R and 2, the overlapping area shown by diagonal lines will appear. The beam intensity is distorted due to interference.

Note that the same beam in the main scanning direction moves in time series, so no interference occurs. Here, the main scanning direction refers to the direction in which the beam scans on the drawing surface, and The scanning direction refers to a direction perpendicular to the main scanning direction on the drawing surface.

Generally, one summer of exposure in the overlap area is expressed by the formula 0, 1:li*(7)+i・(y+Δy)I"...0
If the spots of the two beams are spatially or temporally separated and do not interfere, the sum of the intensities is a simple sum as shown in equation (2).

1=li*(y)Ikan+1ta(y+Δy)l=I^
(y)+l5(y÷Δy) . . . However, when the overlapping portions are simultaneously irradiated, an interference term feat is included in addition to the simple intensity sum, as shown in equation (2).

11L(y)l”÷1ie(y÷Δy)l”+1a(y
)−is”(y+Δy)÷l＾°(y)・1t(y+Δy
y) :I^(y)+i・(y×Δy)÷! 1r*...
・■ Note that the interference term feat is expressed by equation 0.

flat・1s(y)is”(31+Δy)+i11°
(y)is(y+Δy)・・・■The interference term is ill and 1-
It takes different values depending on the phase difference φ between the two. Moreover, this phase difference φ is not constant over the entire scanning area due to wavelength-order aberrations and errors of optical members such as fθ lenses and mirrors, and optical path differences caused by temperature changes, vibrations, etc. The change in angle causes different interference conditions depending on the location on the drawing surface.

As a result, what should normally be recorded on the drawing surface with two lines uniformly aligned by the human pot formed by the two beams, becomes -1 thick line, or conversely, each line becomes too thin. Or, in some cases, the result appears to be that three beams are scanning, and the drawing result becomes unstable.

To avoid this, it is necessary to space the scanned spots in the sub-scanning direction so that they do not overlap on the drawing surface, but simply increasing the space between adjacent lines will reduce the recording density and reduce precision. It is no longer possible to draw a picture.

In order to eliminate the influence of interference without reducing the drawing accuracy, it is necessary to avoid spacing the scan lines in the sub-scanning direction that are drawn as a result, and to draw spots that are formed simultaneously during drawing instead of adjacent lines. A configuration in which one or more M lines are scanned is conceivable.

However, if the interval between simultaneous scans is one line, the shift in the sub-scanning direction between the first scan and the second scan will be one line, and in the first scan, the first and third lines,
The second and fourth lines overlap in the second scan, and the third and fifth lines overlap in the third scan, so that the third and subsequent lines overlap.

In order to avoid duplication, one beam may be turned off during the third and subsequent scans, but in this case, the advantage of high-speed scanning using multiple beams is essentially lost.

[Objective of the Invention] The present invention has been made in view of the above-mentioned problems, and improves the drawing accuracy by making the interval between adjacent scanning lines output as a result of drawing smaller than the spot diameter. It is an object of the present invention to provide a multiple beam scanning method that can achieve high-speed writing using multiple beams without being affected by interference.

[Means for Solving the Problems 1] In order to achieve the above object, the present invention forms N spots spaced apart in the sub-scanning direction on the drawing surface using N beams, and simultaneously focuses these spots on the main scanning direction. Scanning is performed in the scanning direction, and in the n-th scan, the first beam is expressed by formula (A). It is characterized in that the Lith line determined by a constant for determining the distance between the lines is scanned.

The optical system of the device for carrying out this method includes a light source that generates multiple beams, a deflector such as a polygon mirror that deflects the beams from this light source, and focuses the deflected beams onto the drawing surface. A scanning lens such as an fθ lens is provided.

In order to obtain multiple beams, a multi-point emitting laser element may be used, or a beam emitted from a single light source may be divided. These beams are drawn at predetermined line intervals. The incident angles in the sub-scanning direction with respect to the scanning lens are set to be different so as to form a spot on the surface.

The simplest combination that satisfies formula (A) above is to use two beams, set the interval during simultaneous scanning to 3 lines as shown in Figure 1, and scan - times and the next scan. The configuration is such that the amount of movement between the two lines is three lines.

According to this configuration, N:2, Kal, and the line scanned by the first beam during the nth scan is the first line.
As shown in the table. Note that the interval between the m-th beam and the m-1-th beam that are scanned simultaneously is 1[m+1
It can be expressed as

Table 1 According to this method, the third and subsequent lines are continuous lines,
In other words, it becomes a line that can be used for drawing, and the first
, the second line is a dummy scan.

Next, when K2=2, the results are as shown in Table 2. In Table 2, the lines starting from the 5th line are continuous,
The first to fourth lines are dummy scans.

In this way, the smaller the value of K, the fewer the lines to be dummy scanned, but depending on the relationship between the spot diameter and the distance between lines in the sub-scanning direction, it may be set to 2 or more to avoid interference. can.

Next, a case where simultaneous scanning is performed using three beams (N=3) will be explained. In this case, the distance between the first and second beams and the distance between the second and third beams may take different values, so when scanning n[1ilEj, the first beam scans Here are three examples of lines.

First, if K*=Ks=1, then the result is as shown in Table 3, and if e"l[s:2, then Table 4, and Mo*:
2. In the case of Ih:1, the results are as shown in Table 5.

Table 3 Table 4 Table 5 By the way, when scanning as described above, the order of scanning and the order of scanning lines do not correspond as in the case of scanning with a single beam, so the image data is output as is in the address order. However, it is not possible to draw an output image that matches the data.

Therefore, it is necessary to adopt a method of writing image data output in address order into a -H line memory and outputting image data corresponding to a scanning line number from the line memory to perform drawing.

The size of the line memory is determined by the number N of scanning beams and the above constant.

Here, as shown by the rectangles in Figures 2 to 5, an area for storing N942 consecutive pieces of data is designated as one part of the line memory.
If it is a group, the data within l group is BuyP=1+ΣK.

Crow: 2 The entire image is output by P scans expressed as P times.

Since the data output of one group and the data output of the following group are sequentially shifted by l scans, the number of line memory groups required is two, and the total memory size can be expressed as P-N. can. According to this calculation, in the method shown in Figure 2, two groups will cover 4 lines from ■ to ■, and in the methods shown in Figures 3 and 4, three groups will cover 6 lines from ■ to In this method, the total memory size is 15 lines (■ to ■) in five groups. Note that rdJ in the figure indicates dummy scanning.

In addition, data in each group is output in order from the address with the largest address as image data, contrary to normal single beam scanning.For example, when scanning with the method shown in Figure 4, the data on the drawing surface is The data from the 7th line to the 9th line is read from the image memory in this order, but when outputting, this is reversed, that is, the 9th line is read in the first scan, the 8th line is read in the second scan, and the data is read in this order from the image memory. The data of the seventh line will be output in the third scan.

When all the data in one group is output through two scans, image data for the next N scans is input to the lines of that group. Then, all the data of the next group is also output through P+1 scans, and new image data corresponding to N scans is input to that group as well. In this way, new image data is written to the memory of the group that has finished outputting each time it is scanned, and by outputting this data in the reverse order of input within the group, an image according to the image data is drawn. be able to.

[Example] The present invention will be described in detail below.

FIG. 6 shows an embodiment of an optical system of a laser photoplotter for realizing the multiple beam scanning method according to the present invention.

This photoplotter splits the laser light emitted from the argon laser lO as a light source into three beams, two of which form two spots on the drawing surface, and the remaining one to accurately position the spot. It is used as a monitor light to detect. The two spots formed on the drawing surface are separated by five lines due to the rotation of the polygon mirror PM, and simultaneously scan the scanning lines.

That is, according to the above explanation, N=2. The configuration is such that Kz = 2, the spot diameter is 5 μm, the pitch of the scanning line in the sub-scanning direction is 2.5 μm, and therefore the center distance between the two spots is 12.5 μm. will be 5 μl.

Next, the configuration of each part of this device will be explained along with its operation.

Laser light emitted from the argon laser IO is split into two by a half mirror 12 with 5% reflection via a pinhole 11. The laser beam reflected by this half mirror 12 is used as a monitoring luminous flux g.

On the other hand, the laser beam transmitted through the half mirror 12 has its polarization direction rotated by 90 degrees by the first 172-wavelength plate 13, and the light intensity is adjusted by the barrier pull filter 14 to reflect 50%, 0%, and 1
The beam splitter 15 further divides the beam into two.

The two beams of light split by the beam splitter 15 are used as a drawing light beam that forms two spots separated on the drawing surface.

First drawing light flux II transmitted through beam splitter 15
is focused on the position of the first drawing AO modulator 17 via the lens 16.

This AO modulator 17 diffracts the laser beam incident from the direction satisfying the Bragg condition by inputting the ultrasonic wave to the transducer, and converts the input ultrasonic wave to 0N.
By performing 10FF, the laser beam can be switched to zero-order light and first-order light, and the first-order light is used as a drawing light beam. The AO modulator 17 is controlled by a write signal which is dot-by-dot exposure information for the drawing surface.

The primary light, which is the modulated ON light, is made into a parallel light beam again by the lens 1B provided behind the AO modulator 17, and then passed through the mirror 19 to the first light beam direction adjusting device 40 consisting of two prisms. is deflected at a predetermined angle by mirror 2.
0, the light enters the lun system 50.

On the other hand, the second beam reflected by the first beam splitter 15
Luminous flux for drawing! 2 is made into a convergent light through a lens 16', reflected by a mirror 21, and transmitted to a second drawing AO modulator 17-
incident on . The function of the AO modulator 17' is similar to that of the first drawing AO modulator 17 described above. However, this second
The signal that drives the drawing AO modulator 17' is the first signal that drives the drawing AO modulator 17'.
The signal input to the drawing AO modulator 17 is a signal for scanning lines shifted by 5 lines.

The primary light emitted from the second drawing AO modulator 17' is deflected by a predetermined angle by a second beam direction adjustment device 40' made up of two prisms through a lens 1B-, and then enters the lens system 50.

Note that the eleventh and second drawing light beams 11 and 'JR have an angle of 0.17'' to each other in the sub-scanning direction and are 2.4
The light enters the second lens system 70 from a position separated by mm. Further, lenses 16.18= and 18.18'' are the same lens, and their focal length is 130.02 mm.

The lens system 50 is a positive lens with a focal ratio of M179.99 mm, and converges the incident laser beam. A correction AOO adjuster 22 is provided 61.951101 points before the focal point of the first lens system 50 to correct the influence of the surface tilt of the polygon mirror PM.

The drawing laser beam emitted from the correction AO transformer 2 and reflected by the mirror 23 passes through the relay lens system 60 with a focal length of 56.18 m+o, and has a focal ratio of 11299.99.
The light is incident on the second lens system 70 of mm.

The relay lens system 60 has a function of correcting the deviation of the light beam on the polygon mirror due to the surface tilt correction by the correction AOO adjuster 22.

The laser beam for drawing, which is made into a parallel beam by the second lens system 70, is reflected by the mirror 24 and combined with the monitor light by the first polarizing beam splitter 25. That is, the monitor light 9 divided by the half mirror 12
. is reflected by the mirrors 26 and 27, enters the first polarizing beam splitter 25 as S-polarized light, and is reflected.

On the other hand, the two drawing light beams are made to have a polarization direction different from that of the monitor light by the first 172-wave plate 13, and are incident as P-polarized light, so that they are transmitted as they are. The polarization directions of the two drawing light beams and the monitoring light beam are each rotated by 90'' by the second 172-wavelength plate 28, and then passed through a third lens system (equipment) with a focal length of -16 and 16 mm and a mirror 29. and enters the fourth lens system 90 with a focal length of 346.22 mm.

The third lens system 80 and the fourth lens system 90 have a magnification of 21.
A 4x beam expander system is constructed, and the two drawing light beams are expanded to 25φ, and the monitoring light beam is expanded to 15φ.

The two drawing light beams and the monitoring light beam are directed to a polygon mirror PM via two mirrors 30 and 31, and are reflected and deflected by this polygon mirror I'H.

This reflected light beam has a focal ratio of 11151.21a+
The drawing light beam is converged by the f-theta lens 100 of m and passes through the second polarizing beam splitter 32 to form two spots each having a diameter of 5 μm on the drawing surface.

On the other hand, the monitor light is reflected by the beam splitter 32 and enters the light receiving optical system 34 via a scanning correction scale 33 having a cotton-like pattern perpendicular to the scanning direction. The light receiving optical system 34 outputs a pulse having a frequency proportional to the scanning speed based on the amount of light transmitted through the scale 33, which changes as the beam scans.

The two spots formed on the drawing surface are formed at the same position in the main scanning direction and at a distance of 12.5 μm, which is an interval of 5 lines, in the sub-scanning direction.

In addition, three light receiving elements for autofocus are provided opposite the light receiving optical system 34 with the second deflection beam splitter 32 in between, and the optical system uses the state of reflected light at each scanning position. The state of focus on the drawing surface is detected and used as data for automatic focusing.

[Effect] As explained above, according to the present invention, when a plurality of spots spaced apart in the sub-scanning direction are formed on the drawing surface and scanned simultaneously, the drawing performance is improved by preventing interference between the plurality of beams. It is possible to stabilize the drawing speed and take full advantage of the increased writing speed due to multiple beam scanning.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of scanning lines on a drawing surface in the multiple beam scanning method according to the present invention, FIGS. 2 to 5 are explanatory diagrams showing the relationship between scanning line numbers and line memories, and FIG.
The figure is an explanatory diagram showing an embodiment of the apparatus for carrying out the present invention, No. 75! 1 is an explanatory diagram when adjacent scanning lines are simultaneously scanned, and FIG. 8 is a diagram of the beam intensity distribution along the line ■-■ in FIG. 7. lO...Argon laser (light source) PM...Polygon mirror (deflector)

Claims (1)

[Claims] N spots spaced apart in the sub-scanning direction are formed on the drawing surface by N beams, and these spots are simultaneously scanned in the main-scanning direction, and the i-th spot is scanned at the n-th scan. The beam of
≧2 l≦i≦N k_l=0 k_m: Natural number, m-th beam and m-th beam of simultaneous scanning
A multi-beam scanning method characterized by scanning the Lith line determined by a constant for determining the amount of separation between the lines scanned by the first beam.