JP2675695B2 - Light intensity control method for scanning beam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling the light quantity of a light beam deflected by a light deflection element. More specifically, it is a technique applied to a high-speed drawing device or the like that scans a photosensitive material such as a photosensitive film or a glass plate with a light beam deflected by an optical deflecting element using an acousto-optical element. By appropriately correcting the control signal applied to, the fluctuation of the light quantity of the scanning beam is eliminated.

[0002]

2. Description of the Related Art As is well known, an AOD (acousto-optic deflector) having an acousto-optic medium such as tellurium dioxide single crystal and a piezoelectric element adhered to one side surface of the acousto-optic medium is an acoustic deflector that changes the path of light. Has optical effect. That is, when a transverse ultrasonic wave is generated by applying an electric signal to the piezoelectric element and the transverse ultrasonic wave is propagated in the medium, the laser beam passing through the medium is diffracted by the periodic fluctuation of the refractive index in the medium. Especially,
The first-order diffracted light of Bragg diffraction is put to practical use because of its high diffraction efficiency. Moreover, since the diffracted direction is proportional to the frequency of the ultrasonic wave, if the AOD is used, the direction of the light can be controlled by frequency modulation. Based on such characteristics, the AOD is widely used as an optical deflection element for image recording devices and the like.

However, since the intensity of the diffracted light, that is, the amount of light changes depending on the frequency of the transverse ultrasonic wave, the ultrasonic wave having a constant amplitude and the frequency of which fluctuates periodically is propagated in the acousto-optic medium. Then, the amount of diffracted light varies depending on the diffracted direction. Therefore, when the photosensitive material is exposed by scanning the photosensitive material with diffracted light, the amount of exposure light varies depending on the scanning position on the photosensitive material, so that the image density cannot be recorded on a fixed basis.

As a technique devised as a method for solving such a problem, there is one disclosed in Japanese Patent Laid-Open No. 59-160128. That is, the technology is AOD
Amplitude of ultrasonic waves is adjusted appropriately for each frequency so that the amount of diffracted light diffracted by (hereinafter, diffraction is generally called deflection) is always the maximum amount (diffraction efficiency is the highest). Is what you are trying to do. As such an adjusting means, a bandpass filter whose passband characteristic is appropriately designed is used.

FIG. 14 is a block diagram schematically showing the electrical configuration of the technique. As shown in the figure, the output of a voltage controlled oscillator (hereinafter referred to as VCO) 14 is passed through a bandpass filter 18 to an amplifier (hereinafter referred to as amplifier) 1
9 is input. As a result, the frequency signal oscillated by the VCO 14 is attenuated by a different amount for each frequency according to the attenuation characteristic of the bandpass filter 18, and the amplifier 19 drives the drive signal V based on the attenuated frequency signal.
_d is added to AOD2. Accordingly, by appropriately adjusting the damping characteristics of the band-pass filter 18, it is possible to keep the amount of the deflected laser beam L _d by AOD2 a constant level. Such a bandpass filter 18
The attenuation characteristic of is set as follows.

That is, by changing the frequency and power of the drive signal V _d of the AOD 2 in advance, the light quantity of the deflected laser beam L _d is measured, and the deflection efficiency (incident laser beam L _i
Let PI be the light amount of P and the light amount of the deflected laser beam L _{d be} P, and the deflection efficiency is expressed by P / PI. ). Then, when the electric power of the drive signal V _d that maximizes the deflection efficiency is obtained for each frequency from the obtained data, FIG.
As shown in, the relationship between the power of the drive signal and its frequency is approximated by a quadratic curve. Therefore, the filter should be designed so that the attenuation characteristic of the bandpass filter 18 corresponds to the quadratic curve of FIG.

[0007]

Since the conventional technique is constructed as described above, it certainly has an advantage that the fluctuation of the light quantity of the deflected beam can be suppressed. But AO
Since a bandpass filter is used as the power correction means for the D drive signal, the following problems have occurred.

First, in the present correction method,
Assuming that the power of the drive signal and the light quantity of the deflected beam are linear, the relationship between the power of the drive signal and the frequency is 2
Although it is approximated by the following curve, the power of the drive signal and the light quantity of the deflected beam have a non-linear relationship in reality. Therefore, when the light quantity of the deflected beam is actually measured, the obtained maximum deflection efficiency does not become an ideal straight line as shown by the broken line in FIG. 16, but actually becomes a curved line as shown by the solid line in FIG. As described above, this correction method has a problem in principle that the fluctuation of the light quantity of the deflected beam cannot be sufficiently suppressed.

Secondly, the present technology has a problem that it is difficult to realize a filter characteristic that faithfully reflects the curve showing the relationship between the power and frequency of the drive signal. That is, the relationship between the power of the drive signal and the frequency cannot always be accurately approximated by a quadratic curve as shown in FIG.
When the curve showing the relationship between the two is expressed as a function that is slightly modified from the quadratic curve, for example, as a function form shown by the solid line in FIG. 17A, the attenuation characteristics reflecting such a function form are shown. It is not easy to construct a filter with Even if it is realized by a filter having a general structure, there is a drawback that the circuit structure becomes complicated.

Further, when an extreme deflection efficiency change occurs at a specific frequency, the correction method cannot cope with such a change. For example, as shown in FIG. 17B, when it is necessary to drastically change the power at a specific frequency, it is impossible to create such a drive signal due to the attenuation characteristic of the filter.

As described above, in the present correction method, when the relationship between the power and frequency of the drive signal changes in various ways (these changes are caused by variations in the characteristics of the AOD itself), such a change occurs. It can be said that we cannot flexibly respond to changes.

Thirdly, the present technique also has a problem that it takes a lot of time and labor to measure the deflected beam and adjust the attenuation characteristic of the filter, and the drive signal cannot be corrected quickly. There is.

Fourthly, the present technology has a problem that it cannot flexibly respond to changes in environmental conditions such as temperature changes. That is, since the characteristics of the AOD change depending on the change of the ambient temperature, the deflection efficiency of the light deflected by the AOD also depends on the change of the ambient temperature. Therefore,
Although it is necessary to adjust the power of the drive signal according to the temperature change, the method of adjusting the power of the drive signal by the attenuation characteristic of the filter as in the present technology follows the fluctuation of the deflection efficiency due to the temperature change, Delicately controlling the damping characteristics is a difficult technique. Of course, the characteristics of the filter itself also change depending on the temperature, which makes the above control more difficult.

As described above, the various problems described above are caused by the fact that the present technique uses a bandpass filter as the power correcting means.

The present invention has been made to solve such a problem, and an object thereof is to keep the light amount of the scanning beam deflected by the optical deflecting element at a constant level regardless of the scanning position. Therefore, it is an object of the present invention to provide a method for controlling the light quantity of a scanning beam, which can easily perform correction for the above, and can flexibly cope with changes in environmental conditions and variations in element characteristics.

[0016]

A first structure of the present invention is a scanning for scanning a light beam by using a light deflecting element which deflects the light beam according to a control signal and changes its deflection angle. The present invention relates to a method for controlling the light quantity of a beam. That is,
(A) The frequency and amplitude of the control signal are changed within a predetermined range to measure the light quantity of the scanning beam, and the first scanning beam
Get the light intensity data of. Then, (b) from the first light amount data, the maximum value of the light amount of the scanning beam is obtained for each frequency of the control signal within a predetermined range of the frequency within a predetermined range regarding the frequency, and c)
The light amount value that is the minimum value is obtained in the data of the maximum value of the light amount obtained for each value of the frequency, and the minimum value is multiplied by a predetermined constant value for correction. Further, (d) for each frequency of the control signal within the effective range, step (c)
The amplitude of the control signal that gives the light amount value obtained in step (b) is obtained from the first light amount data obtained in step (b),
(E) The light beam is scanned while driving the optical deflecting element based on the amplitude data of the control signal for each frequency obtained in step (d).

Moreover, in the first configuration of the present invention, the above step (e) is performed based on the amplitude data of the control signal for each frequency obtained in (e-1) step (d). The second light amount data of the scanning beam is obtained by scanning the light beam and measuring the light amount of the scanning beam, and (e
-2) The minimum value of the light amount in the effective range is obtained from the second light amount data, and (e-3) the second light amount value and step (e-2) for each frequency in the effective range.
The difference data with the minimum value of the light quantity obtained by
(E-4) Using the difference data, the amplitude data of the control signal obtained for each frequency in step (d) is corrected, and (e-5) each frequency corrected in step (e-4). The light beam is scanned while driving the light deflection element based on the amplitude data of each control signal .

Further, a second structure of the present invention is the first structure.
In the scanning beam light amount control method according to the present invention, step (e-5) is performed based on the amplitude data of the control signal for each frequency corrected in (e-5-1) step (e-4). By scanning the light beam within a predetermined range and measuring the light amount of the scanning beam, the third light amount data of the scanning beam is obtained, and (e-5-2) third
While referring to the light amount data of No. 3, while correcting the amplitude data of the control signal within a predetermined range excluding the effective range within the predetermined range regarding frequency, (e-5-3) by step (e-4) The light beam is scanned while driving the optical deflection element based on the corrected amplitude data of the control signal for each frequency and the amplitude data of the control signal corrected in step (e-5-2). It is a thing.

[0019]

In the first configuration of the present invention, the maximum value of the light amount is obtained for each frequency from the first light amount data acquired by measuring the light amount of the scanning beam, and the maximum values of the light amounts are compared. Thus, the minimum value of the maximum value of the light amount is calculated. Further, the amplitude data of the control signal that gives a value obtained by multiplying the minimum value by a predetermined constant value is obtained for each frequency,
The light deflection element is driven based on the obtained amplitude data. At this time, in the first configuration of the present invention,
The light intensity of the scanning beam is further measured based on the measured amplitude data.
Then, the second light amount data is created. Further this second
From the light intensity data of the
The minimum value of the light amount within the range and the first value at each frequency.
The difference data with the light intensity value of 2 is obtained, and this difference data
Is used to correct the amplitude data obtained in the first configuration.
It is. Then, based on this corrected amplitude data, the light
The deflecting element is driven and the deflected beam is scanned. Follow
Then, the light quantity of the scanning beam deflected by the light deflection element is
It becomes a value near the above minimum value, and within the effective range, the light amount is almost
A scanning beam having a constant level is scanned.

[0020]

Further, in the second configuration of the present invention, the amplitude data of the control signal within a predetermined range other than the effective range within the scanning range of the scanning beam is corrected based on the third light amount data. Therefore, the light quantity of the scanning beam at the beginning of scanning the scanning beam within the effective range is kept at a constant level.

[0022]

【Example】

(1) Device Configuration and Schematic Operation FIG. 1 is a diagram schematically showing the electrical and optical configuration of a high-speed drawing device that is an embodiment of the present invention. As shown in the figure, the present apparatus includes an optical system OP, an AOD control board 10 and an EOD.
It is roughly divided into WS (engineering workstation) 20.

Here, the optical system OP is a laser oscillator 1,
The sensor 5 includes an AOD 2, a scanning lens 3, a relay lens system 4, and a photoelectric conversion element. The operation of the AOD 2 is controlled by the control signal V _d generated in the AOD control board 10 as described later.

First, the laser beam L _i oscillated by the laser oscillator 1 is deflected by the AOD 2 according to the control signal V _d . Then, the deflected beam L _d is scanned by the scanning lens 3 when the correction process of the control signal V _d described later is completed.
The light is condensed by the scanning lens 3 and is scanned on the scanning surface PL of the photosensitive material arranged at the image surface position of the scanning lens 3. However, during the correction process of the control signal V _d , the scanning plane PL is
Has been removed from the position shown in FIG.
The deflected beam L _d focused by the relay lens system 4
The light is collected on the light receiving surface of the sensor 5 via. Accordingly, the deflection amount P of the beam L _d is the upper scanning plane PL deflected beam L _d is detected as a light intensity signal V _p which is expressed as a function of scan time for scanning.

On the other hand, the AOD control board 10 includes a VCO 14 for generating a control signal V _d for the AOD 2, an amplifier 15, and an AOD.
The OD driver 16 is provided, and the CPU 11 that controls the VCO 14 and the AOD driver 16 is also provided. Furthermore, the AOD control board 10 applies the frequency control signal V to the data memory 17 for storing the light amount signal V _p , which is the output signal of the sensor 5, as the light amount data, and the VCO 14.
Memory 12 for storing _t (corresponding to control voltage of VCO 14)
And the amplitude control signal V _m to be applied to the AOD driver 16
It also has a memory 13 for storing

C which is the core of the AOD control board 10
The PU 11 has the following functions. That, CPU 11 gives the address control signal V _A to the data memory 17 with reference clock 11a, to a predetermined address in the data memory 17 in response to the address control signal V _A,
The light quantity signal V _p is stored. Then, the CPU 11 reads the light amount signal V _p stored at each address from the data memory 17 at any time, and performs the amplitude control signal V _m according to a correction process described later.
And stores the result in the memory 13. Also, CPU
11 is a frequency control signal V based on the reference clock 11a.
_t is generated and the result is stored in the memory 12. Note that the amplitude control signal V _m a frequency control signal V _t, is synchronized signal.

Further, the CPU 11 reads out the frequency control signal V _t and the amplitude control signal V _m from the memories 12 and 13, respectively, and outputs these signals V _t and V _m to the VCO 14 respectively.
And to the AOD driver 16.

On the other hand, the EWS 20 is connected to the AOD control board 10 via the data bus 30, and various data such as the amplitude control signal V _m and the light quantity signal V _p are transmitted to the EWS 20 through the CPU 11. Then, various data transmitted to the EWS 20 is transferred to the interface (I / F) 21.
After being sent to the CPU 22 of the EWS 20 via a predetermined processing and a predetermined process is performed, the display 2 such as a CRT display
5 is output as a graphic.

A keyboard 23 and a mouse 24 are connected to the CPU 22, and the operator can correct various data displayed on the screen of the display 25 through these input means. Then, the data regarding the corrected amplitude control signal V _m ′ is transferred to the data bus 3
It is sent to the CPU 11 through 0, and the CPU 1
1 stores the corrected amplitude control signal V _m ′ in the memory 13 as a new amplitude control signal. (2) Correction processing of amplitude control signal V _{m As described} above, the deflected beam L scanned on the scanning surface PL
The light intensity of _d fluctuates. Therefore, in order to remove this fluctuation, it is necessary to correct the amplitude of the control signal V _d . Therefore, in the present embodiment, the correction processing of the amplitude control signal V _m is performed based on the following first to third correction methods. Hereinafter, the first to third correction methods will be sequentially described with reference to the flowcharts.

(A) First Correction Method FIG. 2 is a flowchart showing the procedure of the first correction method.

Step SA1 The AOD 2 is actually driven to scan the deflected beam L _d, and data of the light amount signal V _p is created. That is, the amplitude of the control signal V _d is changed for each frequency f (for each scanning position x in the scanning plane PL), and the frequency dependency and the amplitude dependency of the light amount signal V _p are measured. For details, see step SA11.
~ SA17.

First, in step SA11, the initial value f ₁ of the frequency f is set (f = f ₁ ). That is,
A frequency control signal V _t1 that causes the VCO 14 to oscillate a signal of frequency f ₁ is read from the memory 12, and the CPU 11
Applied to the VCO 14. In this embodiment, the frequency f is changed from the initial value f ₁ to the final value f _s with the step width Δf. In practice, the initial value f ₁ is 120MH _z, final value f _s is 70MH _z, step width Δf is 50KH _z.

Next, at step SA12, the initial value of the amplitude control signal V _om (showing the amplitude control signal before correction) is set. In this embodiment, the amplitude control signal V _m (V
_om ) from 0 V to the final value V _{me with a} step width ΔV _m . Practically, the final value V _me is 10 V and the step width ΔV _m is 10/256 V. These data regarding the amplitude control signal _Vom are stored in the memory 13a in advance. From the above, the initial value V _om1 becomes equal to the step width ΔV _m (V _om1 = ΔV _m ).

Next, in step SA13, AOD
The light quantity P ₁ of the deflected beam L _d when 2 is driven by the control signal V _d having the frequency f ₁ and the amplitude V _om1 is measured.

Then, the light quantity signal V _P1 is transferred to the data memory 17
Is stored in

In step SA14, the CPU 11 determines whether the amplitude control voltage V _om is equal to the final value V _me . That is, the amplitude control voltage V _om is increased by the step width ΔV _m until V _om ≧ V _me, and the light quantity P _i of the deflected beam L _d in each amplitude control signal V _om is measured (step SA15).

Next, in step SA16, the CPU 11 determines whether or not the frequency f is equal to the final value f _s . If f> f _s , the frequency f is the final value f _s
The frequency f is reduced by the step width Δf until the value becomes, and the data of the amplitude control signal dependence of the light amount P _i at each frequency f is measured.

Step SA2 If the creation of the light quantity data is completed in step SA1, then the light quantity signal V at each frequency f is calculated from the light quantity data.
Data for the maximum value of _p is created, and a process for _{obtaining the} minimum value P _min from the data for this maximum value is performed. Then, the process of multiplying the minimum value P _min by the constant value α is continuously performed. Of course, these processes are performed by the CPU 11
Done by

Here, FIG. 3 is a diagram showing an example of the light quantity data created in step SA1, in which the horizontal axis represents the amplitude control signal V _om (or V _m ) and the vertical axis represents the light quantity signal V _p.
(Or the amount of light P). Further, in FIG. 3, for the sake of convenience, the curve of the light amount signal V _p corresponding to each frequency f is represented by each coordinate x (x ₁ , x of the scanning position on the scanning plane PL.
₂ …) for each curve. From these curves, it is understood that the light amount signal V _p and the amplitude control signal V _om have a non-linear relationship.

Then, the maximum values (p _m1 , p _m2 ...) _{Are found} for the curve of the light amount signal V _p for each scanning position x shown in FIG. 3 (however, only within the effective range described later), and they are plotted. This is shown in Figure 4. In the figure, the horizontal axis represents the scanning position x, and the vertical axis represents the maximum value P _{max of the} light amount signal V _p.
Is represented. On the abscissa, the range from the scanning position x _o to the scanning position x _e corresponds to a range called an effective range, and FIG. 4 shows the maximum value P _max for the scanning position x within this effective range. The results are shown.

[0041] and the effective range (however, limited to one scanning), the deflected beam L in the scanning range of _d, the deflected beam L quantity up quantity P _i of _d is as varies around the constant level P _i Rise range and the falling range of the light intensity P _i from the constant level until the light intensity P _i becomes 0 (the light intensity P _i
The rise of _i is the delay of AOD2 itself caused by the time required for the ultrasonic wave to propagate from the one end face to the other end face in the acoustic medium in AOD2 after the control signal V _d is applied to AOD2. It is caused by the characteristics. The fall of the light quantity P _i is similar. ) _Is the scanning range of the deflected beam L _d . As schematically shown in FIG. 6, when the photosensitive material 31 is arranged at the position of the scanning surface PL and an image signal or the like is actually recorded on the photosensitive material 31, the effective range 1, that is, the scanning position x The interval between ₀ and the scanning position x _e is one scanning width.

[0042] Then the minimum value P _min of the maximum value P _max is extracted from the data of the maximum value P _max by comparing the value of the maximum value P _max at each scanning position x on each other. In the case of FIG. 4, the maximum value P _{m2 at the} scanning position x ₂
Is the minimum value P _min .

Further, a parameter having a constant value α (0 <α ≦ 1) is introduced here, and the extracted minimum value P _min and constant value α are set.
And is accumulated. That is, the minimum value P _min is the minimum value P
It is corrected to _min ^* (P _min ^* = α · P _min ). Such integration is performed in consideration of the temporal variation of the light amount P,
This is because a slightly lower value P _min ^* is set as the minimum value of the maximum value P _max . Incidentally, a value in the vicinity of 1 is usually used as the constant value α.

Step SA3 Next, at each frequency f, the light quantity signal V _p is the minimum value P.
_An amplitude control signal V _m giving _min ^* is obtained. That is,
In the first correction, the amplitude control signal V _om is corrected so that the light amount signal V _{p at} all scanning positions x within the effective range has the minimum value P _min ^* .
The setting of the minimum value P _min ^* of the maximum value P _{max to} the light amount signal to be the reference for correction is a manifestation of the intention to increase the light amount P of the scanning beam as much as possible. Such correction is performed again based on the light amount data shown in FIG.

Therefore, when the light quantity data of FIG. 3 is overviewed, the minimum value P _{min is} set as the light quantity signal V _p depending on the scanning position x.
There may be two amplitude control voltages V _m that give ^* . For example, at the scanning position x ₁ , the amplitude control signals V _{m at which} the light amount signal V _p has the minimum value P _min ^* are V _m1 and V _m1 ′. Similarly, for the scanning position x _2, there are _two amplitude control signals V _m to be obtained, V _m2 and V _m2 ′. This is a result of the light amount P and the amplitude of the drive signal V _d being non-linear.

Therefore, in this correction, the light amount signal P
_When there are two amplitude control voltages V _m that give _min ^* , the amplitude control signal V exists within the range in which the curve showing the relationship between the light amount signal V _p and the amplitude control signal V _m monotonically increases.
_{Let m} be adopted as the correction value.

According to such a promise, the amplitude control signal V _m which gives the light quantity signal P _min ^* within the effective range is obtained,
FIG. 5 shows the result as a graphic. In the first correction, the amplitude control signal V _m is corrected only within the effective range (x _o ≦ x ≦ x _e ). Therefore, the scanning position is outside the effective range, that is, the rising range (0 ≦ x <x _o ) and the falling range (x _e <x ≦ x _s ) of the light amount P.
For, since the amplitude control signal V _m is not corrected,
The corrected amplitude control signal V _m in the above range shown in FIG. 5 corresponds to the uncorrected amplitude control signal V _om .

Step SA4 Therefore, the amplitude control signal V _m (referred to as a first correction value V _mA ) obtained in the above steps is used as a new amplitude control signal V _m . That is, the first correction value V
_{The mA} is stored in the memory 13 as the amplitude control signal V _m . When actually scanning the photosensitive material 31 with the deflected beam L _d , the first correction value V _mA is read from the memory 13 by the CPU 11 and given to the AOD driver 16. As a result, in principle, the light amount P of the deflected beam L _d deflected by the AOD 2 in the effective range is expected to be always uniform.

(B) Second Correction Method As described above, according to the first correction method, the light quantity signal V _p of the deflected beam L _d is always the minimum value P _min within the effective range.
It is expected to be controlled to be ^* . However, in reality, the light amount signal V _p of the deflected beam L _d is not uniform within the effective range and fluctuates around the minimum value P _min ^* .

Here, FIG. 7 is a diagram showing the light amount signal V _p measured when the AOD 2 is driven using the first correction value V _mA . As shown in the figure, in the range of x _o ≤x≤x _e , there is a slight variation around the minimum value P _min ^* . The variation rate ΔV _p / P _min ^* is about 3% (hereinafter, the variation rate ΔV _p / P _min ^* is referred to as the variation rate ΔV _p / P for convenience.
It will be described as P _min . ). This is due to variations in the characteristics of AOD2 itself and subtle changes in the surrounding environment.
It is considered that this is due to the result of integrating the influence of the slight change in the characteristic of D2 and the slight change in the characteristic of the sensor 5 itself.

Therefore, in the following steps, the first correction value V _mA is further corrected in order to remove the fluctuation amount ΔV _p of the light amount signal V _p . Such a correction is performed by the variation amount ΔV _p (=) of the light amount signal V _p as described below.
V _p −P _min ^* ).

FIG. 8 is a flow chart showing the procedure of the second correction method. Hereinafter, the description will proceed based on FIG.

Step SB1 First, the first correction value V _mA is used as the amplitude control signal V _m for AOD.
2 is driven, and the light amount signal V _p at each frequency f (each scanning position x) is measured. Incidentally, in order to correct the variation of the light quantity signal V _p at the time of measuring the light quantity in the next step SB2, in this step SB1, the measurement is performed several times.

Step SB2 Next, the data of the light quantity signal V _p obtained in step SB1 is smoothed. This smoothing is performed, for example, if the data of the light amount signal V _{p at} the scanning position x is measured n times, n
This is performed by adopting the average value <V _p > of the individual data as the light amount signal V _p at the scanning position x. still,
The data of the light amount signal V _p obtained as a result is shown in FIG.
It corresponds to the one shown in. Further, including the present step SB2, the subsequent steps SB3 to SB7 are all performed by the CPU 1.
1 is performed.

Step SB3 Next, the minimum value P _L of the light amount signal V _p within the effective range is calculated based on the data of the light amount signal V _p obtained in the previous step SB2.

[0056] In the case of the light quantity signal V _p shown in FIG. 7 for example, CPU 11 is light quantity signal V _p in the scanning position x _L
Will be determined as the minimum value P _L.

Step SB4 Furthermore, within the effective range, the light amount signal V _p at each scanning position x (each frequency f) and the minimum value P obtained in the previous step SB3
The difference data ΔP _L and _L is calculated. The distribution shown in FIG. 9 illustrates such difference data ΔP _L.

Step SB5 The difference data ΔP _L calculated in the previous step SB4 is set to AO
A process of shifting in the −x direction is performed in consideration of the delay characteristic of D2. Here, if the delay time in AOD2 is represented by time t _d and the scanning speed of the deflected beam L _d is represented by speed V _s , the shift amount x _{d of the} differential data ΔP _{L in} the −x direction is represented.
Is represented by x _d = V _s · t _d . The delay time t _d of AOD2 is t _d = l _u / V _u , where V _{u is} the sound velocity of the ultrasonic wave propagating in the acoustic medium of AOD2 and l _u is the propagation length of the ultrasonic wave in the acoustic medium. It is calculated by the following relational expression.

FIG. 16 is a diagram showing the difference data ΔP _L ′ after the shift processing is performed.

Step SB6 Finally, the difference data Δ shifted in the previous step SB5
P _L ′ is multiplied by the empirical value β and their value β · (ΔP _L ) ′ is subtracted from the first correction value V _mA .

Then, the new amplitude control signal V _m obtained by the subtraction is stored in the memory 13 as the second correction value V _mB . That is, V _mB = V _mA −β · (ΔP _L ′).

Here, as the value of the empirical value β, for example, when the amplitude control signal V _m is changed in 256 steps within the range of 0V to 10V, the optimum value is about 0.7.
It is obtained by actually measuring the light amount signal V _p by changing the value of the empirical value β.

The amplitude control signal V _mB after the above correction processing is shown in FIG. In the same figure, the first correction value V _mA is also shown for reference. That is, the curve 32 is the first correction value V _mA and the curve 33 is the second correction value V _mB .

Based on such a second correction value V _mB , AO
When D2 is driven and the light amount signal V _p is measured, it is possible to reduce the variation rate ΔV _p / P _min of the light amount signal V _p within the effective range to about 1%.

In this correction method, the first correction value V _mA
And the difference data (ΔP _L ′) can be subtracted from the amplitude control signal V _m which gives the minimum value P _min ^* at each scanning position x within the effective range in the first correction method.
This is because the amplitude control signal V _m within the monotonically increasing range of the V _p -V _m curve of FIG.

If such a process is not performed, the light quantity signal V _p increases conversely even though the first correction value V _mA is reduced by the second correction method, and the light quantity signal is rather increased. should the rate of change ΔV _p / _{P min} of V _p is a problem that increases have occurred. With this, although the relationship between the light amount signal V _p and the amplitude control signal V _m is non-linear as in the conventional technique, it becomes similar to the case where the correction value is calculated by linear approximation. Become.

However, in the present embodiment, since the correction processing is performed in consideration of such non-linearity at the time of the first correction, the above-mentioned adverse effect does not occur.

(C) Third Correction Method Variation rate ΔV _p / of the light quantity signal V _p is calculated by the second correction value V _mB.
Although it became possible to reduce P _min to about 1%, the second correction value V _mB is corrected in order to further reduce the fluctuation rate ΔV _p / P _min .

[0069] That is, in the first and second correction, the correction process of the amplitude control signal V _m in the effective range have been made. As a result, the variation rate ΔV _p / P of the light amount signal V _p
It became possible to suppress _min to about 1%. But,
In order to perform more accurate image recording with this apparatus, it is desired to further reduce the fluctuation rate ΔV _p / P _min of the light amount signal V _p .

Therefore, the current fluctuation rate of about 1% ΔV _p / P
Considering the cause of the occurrence of _min , it can be considered that this variation is mainly due to the overshoot when the light amount rises. This overshoot
It is attributed to the delay characteristic of AOD2 and is phenomenologically interpreted as follows.

That is, even if the control signal V _d is applied to the AOD 2 and the piezoelectric element of the AOD 2 is driven, the amplitude of the ultrasonic wave propagating in the acoustic medium is small for a while, so that the ultrasonic wave diffracts. The light amount P of the deflected beam L _d is AOD
A light amount P commensurate with the power of the control signal V _d applied to
It is considered that it has not become. As a result, in order to rapidly increase the light amount P, it is necessary to further rapidly increase the power of the control signal V _d . After that, since the amplitude of the ultrasonic wave propagating in the acoustic medium corresponds to the power of the control signal V _d applied to the AOD 2, conversely, the light quantity signal V
_It is considered that at the end of the rising time of _p , that is, in the vicinity of the starting point x _{0 of the} effective range, the power of the control signal V _d applied to the AOD 2 exceeds the appropriate value. As a result, in the vicinity of the scanning position x ₀ , the light amount signal V
_Overshoot occurs in _p .

Therefore, based on the above consideration, the third correction is performed. That is, by sequentially correcting only the amplitude control signal V _m within the range of 0 ≦ x ≦ x _o , it is possible to suppress the fluctuation of the light amount signal V _p due to overshoot. However, in this case, it is necessary to prevent the amplitude control signal V _m within the effective range, and thus the second correction value V _{mB, from} being corrected.

Such correction is carried out in the second correction method [V _mA −β · (ΔP _L ′)], and the value of the empirical value β is only within the range of 0 ≦ x ≦ x _o. Is appropriately corrected, and the value of the empirical value β can be realized by performing the above subtraction using the value used in the second correction within the effective range. The correction based on such a technical idea corresponds to the third correction method here.

FIG. 12 is a flow chart showing the procedure in the third correction method. Below, based on this flowchart and FIG. 1, how the above-mentioned empirical value β is corrected will be described in detail.

Step SC1 First, the second correction value V _mB is read by the CPU 11,
It is given to the AOD driver 16. After that, the light quantity P of the deflected beam L _d deflected by the AOD 2 is measured,
The light amount signal V _p is stored in the data memory 17.
Even in this step SC1, the next step SC2
The light amount P is measured several times due to the smoothing at.

Step SC2 Next, the light amount signal V _p is smoothed by the CPU 11, and the smoothed light amount signal V _p is stored in the data memory 17 again. This process is as described in the second correction method.

Step SC3 Next, in the main correction, the smoothed light amount signal V _p and the second correction value V _mB are read from the data memory 17 and the memory 13 by the CPU 11, respectively, and then those data are transferred to the data bus 30. CPU2 in EWS20 via
2 is transmitted.

Then, the CPU 22 processes the data transmitted from the AOD control board 10 in accordance with the operator's command signal input via the keyboard 23 or the mouse 24, and makes the processed data graphic on the screen of the display 25. Will be output. For example, the data regarding the light amount signal V _p is displayed on the screen of the display 25 as shown in FIG. 7, and the data regarding the second correction value V _mB is displayed on the screen of the display 25 as shown in FIG.
Alternatively, it is displayed as shown in FIG.

As a result, the operator can immediately visually recognize the data of the light amount signal V _{p and} the data of the second correction value V _mB . Further, the operator inputs a command signal using the keyboard 23 or the mouse 24 to display the second signal displayed on the screen of the display 25.
The correction value V _mB can be corrected on the screen.

Step SC4 Next, the second correction value V _mB is corrected within the rising range (0 ≦ x <x _o ) of the light amount P. Such a correction is
It is performed by changing the empirical value β at each scanning position within the rising range.

That is, even at each scanning position within the rising range, the second correction value V _mB is V _mB = V _mA −β (ΔP _L ′)
The second correction value V _mB is corrected by changing the empirical value β for each scanning position. Therefore, the empirical value β is expressed as a function of the scanning position x, and the empirical value β ′ after such correction is hereafter referred to as the empirical value β ′.
It will be described as (x). Further, the corrected second correction value V _mB will be simply described as the amplitude control signal V _m hereinafter. Therefore, the amplitude control signal V _m in this correction is an amount represented by V _m = V _mA −β ′ (x) (ΔP _L ′).

Therefore, the operator refers to the data of the amplitude control signal V _m displayed on the screen of the display 25, and the CPU 2 through the keyboard 23 or the mouse 24.
Input data on the empirical value β ′ (x) (0 ≦ x <x _o ) into 2. Upon receiving these data, the CPU 22 immediately calculates a new amplitude control signal V _m by the above-mentioned formula, and again displays the data of the new amplitude control signal V _m on the screen of the display 25.

FIG. 13 shows an example of the amplitude control voltage V _m after such correction, and for convenience, the display 25
The rising range (0 ≤ 0
x <x _o ) and a part of the effective range (x _o ≦ x ≦ x _e ) are shown. In the figure, a solid line 34
Indicates the second correction value V _mB , and the broken lines 35 to 37 indicate simulation results obtained by variously changing the empirical value β ′ (x) within the rising range.

Incidentally, based on the phenomenological consideration of the cause of the above-mentioned overshoot, the curved line representing the corrected amplitude control signal V _m has a curve like the broken line 35 in FIG. Is the absolute value of the slope of the curve | d
V _m / dx | is large, rising at the end (x _o vicinity) is the absolute value of the slope | is where it is small curve is optimally be readily understood | dV _m / dx. Therefore, the operator must use the empirical value β '(x) to obtain such a curve shape.
Will be corrected by thinking and error. However, as the operator repeats such correction, the optimum empirical value β ′ (x)
Will be able to determine quickly.

Step SC5 The amplitude control signal V _m corrected in the previous step SC4
The data of the amplitude control signal V _m ′ (hereinafter referred to as “amplitude control signal V _m ”) is sent from the CPU 22 via the data bus 30 to the CPU 11.
Then, the new amplitude control signal V _m is stored in the memory 13. Then, the light quantity P of the deflected beam L _d at each frequency f is measured again based on the new amplitude control signal V _m ′.

The light quantity signal V _p ′, which is the measurement result, is read from the data memory 17 by the CPU 11, transmitted again to the CPU 22 via the data bus 30, and then graphic-outputted on the screen of the display 25.

[0087] Step SC6 Meanwhile, CPU 22 is 'on the basis of the data concerning the light amount signal V _p of the effective range' new intensity signal V _p which has been transmitted rate of change _{ΔV p '/ P min = (} V p' -
P _min ) / P _min , and the variation rate (ΔV _p ′) / P
_Judge whether the maximum value of _min is within the allowable range.

The allowable range referred to here is the variation rate (Δ
V _p ′) / P _min is within 0.8%. The fluctuation rate within 0.8% means that the sensitivity of the sensor 5 is 256.
Considering the level, it is an amount that is considered to correspond to the noise amount at the time of measuring the light amount. According to this correction method, the fluctuation rate (ΔV _p ′) / of the light quantity signal V _p ′ /
It is possible to actually reduce P _min to around 0.8%.

If the variation rate ΔV _p ′ / of the light quantity signal V _p ′ is
If P _min is greater than 0.8%, step SC4 again.
Returning to, the series of correction processes described above will be performed.

[0090] On the other hand, the light quantity signal V _p 'rate of change [Delta] V _p' /
If P _min is within the allowable range, this correction process ends, and the amplitude control signal V _m ′ at the present time is again transmitted to the CPU 11 via the data bus 30 as the third correction value V _mc and stored in the memory 13. .

Then, in the subsequent scanning of the deflected beam L _d , the third correction value V _mc and the frequency control signal V
The light quantity of the deflected beam L _d is controlled based on _t .

In the third correction described above, the amplitude control signal V _m in the same range is corrected by appropriately correcting the empirical value β only within the range of the scanning position 0 ≦ x ≦ x _0. Although the embodiment has been described, the scanning position 0 ≦ x ≦
Needless to say, the overshoot can be corrected by directly modifying the amplitude control signal V _m only within the range of x ₀ .

Although the first to third corrections have been described above, these corrections can be carried out online by using the apparatus shown in FIG. 1. Therefore, the light quantity correction work is simplified, and as a result, the light quantity correction work is performed. It is possible to reduce the time and labor required for

[0094]

As described above, according to the invention of claim 1, the optimum control signal amplitude data for measuring the light quantity of the scanning beam and controlling the light quantity of the scanning beam can be calculated easily and quickly. There is an effect that can be.

Further, according to the present invention, the light quantity of the scanning beam deflected by the light deflecting element is kept at the maximum light quantity obtained from the light beam incident on the light deflecting element, and the fluctuation of the light quantity of the scanning beam within the effective range is suppressed. It also has the effect of being able to.

[0096] Further, the present invention also has an advantage of being able to also respond flexibly to fluctuations in characteristics such as change and elements of the environment, to reduce the change of light intensity run査beam.

[0097] Also, according to the second aspect of the invention, claim
The fluctuation of the light quantity of the scanning beam can be further reduced as compared with the case of the invention described in the first aspect . Specifically, it is possible to reduce the fluctuation of the light quantity to the same level as the noise quantity at the time of measuring the light quantity.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing the configuration of a high-speed drawing apparatus that is an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure of a first correction method.

FIG. 3 is an explanatory diagram showing light amount data.

FIG. 4 is an explanatory diagram showing a maximum value of a light amount signal at each scanning position.

FIG. 5 is an explanatory diagram showing an amplitude control signal.

FIG. 6 is an explanatory diagram showing a relationship between a photosensitive film and an effective range.

FIG. 7 is an explanatory diagram showing a light amount signal measured after the first correction process.

FIG. 8 is a flowchart showing a second correction method.

FIG. 9 is an explanatory diagram showing difference data.

FIG. 10 is an explanatory diagram showing shifted difference data.

FIG. 11 is an explanatory diagram showing an amplitude control signal that has been subjected to a second correction process.

FIG. 12 is a flowchart showing a procedure of a third correction method.

FIG. 13 is an explanatory diagram showing an amplitude control signal that has been subjected to third correction processing.

FIG. 14 is a diagram showing an electrical configuration of a conventional technique.

FIG. 15 is a diagram showing power of a drive signal.

FIG. 16 is an explanatory diagram showing the maximum deflection efficiency obtained by measuring the amount of light.

FIG. 17 is an explanatory diagram showing an example of a drive signal.

[Explanation of symbols]

OP optical system P light quantity L _d deflected beam PL scanning surface V _p light quantity signal V _d control signal V _m amplitude control signal V _t frequency control signal 1 laser oscillator 2 AOD 5 sensor 10 AOD control board 11 CPU 12 memory 13 memory 14 VCO 16 AOD driver 20 EWS 22 CPU 23 Keyboard 24 Mouse 25 Display 30 Data bus 31 Photosensitive material

Claims (2)

(57) [Claims] 1. A method of controlling the light quantity of a scanning beam when scanning the light beam using an optical deflection element which deflects the light beam according to a control signal and changes the deflection angle, comprising: ) Measuring the light quantity of the scanning beam by changing the frequency and amplitude of the control signal within a predetermined range, and obtaining first light quantity data of the scanning beam; and (b) from the first light quantity data, Determining a maximum value of the light quantity of the scanning beam for each frequency of the control signal within a range defined in advance as an effective range within the predetermined range regarding the frequency; and (c) each of the frequencies. Of the maximum value of the light amount obtained with respect to the value, obtain the minimum light amount value, and multiply the minimum value by a predetermined constant value to correct the minimum value, (d) the effective range Within For each frequency of the control signal, the amplitude of the control signal that gives the corrected minimum value obtained in step (c) is calculated from the first light amount data obtained in step (b). And a step of (e) scanning the light beam while driving the optical deflection element based on the amplitude data of the control signal for each of the frequencies obtained in step (d) , The step (e) includes: (e-1) the step obtained in the step (d).
Based on the amplitude data of the control signal for each frequency
Scan the light beam and measure the light intensity of the scanning beam
To obtain the second light quantity data of the scanning beam.
And (e-2) the effective range from the second light amount data.
Determining a minimum value of the light amount within the range (e-3), for each frequency within the effective range,
The light intensity value of 2 and the value obtained by the step (e-2)
Obtaining difference data with the minimum value of the light quantity; (e-4) using the difference data, the step
(D) of the control signal obtained for each frequency
A step of correcting the amplitude data, and (e-5) a step of correcting the amplitude data by the step (e-4).
Based on the amplitude data of the control signal for each frequency
Scan the light beam while driving the light deflection element.
And a step of controlling the light quantity of the scanning beam. 2. A light quantity control method for a scanning beam according to claim 1.
In the method, step (e-5) is corrected by (e-5-1) step (e-4).
Based on the amplitude data of the control signal for each frequency
Within the predetermined range for the frequency.
Scanning the beam and measuring the light intensity of the scanning beam.
To obtain the third light amount data of the scanning beam.
Step (e-5-2) Referring to the third light amount data,
Within the predetermined range for the frequency, the effective range
Modify the amplitude data of the control signal within the range excluding
Correcting step, (e-5-3) Corrected by the step (e-4)
And the amplitude data of the control signal for each frequency
The control signal corrected in step (e-5-2)
Drive the optical deflection element based on the amplitude data of
One, the light quantity control method of the scanning beam, characterized in that it comprises the steps of: scanning the light beam.