JPH10170849A - Control method for inner surface scan type optical beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To linearize a scanning line with a simple control when plural pieces of light beams are used, to make the scanning line interval easily changeable, and to simplify the constitution, by controlling so as to tilt the light beams in the right angle direction to a plane containing a rotary shaft by an angle decided by an operation result from a tilt angle and a rotational angle of a spinner. SOLUTION: An oblique incident beam is tilted respectively by θx, θy in the x, y directions. The slope θy is obtained by an AOM control part 40, and a driven signal having a frequency for generating this slope θy is applied to one side transducer of an AOM2. The θx is operated in a θx operation part 42. This operation is performed using a spinner rotational angle ψand the θy. The θx being this operational result is inputted to the AOM control part 44, and the frequency for generating the slope θx is obtained in it. Thus, since the oblique incident beam may be tilted by the angle θx being the function of the spinner rotational angle ψ to the other side while tilting by a fixed angle θy to one side, the control is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an inner-surface scanning light beam scanning apparatus that combines a plurality of light beams and scans the inner surface of a cylindrical drum with a common scanning optical system.

[0002]

2. Description of the Related Art There is known an inner surface scanning type light beam scanning device which scans by guiding a light beam such as a laser beam to the inner surface of a cylindrical drum. In order to increase the recording speed in this apparatus, a method of using a plurality of light beams, that is, a multi-beam method has been proposed.

In an inner surface scanning type apparatus, a plurality of light beams introduced along a central axis of a cylindrical drum are rotated by a reflecting mirror (spinner) which rotates at a high angle of 45 ° with respect to the central axis. Guide to the inside. However, in this case, when the positions of the plurality of light beams are fixed and guided to the spinner, the relative positions of the light beams periodically change as the rotation angle of the spinner changes. For this reason, a plurality of scanning lines recorded on the recording drum periodically bend and intersect with each other, so that correct scanning cannot be performed.

Therefore, one of the plurality of light beams is positioned on the center axis of the scanning optical system (on the center axis of the recording drum) as a reference beam, and the other light beams are synchronized with the rotation of the spinner. Has been considered to be swiveled about this reference beam. In this case, by changing the phase of the spinner and the other light beams, the curvature of the scanning line can be eliminated to make the scanning line straight. Also, by changing the distance between the reference beam and another light beam, the distance between the scanning lines can be changed.

For example, JP-A-5-27188, JP-A-5-27188
No. 276335 discloses a method of rotating a deflection element (such as a prism) having a fixed deflection amount in synchronization with the rotation of a spinner. U.S. Pat.
No. 1, US Pat. No. 5,502,709 proposes a method of two-dimensionally deflecting a light beam other than the reference beam.

[0006]

2. Description of the Prior Art The former method of rotating a deflection element having a fixed deflection amount has a problem that the beam interval cannot be changed because the deflection amount is constant, and therefore the scanning line interval cannot be changed. there were. Although it is desirable to change the interval between scanning lines depending on the recording density, this conventional technique has a disadvantage that the scanning line density cannot be changed corresponding to the recording density. In order to stably rotate the deflecting element in synchronization with the spinner that rotates at high speed, a high-precision mechanical rotation transmission mechanism is required, but such a mechanism is difficult to obtain or expensive. .

In the latter method of two-dimensionally deflecting a light beam, a plurality of piezo mirrors and acousto-optical elements (Acoust
It is necessary to combine an o-optic modulator (hereinafter, referred to as AOM) to perform a complicated two-dimensional deflection in two orthogonal directions (x, Y directions) while maintaining a fixed relation to each other. For this reason, control was complicated, it was difficult to stabilize quality, and it was expensive.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and when a plurality of light beams are used, the scanning lines can be straightened by simple control and the scanning line interval can be easily changed. An object of the present invention is to propose a control method of an inner surface scanning type light beam scanning device which can be simplified.

[0009]

According to the present invention, an object of the present invention is to provide a control method of an inner surface scanning type light beam scanning apparatus for combining a plurality of light beams and scanning the inner surface of a cylindrical drum by a spinner.
One light beam is incident on the spinner along the central axis common to the spinner and the cylindrical drum, and the other light beam is fixed at a predetermined angle for each light beam separately in a plane including the central axis. an inner surface scanning type light beam that is controlled so as to be tilted in the direction orthogonal to the plane including the rotation axis by an angle θx determined by a predetermined arithmetic expression based on the tilt angle θy and the rotation angle の of the spinner. Control method of the scanning device.

As will be described later, an arithmetic expression for determining θx is as follows: when 0, θx = θy (1-cosψ) / sinψ)
When ψ = 0, θx = 0. As described above, since the inclination θy in the y direction is a fixed value, only the inclination θx in the X direction needs to be calculated. Therefore, the configuration of the arithmetic circuit is particularly simplified.

The distance d between the scanning lines is given by d = f · f where f is the focal length of the focusing lens (condensing lens).
θy, the desired interval d
Can be determined by θy = d / f. Therefore, the setting is very simple.

The number of light beams may be three or more.
In this case, one (reference beam) is placed on the center axis of the spinner, the second light beam is inclined in the y direction at θy = d / f, and the third and subsequent light beams are set to −θy, 2θy, −2θ.
y, 3θy,... Note that the inclination θx in the X direction of each light beam is the inclination θ in the respective Y directions.
Of course, the calculation is performed using y, −θy, 2θy, −2θy, 3θy,.

According to this method, a time shift in the main scanning direction, that is, a scan phase shift occurs in the other light beams with respect to the basic beam. This phase shift can be eliminated by correcting the clock timing of the image signal. This calculation will be described later.

[0014]

[Principle] FIG. 4 is a view for explaining the principle, and FIG. 5 is a view showing scanning lines drawn on the inner surface of the cylindrical drum D. L ₀ is the reference beam, L ₁ is the other light beam. These light beams L ₀ ,
L ₁ passes through a focusing lens (not shown), is reflected in the radial direction of the drum D by a spinner rotating on the center axis CL of the drum D, and forms an image on the inner surface of the drum D.

The rotation angle of the drum D is indicated by ψ. The reference beam L ₀ is incident along the center axis CL of the drum D,
Draw scan line or reference scan line SL ₀ of the straight line as shown in FIG. 5 on the inner surface of the drum D. Other beam L ₁ is ψ
= Tilt small angle θy in the direction of the [psi ₀ shall be incident on the spinner. Thus the light beam L ₁ is the fact that obliquely incident beam.

This oblique incident beam L ₁ draws a curved scanning line SL ₁ as shown in FIG. 5, and the spinner makes ψ = ψ ₀
Farthest from the reference scan line SL ₀ when the. The distance d is d = f · θy. Here, f is the focal length of the focusing lens.

The coordinate x on the drum D, it is determined as shown in FIG. 5 a y, scan lines SL ₁ by the oblique incidence beam L ₁ is
It can be expressed by the following equation. x = f · θy · sin (ψ−ψ ₀ ) y = f · θy · cos (ψ−ψ ₀ )

[0018] The incident direction of the oblique incidence beam L ₁ in this state, it is assumed that the tilting only θx in the direction perpendicular to the direction of inclination of [theta] y. Scan line SL ₁ of the oblique incidence beam L ₁ at this time can be expressed by the following equation. x = f · θy · sin ( ψ-ψ 0) -f · θx · cos (ψ-ψ 0) ... (a) y = f · θy · cos (ψ-ψ 0) + f · θx · sin (ψ- ψ ₀ )… (b)

Here, θy is a constant, and θx changes in synchronization with the rotation angle の of the spinner and is a function of the angle ψ.

In order for the scanning line SL ₁ to be a straight line and the interval from the reference scanning line SL ₀ to be a constant value d, y in the equation (b) obtained above must be a constant value d = f · θy. is necessary. That is, f · θy = f · θy · cos (ψ−ψ ₀ ) + f · θx · sin (ψ−ψ ₀ ) θy (1−cos (ψ−ψ ₀ )) = θx · sin (ψ−ψ ₀ ) ∴θx = θy (1-cos ( ψ-ψ 0)) / sin (ψ-ψ 0) ... (c): However the ψ ≠ ψ _0. It should be noted that the θx = 0 at the time of ψ = ψ _0.

From the above description, θy is set to the scanning line S
Θy = θy so that the interval d between L ₀ and SL ₁ is a predetermined interval d _0.
After determining by d ₀ / f, if θx is changed along with the rotation of the spinner according to the above equation (c), it can be understood that the scanning lines SL ₀ and SL ₁ formed by straight lines at the interval d ₀ can be obtained.

[0022] Note that in this case, the scan line SL ₁ is the phase of the reference scan line SL ₀ and X direction (main scanning direction) is changed. This variation can be obtained by the following equation. That is, the following equation is obtained by substituting θx obtained by equation (c) into equation (a). θx = f · θy · sin ( ψ-ψ 0) -f · θy · cos (ψ-ψ 0) (1-cos (ψ -ψ 0)) / sin (ψ-ψ 0) ... (d) thus scanning a synchronization signal line SL ₁ may be corrected by formula (d).

As described above, according to the present invention, when the scanning line interval is set to d, the inclination (deflection angle) θy in the y direction is set to a constant value of d / f, and the inclination (deflection angle) in the X direction is set. θx
Is calculated by equation (c) and scanning is performed, so that the control is simple.

Further, since θy may be a fixed value, the deflection in this direction may be performed by, for example, mechanically moving a mirror and setting the angle in advance, so that an AO element or a piezo mirror for changing at a high speed can be used. Becomes unnecessary, and an inexpensive configuration can be realized. Here, the calculation of θx may be performed in real time (real time) while scanning, but the calculation result may be stored in memory and scanning may be performed while reading this result.

[0025]

FIG. 1 is a conceptual diagram showing an embodiment of the present invention partially omitted, and FIG. 2 is a block diagram of a control system thereof.

In FIGS. 1 and 2, reference numerals 10 and 12 denote laser diodes. These laser diodes 10, 1
2 emits linearly polarized light beams (laser beams) L ₀ and L ₁ , these are arranged so that their polarization directions are orthogonal to each other, and the two light beams L ₀ and L ₁ are collimated by the collimating lenses 14 and 16. After the collimated beam by the acousto-optic element AO
The light is guided to the polarization beam splitter 18 via M1 and AOM2, where it is multiplexed. Note that one light beam L
_{When 0} is used as the reference beam, AOM1 can be omitted.

The beam diameter of the combined light beam L ₂ is further expanded and changed in the lenses 22 and 24 constituting the beam expander 20. This beam L
₂ is the drum 2 along the center axis CL of the drum (cylindrical) 26.
It is led into 6.

On a central axis CL of the drum 26, a focusing lens (condensing lens) 28 forming a scanning optical system is provided.
And a spinner 30. This spinner 3
Numeral 0 has a reflection surface of approximately 45 ° with respect to the central axis (rotation axis) and is rotated at high speed by a motor. Note that a rotary encoder 32 as an angle detecting means is attached to this motor, and the rotation angle (ψ = ωt) of the spinner 30 is detected. The beam guided to the spinner 30 passes through the beam expander 20 and the focusing lens 28 on the rotation axis, and focuses on the inner peripheral surface of the drum 26 or the recording sheet 34.

The beam expander 20 is provided with a beam splitter 36. The beam splitter 36 is led to the multiplexing beam L 4 divided position detecting device 38 by dividing a part of _2, the beam position of the light beam L _0, L ₁ is detected. The beam splitter 36 and the divided position detecting element 38 form a beam position detecting means.

AOM1 and AOM2 are driven by ultrasonic waves generated by the transducer, and diffract an incident beam by a standing wave generated by the ultrasonic waves. The first-order diffracted light at this time is selected by a zero-order light cut plate (not shown). By changing the frequency of the ultrasonic drive signal, the angles of the light beams L ₀ and L ₁ change.

AOM1 and AOM2 can be deflected two-dimensionally. That is, it has two sets of transducers in directions orthogonal to each other and can deflect independently in both directions. Note here one of the light beam L ₀ as the reference beam shall be positioned on the center axis CL of the drum 26 and the spinner 30.

If the reference beam L ₀ can be accurately positioned on the central axis CL, the AOM 1 is unnecessary. If this is difficult, the beam position of the reference beam L ₀ is detected by the beam position detecting element 38, and the correction data by the AOM 1 is stored in memory, and the reference beam L ₀ is correctly corrected during scanning.
Align to L.

[0033] AOM2, as described in the principle, each oblique incident beam L ₁ x, the y-direction [theta] x, tilting [theta] y. The inclination θy is obtained by the AOM control unit 40, and a drive signal having a frequency for generating the inclination θy is applied to one transducer of the AOM2.
Here, θy is a fixed value determined by the scanning line interval d and the focal length f of the focusing lens 28 as described above.

Θx is calculated by the θx calculation unit 42. This calculation is performed according to the above equation (c) using the spinner rotation angles ψ and θy. The resulting θx is A
The frequency is input to the OM control unit 44, and a frequency for generating a gradient of θx is obtained here. The drive signal of this frequency is AO
M2 is applied to the other transducer. This θx
May be performed in real time during scanning, or the result of the calculation may be stored in memory and data may be read from this memory during scanning.

It should be noted the beam position of the oblique incident beam L ₁ is detected by the beam position detecting device 38, is fed back to the detected beam position to the AOM control part 42 or 40, so as to match the beam position in θx or θy It is better to correct. This correction may be performed in real time while scanning, or preliminary scanning may be performed and data for this correction may be stored in advance.

The laser diodes 10 and 12 are controlled by a light source controller 46. The light source controller 46 is the spinner 3
Based on the clock timing synchronized with the rotation angle の of 0, the laser diodes 10, 1
Turn 2 on / off. Laser diode 10 for emitting the reference beam L ₀ here is turned on and off at a clock timing synchronized to the rotation angle [psi. However laser diode 12 for emitting the oblique incident beam L ₁ is on the clock timing is corrected according to the equation (d)
Turned off.

[0037]

FIG. 3 is a diagram showing another embodiment.
In this figure, reference numeral 50 denotes a laser light source such as helium / neon or argon. The laser light source 50 a single laser beam L ₀₀ emitted from a P-polarized light by the polarizing beam splitter 52 (the plane of vibration of the electric field, polarization parallel to the incident plane including the incident light reflected light), S Polarization (polarization in which the vibration plane of the electric field is perpendicular to the plane of incidence). The P-polarized light beam is the reference beam L ₀ and is incident on the AOM 1 via the lens group.

The S-polarized light beam L ₁ split by the beam splitter 52 is incident on the AOM 2 via the mirror 54 and the lens group. The two light beams L ₀ and L ₁ are each expanded by a lens group and then combined by a mirror 56 and a polarizing beam splitter 58. In FIG. 3, FIG.
Since the same reference numerals are given to the same portions as 2, the description will not be repeated.

In the present invention, a movable mirror can be used instead of the AOM. As the movable mirror to be used, a piezo mirror using a piezo element, a galvanometer mirror using a galvanometer, or the like can be used. In the embodiment described above, the spinner 30 uses a mirror that rotates at an angle of 45 ° with respect to the central axis C of the drum 26. However, instead of the mirror, the diffraction grating is rotated to rotate the central axis CL.
A light beam (laser beam) guided along the line may be guided to the inner surface of the drum.

[0040]

According to the first aspect of the present invention, one light beam is incident on the central axis of the spinner as a reference beam, and the other obliquely incident beam is at a constant angle θy in a plane including the central axis.
At the same time, the angle θx is determined in a direction perpendicular to this plane by an angle θx determined by a predetermined arithmetic expression based on the spinner rotation angles ψ and θy.

For this reason, the obliquely incident beam need only be inclined to one side at a fixed angle θy and only to the other side at an angle θx which is a function of the spinner rotation angle ψ, so that the control is simplified. Here, not only θx can be obtained by the equation (c), but also the movable mechanism of θy can be configured at low cost. (Claim 2). Further, the fixed angle θy can be obtained from the scanning line interval d and the focal length f of the focusing lens, and it is easy to change the interval d.

The present invention can use three or more light beams. In this case, θy of the oblique incident beam is set to d / f
, -1 times, 2 times, -2 times, 3 times,... (Claim 4). Further, according to the present invention, it is inevitable that each scanning line is shifted in time in the scanning direction.
Therefore, the clock timing of each light beam may be corrected based on the rotation angle of the spinner.

[Brief description of the drawings]

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

FIG. 2 is a control block diagram thereof.

FIG. 3 is a conceptual diagram of another embodiment.

FIG. 4 is an explanatory diagram of a principle.

FIG. 5 is a diagram illustrating a scanning line.

[Explanation of symbols]

10, 12 Laser light source 20 Beam expander D, 26 Cylindrical drum 28 Focusing lens 30 Spinner 40, 44 AOM control unit 42 θx calculation unit 46 Light source control unit L ₀ , L ₁ light beam L ₂ combined light beam CL Central axis AOM 1, AOM2 acousto-optic device

Claims (5)

[Claims] 1. A control method for an inner surface scanning type light beam scanning apparatus which combines a plurality of light beams and scans an inner surface of a cylindrical drum by a spinner, wherein one light beam is shared by a central axis of the spinner and the cylindrical drum. Incident on the spinner along, and tilt other light beams in a plane including the central axis by a predetermined angle θy separately determined for each light beam in advance, and by using the tilt angle θy and the rotation angle の of the spinner, A control method for an inner surface scanning type light beam scanning device, characterized in that control is performed so as to incline in a direction perpendicular to the plane including the rotation axis by an angle θx determined by a predetermined arithmetic expression. 2. The predetermined arithmetic expression is: θx = θy when ψ ≠ 0
2. The method according to claim 1, wherein (1−cos の) / sinψ, and θψ = 0 when ψ = 0. 3. The distance d between scanning lines drawn by a plurality of light beams and the focal length f of a focusing lens are denoted by d.
3. The control method for an inner surface scanning type light beam scanning device according to claim 1, wherein the inclination angle θy is set so that = f · θy. 4. Scanning with three or more light beams, placing one of them on the central axis, and setting the inclination angle θy in a plane including the central axis of the other light beams to an integral multiple of d / f. Claim 1
3. The method for controlling an inner surface scanning type light beam scanning device according to any one of items 1 to 3. 5. The inner surface scanning according to claim 1, wherein a time shift of a scanning line drawn by a plurality of light beams to a main scanning method is corrected by synchronizing a clock timing of an image signal with a rotation angle ψ of a spinner. Control method of a scanning type light beam scanning device.