JPH0685036B2 - Deflection-type optical beam scanning method - Google Patents

Description

The present invention relates to a deflection type light beam scanning method used in a field requiring constant velocity light beam scanning.

"Prior Art" Optical scanners such as laser printers and copiers that require constant-speed light beam scanning employ a method of deflecting a light beam as a scanning means at this time.
The deflection type light beam scanning method illustrated in the figure is adopted.

The method shown in FIG. 3 will be briefly described below. 1 is an acousto-optic device of bulk type or thin film laminated type, 2 is a sound wave drive circuit connected to the acousto-optic device 1, and 3 is a sound wave drive circuit 2. Sawtooth wave generation circuit, 4 is acousto-optic element 1
An image forming lens (fθ lens) arranged on the emission side of 5 is a blocking body for blocking the straight non-deflected light, 6 is a photoconductor (light receiving body) arranged at the focal position of the image forming lens 4, Reference numeral 7 denotes an image plane of the photoconductor 6.

In FIG. 3, the light beam L ₁ incident on the acousto-optic element 1 from a light source (not shown) is deflected by Bragg diffraction through the sound wave drive circuit 2, and the deflection angle is increased by the imaging lens 4. Then, this becomes a light beam L ₂ and an image is formed on the image forming surface 7 of the photoconductor 6.

The light deflection angle Δθ at this time is proportional to the change Δf _S of the sound wave frequency as shown in the equation (1).

Δθ = λ / v _S · Δf _S (1) λ: Light wavelength in acousto-optic element (medium) v _S : Sound wave propagation speed Therefore, sawtooth wave generation circuit 3 connected to sound wave drive circuit 2 When the frequency of the driving sound wave to the acousto-optic element 1 is swept by the change of the input control voltage of, the optical deflection angle Δθ changes, and the light beam scanning is performed on the image plane 7.

Next, the scanning movement of the optical imaging spot in the method of FIG. 3 will be considered.

When the light deflection angle of the acousto-optic element 1 is Δθ, the position y of the image spot of the light beam on the image plane 7 is represented by the equation (2).

y = f ₀ tan Δθ (2) y: distance from the image forming spot to the optical axis f ₀ : focal length of the image forming lens The scanning speed of the light beam at the image forming spot is the sawtooth of the acoustooptic device 1. Since it is driven by a circular wave, it becomes as shown in equation (3).

dy / dt = f ₀ sec ² Δθ · d Δθ / dt (3) As is apparent from the equation (3), the scanning speed is a function of the light deflection angle Δθ and changes non-linearly. Therefore, the light deflection angle Δθ increases at a position where it increases.

Therefore, the light beam (scanning line) has a larger light deflection angle Δθ from the central portion of the image forming surface 7 toward the upper end portion and the lower end portion thereof, and presents a non-constant speed scanning situation.

Therefore, the distance between the imaging spots in the scanning direction of the light beam also increases from the center of the imaging surface 7 toward both upper and lower ends thereof.

In the method shown in FIG. 3, an imaging lens 4 such as an fθ lens is used to perform the uniform velocity scanning movement of the light beam, and the position y of the imaging spot is replaced by the following equation (4).

y = f ₀ · Δθ (4) In the light beam scanning in this case, since the acoustooptic device 1 is driven by the sawtooth wave, dΔθ / dt: becomes constant, and therefore the constant velocity scanning motion is It becomes like the formula (5).

dy / dt = f ₀ · dΔθ / dt = f ₀ A (5) A: constant “Problems to be solved by the invention” In the third method described above, for example, a bulk-type acousto-optic device is used. When it is used, a special lens such as an fθ lens or a combination of a plurality of lenses is required in order to perform constant velocity scanning of the light beam, and the lens design and manufacture are complicated.

On the other hand, when a thin film laminated acousto-optic device is used in the above method, the acousto-optic device, ordinary thin film lenses (mode index lens, geodesic lens, diffractive lens) and the like can be easily integrated on the same substrate. When a special lens such as an fθ lens is required, it is difficult to reduce the thickness of the special lens, which hinders downsizing, weight reduction, and integration of the device, and also requires adjustment of the optical system.

In view of the above problems, the present invention makes it possible to easily carry out uniform speed scanning of a light beam by a deflecting means, and further, downsizing, weight saving, and integration of the device can be achieved without adjusting the optical system. The present invention aims to provide a highly reliable deflection type light beam scanning method.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes an acousto-optical element, a sound wave drive circuit for the acousto-optical element, and a voltage control circuit as a deflection scanning means for a light beam. A deflection type light beam that is provided with an image forming optical system as an image forming means for forming an image of a light beam that has passed through an optical element on the image forming surface and scans the image surface while deflecting the light beam through these means. In the scanning method, when the acousto-optic element is driven through the sound wave drive circuit, the frequency sweep waveform of the sound wave output is controlled by the voltage control circuit to scan the light beam at a constant speed on the imaging surface. .

[Examples] Hereinafter, specific examples of the method of the present invention will be described with reference to the drawings.

In FIG. 1, 11 is a light source and 12 is an acousto-optic device.

The acousto-optic device 12 includes an acousto-optic element 13 and an imaging optical system 14
And a shield 15 are assembled on a substrate, the acousto-optic element 13 is a bulk type or a thin film laminated type, and the imaging optical system 14 is a normal lens or a combination of thin film type lenses. .

Reference numeral 16 is a sound wave drive circuit, 17 is a voltage control circuit, and the voltage control circuit 17 comprises a voltage correction circuit section 18 and an arctangent wave generation circuit section 19 which are mutually connected.

The sound wave drive circuit 16 is connected to the acousto-optic element 13, and the voltage control circuit 17 is mutually connected to the sound wave drive circuit 16 via the voltage correction circuit section 18.

Reference numeral 20 denotes a photoconductor (or a photoconductor) arranged at the focal position of the imaging optical system 14, and 21 denotes an image formation surface of the photoconductor 20.

In the case of the above-described method of the present invention, the light beam L ₁ such as a laser beam emitted from the light source 11 is incident on the acousto-optic element 13 to be deflected, and the deflection angle is increased by the imaging optical system 14, The light beam L ₂ is imaged on the imaging surface 21 of the photoconductor 20.

At this time, the acousto-optic element 13 is driven through the sound wave drive circuit 16, and the sound wave drive circuit 16 is controlled by the voltage control circuit 17 including the voltage correction circuit unit 18 and the arctangent wave generation circuit unit 19. It

That is, the frequency-swept waveform of the sound wave output of the acousto-optic element 13 becomes arctangent by the arctangent wave generation circuit unit 19, and the relationship between the sound wave frequency f _S and the input control voltage v is obtained via the voltage correction circuit unit 18. Since it is controlled accurately, the light beam L ₂ exhibits a highly accurate uniform velocity scanning motion on the image plane 21.

In the method of the present invention, sec ² in the above-mentioned equation (3) is used.
Make Δθ constant.

In this case, the deflection angle Δθ is expressed as in equation (6),
The scanning waveform generating circuit is designed to satisfy (7).

△ θ ＝ tan ^-1 (At) …… (6) △ f _S ＝ v _S / λ ・ △ θ ＝ v _S / λ tan ^-1 (At) …… (7) v _S : speed of sound, λ: light Wavelength A: constant, t: time Thus, the light beam can be scanned at a constant speed at the image forming spot.

FIG. 2 shows the scanning waveform of the sound wave frequency change in the method of the present invention and the scanning waveform of the sound wave frequency change in the conventional example (FIG. 3). The dotted line is the conventional example.

When the linearity of the modulation element is guaranteed in the method of the present invention, the voltage control circuit 17 may be composed of only the arctangent wave generation circuit section 19.

[Advantages of the Invention] As described above, according to the method of the present invention, the uniform velocity scanning of the light beam on the imaging plane can be easily performed by electrically controlling the driving sound wave frequency of the acousto-optic element. Regardless of whether a bulk type or a thin film laminated type is used as the acousto-optic element, it is easy to design and manufacture a lens for an imaging optical system combined with it, and it is of course unnecessary to adjust the optical system. The device for carrying out the present invention is compact, lightweight, integrated, and highly reliable.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing an embodiment of the method of the present invention, and FIG.
FIG. 3 is an explanatory view showing a scanning waveform of a sound wave frequency change in the method of the present invention and the conventional method, and FIG. 3 is an explanatory view schematically showing the conventional method. 11 …… Light source 12 …… Acousto-optic device 13 …… Acousto-optic element 14 …… Imaging optics 15 …… Breaker 16 …… Sound wave drive circuit 17 …… Voltage control circuit 18 …… Voltage correction circuit section 19 …… Inverse tangential wave generation circuit section 20 …… photoreceptor (photoreceptor) 21 …… image plane L ₁ …… light beam L ₂ …… light beam

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yusaku Hinoki 2-9-15 Futaba, Shinagawa-ku, Tokyo Furukawa Electric Co., Ltd. Central Research Laboratory (56) Reference JP-A-52-68307 (JP, A) ) Japanese Patent Laid-Open No. 55-25081 (JP, A) Shoukai 61-137916 (JP, U)

Claims (5)

[Claims] 1. An acousto-optic device, a sound wave drive circuit for the acousto-optic device, and a voltage control circuit are provided as deflection scanning means for a light beam, and a light beam transmitted through the acousto-optic device is imaged on an imaging surface. In the deflection type light beam scanning method in which an image forming optical system is provided as an image forming means and a light beam is scanned through these means while scanning the image forming surface, an acousto-optical element is driven through a sound wave drive circuit. At this time, the deflection type light beam scanning method is characterized in that the frequency sweep waveform of the sound wave output is controlled by a voltage control circuit to scan the light beam on the image forming surface at a constant speed. 2. The deflection type light beam scanning method according to claim 1, wherein the acousto-optic element is a bulk type. 3. The deflection type light beam scanning method according to claim 1, wherein the acousto-optic element is a thin film laminated type. 4. The deflection type light beam scanning method according to claim 1, wherein the voltage control circuit comprises an arctangent wave generation circuit. 5. The deflection type light beam scanning method according to claim 1, wherein the voltage control circuit comprises a voltage correction circuit section and an arctangent wave generation circuit section.