JPH10115795A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical scanning device which can make an optical scan at a high frequency without making the diameter of a torsion spring large and is reducible in size. SOLUTION: The torsion spring 2 is extended in a housing 4 while having a magnet 8 and a polygon mirror 10 fixed in its center. A coil 16 is arranged outside it and an alternating current is supplied to produce an alternating magnetic field, thereby vibrating the magnet 8. The laser beam 12 emitted by a light source 24 is reflected by the respective reflecting surfaces of the polygon mirror 10 to scan a scanned surface 26 with the light. Consequently, a high scanning frequency is obtained relatively easily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning technique used for office equipment such as a laser printer, a bar code reader, and a laser scan micrometer, and a measuring instrument.

[0002]

2. Description of the Related Art Conventionally, as an optical scanning device provided with a mirror with a magnet and a coil for generating an alternating magnetic field, there is Japanese Patent Application No. 7-296788 proposed by the Company. This utilizes a superelastic alloy wire with a magnet and a resonance phenomenon caused by an alternating magnetic field, and the configuration is shown in FIG.

[0003] In brief, the mirror 28a with a magnet whose surface is mirror-finished to reflect light is a superelastic alloy (a type of shape memory alloy whose reverse transformation temperature af point is set to room temperature or lower). It is adhesively fixed to a torsion spring 2a made of a Ni-Ti alloy. Further, the torsion spring 2a is smaller than the permanent deformation critical stress in order to exhibit the superelastic effect in the stress-induced martensite phase,
It is attached to the housing 4a by the fixing jig 6a in a state where it is pulled by a tension that generates a predetermined stress larger than the stress-induced transformation critical stress.

A coil 16a is wound around the core 14a. The coil 16a has a screw hole 18a provided in the core 14a and a hole 20a provided in the housing 4a.
a with a magnet (not shown) through a
It is fixed behind a. Alternating pulse current generator 22
a and the coil 16a generate an alternating magnetic field around them, and oscillate the mirror with magnet 28a. When the frequency ω of the alternating pulse current and the mechanical natural frequency ω0 of the torsion spring 2a and the mirror with magnet 28a match, the mirror with magnet 28a causes resonance oscillation. The laser beam 12a emitted from the light source 24a is reflected and scanned by a mirror with a magnet that resonates and vibrates.

[0005]

However, according to the above-mentioned prior art, when the reflecting mirror (mirror with magnet) is caused to resonate and vibrate at a higher frequency in order to realize high-speed optical scanning, the size of the mirror with magnet is reduced. Therefore, it is necessary to reduce the moment of inertia or increase the diameter of the torsion spring to increase the spring constant. Here, since there is a limit to the former miniaturization, increasing the diameter of the torsion spring to increase the spring constant has been a practical and effective method for realizing high-speed optical scanning. However, a torsion spring made of a superelastic alloy must be used with a stable operating point in the martensite phase by applying a tension so as to generate a predetermined stress. Therefore, when the diameter of the torsion spring is increased, it is necessary to increase the tension in proportion to the cross-sectional area of the torsion spring, that is, the square of the spring diameter. At this time, the housing for fixing the torsion spring must have a large thickness and high rigidity.
There is a major problem that it is difficult to reduce the size and weight of the entire device including the housing.

[0006] Even when optical scanning is performed by vibrating at a frequency other than the mechanical natural frequency of the vibration system, it is desirable that the diameter of the torsion spring be large in order to withstand high-frequency vibration, and the housing portion is small and lightweight. There was a problem that conversion was difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides an optical scanning device which can perform optical scanning at a high frequency without having to increase the diameter of a torsion spring and which can be miniaturized. The purpose is to:

[0008]

In order to achieve the above object, an optical scanning device according to the present invention comprises a light source for emitting a light beam, a magnet swingably supported with respect to a housing, and A multi-mirror body pivotally supported by the housing and configured by a number of mirrors reflecting the light beam; a fulcrum for supporting the magnet and the poly-mirror body and supporting vibration of the magnet and the polyhedral mirror; A torsion spring made of a shape memory alloy fixed to the housing with a predetermined tension applied to the housing, and a magnetic field generating means for generating an alternating magnetic field to swing the magnet.

With such a configuration, when the magnetic field generating means generates an alternating magnetic field, the alternating magnetic field:
A torque is applied to the magnet fixed to the torsion spring, and the magnet and the poly-mirror vibrate due to a periodic alternating magnetic field. The torsion spring generates a torsional stress and receives a maximum restoring force at the peak of the alternating magnetic field. In particular, when the mechanical natural frequency of the vibration system including the torsion spring, magnet, multi-mirror body, and the like and the frequency of the alternating current coincide, resonance occurs, and the amplitude can be maximized. The reflection surface of the multi-mirror body is composed of a large number of surfaces, and the light beam emitted from the light source is sequentially reflected by different mirror surfaces, so that light scanning is performed several times with one vibration. As a result, optical scanning is performed at a frequency several times that of the vibration frequency of the magnet and the multi-mirror body.

According to a second aspect of the present invention, there is provided an optical scanning device, comprising: a light source that emits a light beam; a magnet having a plurality of mirror surfaces that are swingably supported with respect to a housing and reflect the light beam; And a torsion spring made of a shape memory alloy fixed to a housing under a predetermined tension so as to be a fulcrum of vibration of the magnet, and an alternating magnetic field for swinging the magnet is generated. And a magnetic field generating means. With such a configuration, when the magnetic field generating means generates an alternating magnetic field, the magnet vibrates by the same operation as the device of claim 1, and the light beam is reflected by a large number of reflecting surfaces on the magnet. As a result, optical scanning is performed at a frequency several times higher than the vibration frequency of the magnet.

According to a third aspect of the present invention, there is provided an optical scanning device according to the first or second aspect, wherein the magnetic field generating means includes:
It is detachably attached to the housing and arbitrarily arranged around the magnet. With such a configuration, the housing and the magnetic field generating means can be freely arranged in a limited space, and the distance between the magnetic field generating means and the magnet can be freely changed. Becomes variable, and as a result, the scanning width also becomes variable.

According to a fourth aspect of the present invention, there is provided an optical scanning device comprising:
Or the optical scanning device according to 3, wherein the magnetic field generating means includes a coil configured by winding an electric wire around a core member and a power supply for flowing a predetermined current through the coil.
The coil is configured to be supplied with a rectangular wave current to generate an alternating magnetic field. With such a configuration, when a rectangular wave current is supplied to the coil, an alternating magnetic field is generated such that torque is applied to the magnet until the elastic restoring force of the torsion spring is maximized. Magnets oscillate with large amplitudes. As a result, a large scanning width is obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of the optical scanning device of the present invention. The torsion spring 2 is fixed to the housing 4 by a fixing jig 6 while being pulled by an appropriate tension. At the approximate center of the torsion spring 2, a magnet 8 and a polyhedral mirror 10, which is a polymirror, are fixed with an adhesive (not shown). The magnet 8 is made of, for example, Ni-Co (nickel cobalt) or Sm-Co (samarium cobalt) having a thickness of 0.3 mm, a length of 3 mm, and a width of 6 mm.

The polyhedral mirror 10 has, for example, three reflecting surfaces as shown in FIG. 2, and is made of aluminum or the like whose mass of inertia is negligible as compared with the magnet 8. The reflecting surface of the polyhedral mirror 10 is mirror-finished to reflect a laser beam 12 described later. Instead of mirror-finish the reflecting surface of the polyhedral mirror 10, a mirror may be attached to the reflecting surface of the polyhedral mirror 10 by bonding or the like. In FIG. 2, the widths a and b of each reflecting surface and the size of the angle c formed by each reflecting surface are determined by the magnet 8.
And a constant determined by the deflection angle and scanning width of the polyhedral mirror 10. The torsion spring 2 is made of a Ni-Ti alloy and has a size of, for example, a wire diameter of about 140 μm and a length of about 10 mm. Since the torsion spring 2 is pulled with a tension such that the superelastic alloy is stably positioned in the martensite phase, the magnet 8 and the polyhedral mirror 10 fixed at the center of the torsion spring 2 swing vertically and horizontally. There is no. On the other hand, a coil 16 is wound around the core 14, for example, about 300 turns. Coil 1
6 is fixed to the housing 4 by a screw (not shown) through a screw hole 18 provided in the core 14 and a hole 20 provided in the housing 4. Then, when a current of about 100 mA at 3 V, for example, is applied to the coil by the pulse current generator 22, an alternating magnetic field is generated, and the magnet 8 and the polyhedral mirror 10 vibrate. The laser beam 12 emitted from the light source 24 is reflected by each reflecting surface of the polyhedral mirror 10, and is scanned on the surface 26 to be scanned by the resonance of the magnet 8.

Next, the operation will be described.

When a pulse current as shown in FIG. 1 is applied to the coil 16, an alternating magnetic field is generated in front of and behind the coil 16. The magnet 8 fixed at the center to the torsion spring 2 and installed in front of the coil 16 receives a torque of MHcos θ by the alternating magnetic field. (M is the magnetic moment of the magnet 8, H is the strength of the magnetic field, θ is the deflection angle.) In the case of the torsion angle θ, the restoring force k by the torsion spring 2
also receives θ. (K: spring constant) Further, when the magnet 8 and the polyhedral mirror 10 vibrate at high speed, a damping force proportional to dθ / dt is also received due to frictional resistance with air and frictional resistance inside the torsion spring 2.
When the torque is applied periodically (angular frequency ω), the magnet 8 starts torsional vibration. When this vibration system is represented by an equation, it becomes Equation 1.

[0018]

(Equation 1)

This is an equation in the case where a forcing force is applied to the damped vibration system, and its general solution is expressed by Equation 2. In addition,
The inertial mass of the polyhedral mirror 10 was ignored.

[0020]

(Equation 2)

That is, when the frequency ω of the current and the natural frequency ω0 of the mechanical system composed of the magnet and the torsion spring coincide with each other, a so-called resonance state occurs, and the maximum deflection angle is obtained.

By changing the wire diameter φ of the torsion spring and the mass m (more precisely, the moment of inertia) of the magnet, optical scanning devices of various frequencies can be manufactured. Furthermore, as can be seen from the coefficient MH / I in Equation 2, the use of magnets of various strengths (M) or magnetic fields of various amplitudes (H = ni, n: number of coil windings i: current), By applying the current i, an optical scanning device having a desired deflection angle can be manufactured according to the target electric product or electronic device.

As shown in FIGS. 3 (a), 3 (b) and 3 (c), the laser beam 12 emitted from the light source 24 is reflected by each reflecting surface of the polyhedral mirror 10, and the scanned surface 26 Is scanned. In the present embodiment, the magnet 8 is moved three times by one stroke, that is, six times by one reciprocation.
Light scanning can be performed twice. Thus, for example, a frequency of 900
1/3 of 300H for laser printers, image scanners, etc. that require optical scanning of about
It can be applied at a vibration frequency of about z.
The light scanning angle is about 1/3 of the deflection angle of the magnet 8, but a desired scanning width can be obtained by adjusting the strength of the magnetic field and the optical path length.

The above embodiment is an example of realizing an optical scanning device, and those skilled in the art can make various modifications without departing from the spirit of the present invention.

For example, in the present embodiment, in the shape of the polyhedral mirror, the reflection surface is realized by using one having three surfaces. However, the reflection surface has two surfaces in accordance with the target electric product or electronic device. It can be implemented using any of the four or more surfaces.

In the present embodiment, the polyhedral mirror 10
And the magnet 8 are separately attached to the torsion spring, but the polyhedral mirror 10 may be attached to the magnet 8 with an adhesive or the like to be integrated. Further, the magnet 8 itself may be processed into a shape like the polyhedral mirror shown in FIG. 2, and the surface thereof may be subjected to a process such as aluminum vapor deposition to serve also as a polyhedral mirror.

In this embodiment, the torsion spring 2, the magnet 8, and the polyhedral mirror 10 are arranged in front of the coil 16 for convenience. However, an alternating magnetic field around the coil 16 is substantially perpendicular to the magnetic moment M of the magnet 8. It can be placed anywhere where it occurs.

Further, in the present embodiment, the housing 4 to which the torsion spring 2, the magnet 8, and the polyhedral mirror 10 are fixed is fixed to the coil 16 by screws, but this may be detachably mounted. As a result, for example, the coil 16, the light source 24, the scanned surface 26, and the like can be arranged on the reflection surface side of the polyhedral mirror 10. Further, by making the distance between the coil 16 and the magnet 8 variable, the magnitude of the alternating magnetic field becomes variable, and as a result, the scanning width can also be made variable.

Further, in the present embodiment, the waveform of the current flowing through the coil 16 is a rectangular wave. When the absolute value of the current value becomes maximum, the torsion angle θ of the magnet 8 becomes maximum, and the restoring force kθ (k: spring constant) by the torsion spring 2 also becomes maximum. With a rectangular wave, torque can be applied to the magnet 8 until the restoring force of the torsion spring 2 is maximized. Further, since the scanning width can be maximized at the lowest current value, the energy efficiency is the best. However, if there is enough scanning width, a periodic waveform such as a SIN wave or a triangular wave may be used.

Further, in this embodiment, the optical scanning device is configured by utilizing the resonance phenomenon in order to minimize the current flowing through the coil 16. However, if there is enough power, the optical scanning device is removed by removing the resonance point. There is no functional problem with driving the device.

[0031]

As is apparent from the above description, according to the optical scanning device of the first aspect, the laser beam is reflected by the multi-specular body. The reflection surface of the multi-mirror body is composed of a plurality of mirror surfaces, and light scanning is performed several times with one vibration, so when using a torsion spring with the same diameter, when using a simple plane mirror Optical scanning at several times the frequency becomes possible. Accordingly, high-speed scanning can be realized while holding down the tension of the torsion spring, and there is an advantage that the housing is relatively small and lightweight.

Further, according to the optical scanning device of the second aspect, the shape of the magnet itself is made to be a polyhedron and also functions as a mirror. For this reason, there is an advantage that the number of parts is reduced, the assembly of the fine vibration portion is simplified, and mass productivity is improved, which can be expected to lead to cost reduction.

According to the optical scanning device of the third aspect, since the coil is detachably mounted on the housing and arbitrarily arranged around the magnet, both can be freely arranged even in a limited space. The alternating magnetic field from the coil placed outside can cause a vibration system including a magnet, a torsion spring, and the like to generate a desired vibration without being limited by a space and perform optical scanning. Further, since the distance between the coil and the magnet can be freely changed, the strength of the alternating magnetic field is also variable, and as a result, there is an advantage that the adjustment of the scanning width becomes easy.

According to the fourth aspect of the present invention, since the alternating current waveform flowing through the coil is a rectangular wave, torque can be applied to the magnet until the elastic restoring force of the torsion spring is maximized. The width can be maximized. Furthermore, since the scanning width can be maximized with a low current, there is an advantage that an optical scanning device with the best energy efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a shape of a polyhedral mirror used in the present invention.

FIG. 3 is a top view showing a state in which a laser beam is reflected by a polyhedral mirror used in the present invention and light scanning is performed.

FIG. 4 is a diagram showing a conventional optical scanning device.

[Explanation of symbols]

 2 Torsion spring 4 Housing 6 Fixing jig 8 Magnet 10 Polyhedral mirror 12 Laser beam 16 Coil 24 Light source

Claims (4)

[Claims] 1. A light source that emits a light beam, a magnet that is swingably supported by a housing, and a plurality of mirror surfaces that are swingably supported by the housing and reflect the light beam. And a polygonal mirror, which supports the magnet and the polygonal mirror, and is fixed to a housing under a predetermined tension so as to be a fulcrum of vibration of the magnet and the polygonal mirror. An optical scanning device comprising: a torsion spring; and a magnetic field generating means for generating an alternating magnetic field to swing the magnet. 2. A light source for emitting a light beam, a magnet having a plurality of mirror surfaces that are swingably supported with respect to the housing and reflect the light beam, and support the magnet and vibrate the magnet. A torsion spring made of a shape memory alloy and fixed to the housing under a predetermined tension so as to serve as a fulcrum, and magnetic field generating means for generating an alternating magnetic field to swing the magnet. An optical scanning device characterized by the above-mentioned. 3. The optical scanning device according to claim 1, wherein the magnetic field generating unit is detachably attached to the housing and arbitrarily arranged around the magnet. 4. The magnetic field generating means includes a coil formed by winding an electric wire around a core member, and a power supply for supplying a predetermined current to the coil. 4. The optical scanning device according to claim 1, wherein a rectangular wave current is supplied.