JPH09218372A - Optical scanning device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the optical scanning device which prevents a torsion spring supporting a magnet from being broken and is them extremely superior in durability, made small-sized and lightweight, and inexpensive. SOLUTION: Shape memory allow which has a high fatigue limit and inverse transformation temperature above room temperature is employed for the torsion spring 5, and the small magnet 3 which is specularly finished is fitted to the center of the spring. A coil is placed outside it, and an alternating current is supplied to produce an alternating magnetic field, thereby making the specularly finished small magnet 3 resonate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
The present invention relates to an optical scanning device used for office equipment such as a barcode 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 one disclosed in Japanese Patent Application No. 7-296788 filed by the present applicant. This utilizes a resonance phenomenon due to a superelastic alloy wire with a magnet and an alternating magnetic field, and has a structure as shown in FIG. The basic configuration except the material characteristics is the same as that of the present invention.

In brief, the mirror 3a with a magnet whose surface is mirror-finished for reflecting 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 5a made of Ni-Ti. Further, the torsion spring 5a is attached to the housing 1a by the fixing jig 2a while being pulled by a predetermined tension in order to exert superelasticity.

A coil 7a is wound around the core 6a. The coil 7a is passed through a screw hole 8a provided in the core 6a and a hole 4a provided in the housing 1a to the rear of the magnet-equipped mirror 3a by a screw (not shown). It is fixed. 9a is an alternating pulse current generator. The alternating pulse current generator 9a and the coil 7a generate an alternating magnetic field around and vibrate the magnet-equipped mirror 3a. When the frequency ω of the alternating pulse current and the mechanical natural frequency ω ₀ composed of the torsion spring 5a and the magnet-equipped mirror 3a match, the magnet-equipped mirror 3a causes resonance vibration. 10a
Is a laser beam, which is reflected and scanned by the mirror 3a with a magnet that is resonantly oscillating.

[0005]

However, in the above-mentioned conventional example, although the superelastic alloy used as the torsion spring has a relatively high fatigue limit and excellent durability, the fixing portion between the torsion spring and the housing is excellent. When the stress is concentrated on the magnet, and the stress due to the torsional vibration is further applied to the place where the magnet is subjected to the resonance vibration, the torsion spring may be broken.

The present invention has been made in order to solve the above-mentioned problems, and sets the reverse transformation temperature Af point of the shape memory alloy used as the torsion spring at room temperature or higher to increase the permanent deformation critical stress. In addition, by stably setting the elastic constant with respect to temperature change, the torsion spring at the fixed part with the housing can be prevented from breaking, without impairing the excellent characteristics of the shape memory alloy. It is also an object of the present invention to provide an inexpensive optical scanning device that is small and lightweight.

[0007]

In order to achieve this object, an optical scanning device according to a first aspect of the present invention has a torsion spring stretched and supported on a housing and fixed to an intermediate portion of the torsion spring. The magnet supported by the magnet is vibrated by the action of the magnetic field formed by the magnetic field generating means with the torsion spring as an axis, and the mirror surface fixed to the magnet is vibrated to emit the light beam emitted from the light source to the mirror surface. Is made to scan the light beam based on the vibration of the mirror surface, and the torsion spring is made of a shape memory alloy. According to this, when a magnetic field is generated by the magnetic field generating means, this magnetic field gives a torque to the magnet supported by the shape memory alloy, while the magnet receives a restoring force from the torsion spring made of the shape memory alloy. By applying a periodic magnetic field, the magnet can be vibrated. In particular, when the mechanical natural frequency of the vibration system including the torsion spring and the magnet coincides with the frequency of the generated magnetic field, resonance occurs and the amplitude is maximized. Since the mirror surface is integrally formed on the surface of the magnet, the light beam incident on the mirror surface is reflected, and the light beam is scanned in the direction orthogonal to the vibration axis.

Further, in the optical scanning device according to the second aspect of the present invention, the torsion spring has a reverse transformation temperature of room temperature or higher Ni.
Shape memory alloys such as _Ti series and Cu_Zn series are adopted. Therefore, this torsion spring is always in the martensite phase at room temperature, has a higher fatigue limit than the superelastic alloy used in the conventional example, and enables long-life optical scanning without breakage at the housing fixing portion or the like.

Further, the optical scanning device according to claim 3 is
The torsion spring is fixed to the housing in a state in which a predetermined tension is applied, the torsion spring can be surely made into a martensite phase by a tension having a desired elastic coefficient, and is not largely affected by a change in room temperature, The light beam is scanned at a stable resonance frequency.

Further, in the optical scanning device according to a fourth aspect of the invention, the magnetic field generating means can be detached from and separated from the housing, and both can be freely arranged even in a limited space.
The magnetic field of the magnetic field generating means placed outside can cause resonant vibration at a desired resonant frequency to scan a light beam in a vibrating system composed of a magnet and a torsion spring without being restricted by space. .

Further, the optical scanning device according to claim 5 is
The magnetic field generating means comprises a coil formed by winding an electric wire around a core member and a power source for flowing a predetermined periodic current through the coil, and the waveform of the periodic current is a rectangular wave. Since the magnet can be torqued until the restoring force is maximized, the scan width is maximized.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION 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 this embodiment. The small magnet 3 has a length of 4 mm and a width of 8 mm
Is a small magnet made of Ni_Co (nickel cobalt) or Sm_Co (samarium cobalt) having a thickness of 0.4 mm, and its surface 3a is mirror-finished to reflect a laser beam described later. In addition, this small magnet 3
May be single or plural, and instead of mirror-finishing the surface of the small magnet 3, a mirror may be attached to the surface of the small magnet 3 by adhesion or the like. This small magnet 3 is about 100
It has a residual magnetic flux density of about 00 Gauss. Small magnet 3
A torsion spring 5 made of Ni_Ti, which is the shape memory alloy of the present invention, is attached to the back surface of the mirror surface 3m in FIG. The wire diameter of this torsion spring 5 is about 300μ.
m and the length is about 25 mm. The torsion spring 5 has its upper and lower ends fixed to a rectangular housing 1 whose center is hollowed out in a rectangular shape by a jig 2.

With respect to the housing 1, the torsion spring 5
A method for supporting the small magnet 3 will be described.

First, the torsion spring 5 is shown by an arrow a in FIG.
In the state of being pulled by the stress shown in FIG. This stress is set to about half the critical stress for permanent deformation. Then, near the center of the torsion spring 5 fixed in this way,
The small magnet 3 described above is fixed with an adhesive.

On the rear surface of the housing 1, a coil 7 as a magnetic field generating means of the present invention is provided. This coil 7 has 300 turns / c around the cylindrical core 6.
A winding having a density of m is provided, and is screwed to the housing 1 through a screw hole 8 formed in the core 6 and a hole 4 formed in the housing 1. An alternating pulse current generator 9 is connected to both ends of the winding of the coil 7, and a current of about 100 mA at 5 V can be passed through the coil 7. That is, by applying the current to this coil, 300 [turns / cm] × 100 [mA] =
An alternating magnetic field of 3000 [A / m] can be applied.
Then, by applying a predetermined rectangular wave current to the coil 7 by the alternating pulse current generator 9, the small magnet 3 resonates by a mechanism described later, and the small magnet 3 is emitted from a light source (not shown) and incident on the mirror surface 3m of the small magnet 3. Laser beam 10
It is scanned at a predetermined scanning angle.

By the way, the material of the torsion spring 5 in this embodiment is a Ni_Ti alloy which is a kind of shape memory alloy as described above. In this embodiment, a predetermined tension is applied and the arrow a in FIG. It is attached to the housing 1 in the state of the martensite phase shown. Since this shape memory alloy takes various states depending on stress and temperature, the phase transformation of the shape memory alloy will be mainly described below with reference to FIGS. 2 and 4.

FIG. 2 is a diagram showing the phase transformation of the shape memory alloy with respect to temperature and stress. In general, shape memory alloys
Reverse transformation start temperature As point and reverse transformation end temperature A shown in FIG.
It is divided into a shape memory region and a superelastic region at the point f. When used at a temperature lower than the reverse transformation start temperature As point, a so-called shape memory effect is exhibited, and at a temperature higher than the reverse transformation end temperature Af point, a superelastic effect is exhibited. The transformation temperature means the state of the alloy from the austenite phase ((1) state of FIG. 4 (b) and γ state of FIG. 2) to the martensite phase ((2) and (3) of FIG. 4 (b)). 2 and the state of α and β in FIG. 2), and the reverse transformation temperature is the temperature when the martensite phase changes to the austenite phase. As shown in FIGS. 2 and 4, the martensitic transformation in the shape memory alloy can occur due to temperature and stress. In this embodiment,
The shape memory region of the martensite phase generated by temperature is used.

In order to explain the fatigue characteristics of shape memory alloys,
Differences in deformation between a normal metal material and a shape memory alloy under shear stress will be described with reference to the schematic diagram of FIG.

In the case of ordinary metal materials, when the shear stress as an external force exceeds the limit, atoms slip adjacent to each other as shown in FIG. 4 (a), and shear strain occurs. In this case, even if the external force is removed, the strain is not stable because it is energetically stable. That is, as stress is applied repeatedly, this strain accumulates and eventually leads to fracture, commonly referred to as metal fatigue.

On the other hand, when an external force is applied to the shape memory alloy, there are two cases depending on the relationship between the use temperature and the reverse transformation temperature (hereinafter referred to as Af point). One is the case where the Af point is lower than the operating temperature (usually room temperature), and the other is the opposite case. When the Af point is at room temperature or lower, as shown in FIG. 4B, when stress is applied, a phase transformation occurs due to the stress, and the stress-induced martensite phase, that is, the superelastic region is reached. At this time, although the crystal structure of the shape memory alloy is deformed, it does not slide adjacent to each other unlike the atoms of the ordinary metal material described above. Further, when the external force is removed, the martensite phase (β in FIG. 2) above the reverse transformation temperature is energetically unstable, and therefore tries to return to the austenite phase (γ in FIG. 2) again. Therefore, even if the metal is repeatedly subjected to repeated stress to the extent of destruction, in the case of the shape memory alloy, phase change that changes the crystal structure occurs, so that the fracture does not occur. However, at the wire fixing part, several kg are used to maintain the tensile tension.
It is already tightened by the force of f, and a compressive stress of several tens of kgf / mm ² is already applied before the shear stress due to torsion is applied. If a larger shear stress is repeatedly applied in such a state, the permanent deformation critical stress shown in FIG. 2 may be exceeded and fracture may occur.

On the other hand, when the Af point is higher than the operating temperature (room temperature) (for example, 60 ° C.), it is always in the martensite phase state at room temperature, and as shown at point b in FIG. Get higher Further, in the martensite phase in that case, sibling crystals represented by A and B are generated as shown in (2) of FIG. The boundary between A and B (twin plane) is relatively soft because it moves with low stress, and when an external force is applied, a sibling A having a preferred orientation to the external force grows, and as a result, shear deformation occurs. Become. When the external force is unloaded, it is not completely restored to the original state, but in the case of the present embodiment, the torque in the opposite direction is immediately applied by the alternating magnetic field, so that the original state is completely returned. That is, the external force and the restoring force make a reciprocating movement between (2) and (3) in FIG. The load in this case is a combination of the external force that the small magnet 3 receives from the alternating magnetic field and the restoring force from the torsion spring 5.

The present embodiment skillfully utilizes such a property of the shape memory alloy in which the Af point is set to room temperature or higher, for example, 60 ° C., particularly the martensite phase. That is,
When the torsion spring 5 is fixed to the housing 1 by the tension indicated by the arrow a in FIG. 2, compressive stress due to the tension and tightening force and shear stress due to torsional vibration are applied to the fixing portion as in the conventional example. The permanent deformation does not reach the critical stress and does not break.

Further, in FIG. 2, for the sake of convenience, the permanent deformation permanent stress straight line σ _C (PERM) and the stress-induced transformation critical stress straight line σ _{C are shown.}
Although (SIM) is shown by one straight line, there is actually a width, and particularly in the stress-induced transformation critical stress straight line σ _C (SIM), it is a two-phase state in which both a martensite phase and an austenite phase exist. . Therefore, in this embodiment,
The torsion spring 5 is configured to be applied with a tension about half of the permanent deformation critical stress at room temperature, separated from the two-phase state, and completely operated in the martensite phase. In the two-phase state, the transverse elastic modulus becomes unstable with respect to temperature change, but becomes stable in the perfect martensite phase.
The point indicated by C is the operating point of the torsion spring 5 of this embodiment. Therefore, stable optical scanning can be obtained by causing resonant vibration at this operating point. Moreover, since the elastic modulus in the martensite phase is smaller than the elastic modulus in the austenite phase, the small magnet 3 vibrates more even when an alternating magnetic field having the same strength is applied.

Further, the above-mentioned Af point can be freely designed by adjusting the Ni concentration and mixing of impurities as shown in FIG. The same can be said for other shape memory alloys.
In the case of a Ni_Ti alloy, a shape memory alloy having a reverse transformation temperature of about 60 ° C. can be designed by setting the Ni concentration to about 49.7%.

Further, in order to show the stability of the transverse elastic modulus in the temperature change of that region, FIG. 6 shows the relationship between the elastic modulus of this alloy and the temperature.

The graph shown in FIG. 6 shows the relationship between the elastic modulus and the temperature when there is no load, that is, when the tension is 0. At the transformation point (two-phase region), the elastic modulus changes rapidly, but the martensite phase changes. , And the austenite phase have stable and almost constant values. In other words, even when the torsion is repeatedly applied in the martensite phase of the present embodiment, the elastic modulus at that time is stable against the temperature change of the ambient temperature (mainly room temperature), so that the restoring force of the torsion spring 5 and the external alternating magnetic field. The frequency of the resonance vibration of the small magnet 3 generated by and is also stable.

Next, the operation of the optical scanning device having the above configuration will be described.

As shown in FIG. 1, when an alternating pulse current is passed through the coil 7, a coil 7 is formed around the coil 7 as shown in FIG.
As shown in (b), a so-called alternating magnetic field H is formed. The small magnet 3 whose center is fixed to the torsion spring 5 and which is installed in front of the coil 7 receives a torque of MH cos θ due to the alternating magnetic field (where M is the magnetic moment of the small magnet 3 and H is the magnetic field). Strength, θ is the deflection angle). Further, when the torsion angle is θ, the restoring force kθ by the torsion spring 5 is also received (where k is the spring constant of the torsion spring 5). Furthermore, when the small magnet 3 vibrates at high speed, a damping force proportional to dθ / dt is also received due to frictional resistance with the air, frictional resistance inside the torsion spring 5, and the like. Then, when the torque is applied periodically (angular frequency ω), the small magnet 3 starts torsional vibration. When this vibration system is expressed by an equation, the following equation is obtained.

I · d ² θ / dt ² + C · d θ / dt + k ·
θ = M · H · cos ωt where θ: torsion angle I: moment of inertia of small magnet C: damping coefficient k: spring constant M: magnetic moment H: magnetic field strength ω: frequency of alternating current or alternating magnetic field t: time Is an equation when a forcing force is applied to the damping vibration system, and its general solution is represented by the equation shown below.

Θ = MH / I [(ω ₀ ² −ω ² ) ² + 4μ
² ω ² ] −1 / ² · cos (ωt−α) tan α = ² μω / ω ₀ ² −ω ² μ = C / 2I where I: moment of inertia of small magnet M: magnetic moment H: strength of magnetic field C: Damping coefficient ω ₀ : Natural frequency of vibration system (= (k / m) ^1/2 ) α: Phase delay angle That is, frequency ω of current, small magnet 3 and torsion spring 5
When the natural frequency ω ₀ of the mechanical system consisting of and coincides with each other, a so-called resonance state occurs and the maximum deflection angle is obtained. In the case of this embodiment, the voltage applied to the coil 7 is 5V.
When the current flowing through the winding is about 100 mA, the resonance occurs at a vibration frequency of about 400 Hz, and the deflection angle of the small magnet 3 becomes about 40 degrees. That is, the laser beam 10 reflected by the mirror surface 3 m formed on the surface of the small magnet 3 has a scanning angle of about 8
It is scanned at 0 degrees.

As described above, with such a simple structure, it is possible to provide an optical scanning device having a large scanning angle and stable operation.

The above-described embodiment is an example of realizing an optical scanning device, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above-mentioned embodiment, the shape memory alloy is realized by using the Ni_Ti alloy, but Ag_Cd, A
u_Cd, Cu_Sn, Cu_Al_Ni, Ni_A
Any shape memory alloy that causes thermoelastic martensitic transformation such as l and Fe_Pt can be used.

In the above embodiment, the scanning angle is 80 degrees,
Although the vibration frequency of 400 Hz has been described as an example, the optical scanning device of various frequencies can be realized by changing the wire diameter and length of the alloy, the mass of the small magnet, and the like. For example, consider the case of manufacturing a scanning device with an oscillation frequency of 1 kHz. Generally, the resonance frequency ω ₀ is (k / m) ^1/2
And k is proportional to φ ⁴ (φ: wire diameter),
The square of φ will be proportional to the resonance frequency ω ₀ . Considering that in the above example, φ = 300 μm and the resonance frequency is 400 Hz, if a shape memory alloy of approximately φ = 480 μm is used under the same conditions as in the above-described embodiment, an optical scanning device of approximately 1 kHz is manufactured. can do.

Further, in the above embodiment, about 10,000
3000A / for a small magnet 3 with a Gaussian residual magnetic flux density
An alternating magnetic field of m (300 turns / cm × 100 mA) was applied to realize an optical scanning device with a scanning angle of 80 degrees. That is, when used as an optical scanning device of a laser beam printer, a current of about several hundred mA and a magnetic flux density of about several thousand gauss are most practical. By the way, according to the above-mentioned formula, the magnitude of the deflection angle θ largely depends on the coefficient (MH / I), and by using the small magnets 3 having various strengths (magnetic moment M), or Magnetic fields of various amplitudes (H = n
By providing i; n is the number of turns of the coil 7 and i is a current, it is possible to realize an optical scanning device having a desired deflection angle θ according to a product to which the optical scanning device is applied. Specifically, the strength of the magnetic field can be easily changed by changing the value of the current passed through the coil 7 or the number of turns of the coil 7, and thus the deflection angle θ can be changed.

In the above embodiment, the torsion spring 5 and the small magnet 3 are arranged on the front surface of the coil 7 for the sake of convenience, but the alternating magnetic field around the coil 7 is substantially orthogonal to the magnetic moment M of the small magnet 3. If it occurs in the direction,
You can place it anywhere.

Further, in the above-mentioned embodiment, the current waveform passed through the coil 7 is a rectangular wave in order to maximize the scanning width, but if the scanning width has a margin, it may be a periodic waveform such as a SIN wave or a triangular wave.

Further, in the above-mentioned embodiment, the optical scanning device is constructed by utilizing the resonance phenomenon in order to minimize the current flowing through the coil 7. However, if the electric power has a margin, the resonance point is removed. There is no functional problem even if the optical scanning device is driven.

[0040]

As is apparent from the above description, according to the optical scanning device of the first aspect of the present invention, the magnet having the mirror surface formed on the surface is supported by the torsion spring made of a shape memory alloy. At the same time, by arranging magnetic field generating means for generating a magnetic field in the vicinity of the magnet, resonance torsional vibration is generated in the magnet due to the action of the magnetic field, and the vibration causes the light beam reflected on the mirror surface to scan. Therefore, an optical scanning device having a very simple structure and a wide scanning angle can be manufactured at low cost. Further, particularly in the present invention, since the shape memory alloy is used for this torsion spring, the fatigue limit can be set to be much higher than that of ordinary metal.
It is possible to provide a long-life optical scanning device.

Further, according to the optical scanning device of the second aspect, since the reverse transformation temperature of the shape memory alloy used as the torsion spring is set to room temperature or higher and the martensite phase generated by the temperature is used, the conventional method is used. The fatigue limit can be set higher than that of the stress-induced martensite phase. Therefore, it is possible to provide an optical scanning device having an extremely long life, in which the fixed portion of the torsion spring where the stress is concentrated does not break.

Further, according to the optical scanning device of the third aspect, since the martensite phase having a stable elastic modulus is used by applying a predetermined tension to the shape memory alloy as the torsion spring, the resonance occurs. The frequency is stable, and the scanning accuracy of the light beam can be improved. Therefore, the light beam can be stably scanned.

Further, according to the optical scanning device of the fourth aspect, since the magnetic field generating means is detachable from the housing, the both can be arranged in a free positional relationship. Therefore, office equipment or the like equipped with this optical scanning device can be manufactured more compactly.

According to the optical scanning device of the fifth aspect, since the magnetic field generating means has a coil and the current waveform applied to the coil is a rectangular wave, the restoring force of the torsion spring is increased. The torque can be applied to the small magnet until the maximum value is maximized, and the scanning width can be maximized. Moreover, since the magnitude of the magnetic field can be changed according to the value of the current flowing through the coil, the scanning angle can be changed by changing the current value, and the optical scanning device can be applied to various types of devices. it can.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a configuration of an optical scanning device according to an embodiment.

FIG. 2 is a diagram showing a phase transformation with respect to temperature and stress of the shape memory alloy used in the present embodiment.

FIG. 3 is a diagram showing stress-strain characteristics of the shape memory alloy used in the present embodiment.

FIG. 4 is a schematic diagram showing shear strain due to phase transformation of the shape memory alloy used in the present embodiment and shear strain of general metal.

FIG. 5 is a transformation point and N of the shape memory alloy used in this embodiment.
It is a figure showing the relationship with i density.

FIG. 6 is a diagram showing a temperature characteristic of an elastic coefficient of the shape memory alloy used in the present embodiment.

FIG. 7 is a schematic diagram in which the small magnet used in the present embodiment receives torque from an alternating magnetic field.

FIG. 8 is a perspective view showing a configuration of a conventional optical scanning device using a superelastic wire having a reverse transformation temperature of room temperature or lower as a torsion spring.

[Explanation of symbols]

 1 Housing 3 Small magnet 3m Mirror surface 5 Torsion spring 7 Coil 9 Pulse current generator 10 Laser beam

Claims (5)

[Claims] 1. A torsion spring is stretched and supported on a housing, and a magnet fixedly supported at an intermediate portion of the torsion spring is vibrated with the torsion spring as an axis by the action of a magnetic field formed by a magnetic field generating means. , By vibrating the mirror surface formed with the magnet and making the light beam emitted from the light source enter the mirror surface,
An optical scanning device that scans the light beam based on vibration of the mirror surface, wherein the torsion spring is made of a shape memory alloy. 2. The optical scanning device according to claim 1, wherein the torsion spring is made of a shape memory alloy having a reverse transformation temperature of room temperature or higher, such as Ni_Ti series or Cu_Zn series. 3. The optical scanning device according to claim 1, wherein the torsion spring is fixed to the housing in a state where a predetermined tension is applied. 4. The optical scanning device according to claim 1, wherein the magnetic field generating means is detachable from the housing. 5. The magnetic field generating means comprises a coil formed by winding an electric wire around a core member and a power source for supplying a predetermined periodic current to the coil, and the waveform of the periodic current is a rectangular wave. The optical scanning device according to claim 1, wherein