JPH08262364A - Optical deflector using shape memory alloy thin film - Google Patents

Abstract

(57) [Abstract] [Purpose] An object of the present invention is to provide an optical deflector using a shape memory alloy thin film that maintains a stable resonance state even when the ambient temperature fluctuates. [Structure] The SMA light deflector 1 takes a U-shaped bent shape by applying a pulse voltage from the function generator 6, and becomes a nearly flat shape by setting the voltage to 0V. By repeating this ON / OFF, SMA
The light deflector 1 mechanically vibrates. This SMA light deflector 1
When the light 16 from the laser diode 15 is incident on the light reflecting surface 17 of the SMA light deflector 1 while the
The reflected light 18 is scanned in the vertical direction. This scanning light 1
Scanning the barcode 19 at 8 functions as a barcode scanner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflector for scanning a light beam, and more particularly to an optical deflector using a shape memory alloy thin film suitable for scanning laser light in a bar code reader. It is a thing.

[0002]

2. Description of the Related Art Today, bar codes for individual recognition are indispensable for swift and reliable management of merchandise in supermarkets and convenience stores, distribution management in transportation, and parts and inventory management in factories. The bar code is one in which light and shade of light is printed on an object, and a one-dimensional bar code is generally used.

Many of such bar code recognition systems scan the bar code with light that is narrowed down and detect the intensity of the reflected light from the bar code at this time with a photodetector.
To construct this system, a light source, an optical system, and a polygon mirror that is a rotating polyhedron that mechanically continuously rotates, or an optical deflector that includes a galvano mirror having a light reflecting surface that reciprocally rotates and oscillates is required. For details on this, see "Applied Optoelectronics Handbook, Shokodo, pp53.
5-537, 1989 "and" Laser Handbook, Ohmsha,
pp378-379, 1982 ".

The polygon mirror is a rotating polyhedron whose side surface has an optical mirror surface, and is rotated around a central axis by a motor. The laser light is incident on the side surface of the rotating polygon mirror, and the reflected light is scanned according to the rotation of the polygon mirror. On the other hand, the galvano mirror is a small mirror that reciprocally rotates and vibrates due to electromagnetic force, and incident light is scanned by the small mirror that reciprocally rotates and vibrates. The galvano mirror is more advantageous than the polygon mirror in terms of downsizing, but it has a problem that the cost is higher than that of the polygon mirror and that the scanning light is blurred due to the shake of the mirror surface during reciprocating rotary vibration.

By the way, a shape memory alloy (hereinafter abbreviated as SMA) thin film has a smaller heat capacity than a bulk material and an increased surface area / volume ratio. Therefore, although it is driven by heat, heating and cooling rates are high. It has the advantage of being fast. Focusing on this point, a technique relating to application of an SMA thin film as a small-sized optical deflector has been filed by the applicant of the present application. In this technique, the SMA thin film is used to drive at a resonance frequency by a cantilever method, so that the SMA having a thickness of 7 μm can be obtained.
A bending angle of about 30 ° was obtained at a frequency of 45 Hz in the thin film.

[0006]

However, since the polygon mirror is heavy and has a large volume, it is unsuitable as a component of a portable, compact and lightweight optical deflector that is used by being attached to a human finger. Is. Therefore, in order to realize a compact and lightweight optical deflector that can be mounted on a human finger, it is necessary to develop a compact and lightweight optical deflector that replaces the polygon mirror and a further compact galvanometer mirror. On the other hand, since the SMA thin film optical deflector is driven by heat, there is a problem that the operating condition changes due to the fluctuation of the ambient temperature and the influence of the wind, and the deflection angle changes or the deflection direction changes.

The present invention has been made in view of the above problems, and an object thereof is to provide an optical deflector using a shape memory alloy thin film that maintains a stable resonance state even when the ambient temperature changes. To do.

[0008]

In order to achieve the above object, an optical polarizer using a shape memory alloy thin film according to a first aspect of the present invention is provided with a current input part, an output part and a heating part by a resistor. And a control means for synchronizing the frequency of the pulse current for driving the light deflecting means with the resonance frequency of the light deflecting means, and at least by the resistor. It is characterized in that the heat generating portion is provided with a shape memory alloy thin film.

The optical deflector using the shape memory alloy thin film according to the second aspect is an optical deflector having an input part and an output part for a current, a heating part by a resistor, and a reflecting part for reflecting light, and the above-mentioned optical deflector. Means for controlling the duty ratio of the pulse current applied to the means within a predetermined range to control the discharge time to be longer than the heating time of the heat generating part, and at least the heat generating part by the resistor has a shape memory. It is characterized by comprising an alloy thin film.

Further, an optical polarizer using the shape memory alloy thin film according to the third aspect is an optical deflector having an input part and an output part for a current, a heat generating part by a resistor and a reflecting part for reflecting light, and Control means for adjusting the pulse current of the light deflecting means so as to maximize the deflection angle of the light deflecting means, and at least a heat-generating part of the resistor is provided with a shape memory alloy thin film. And

[0011]

That is, in the optical polarizer using the shape memory alloy thin film according to the first aspect of the present invention, the frequency of the pulse current for driving the optical deflecting means by the control means is synchronized with the resonance frequency of the optical deflecting means. Let

Further, in the optical polarizer using the shape memory alloy thin film according to the second aspect, the duty ratio of the pulse current applied to the light deflecting means is set within a predetermined range by the control means, and the heating time of the heat generating portion is set. The discharge time is controlled to be long.

Further, in the optical deflector using the shape memory alloy thin film according to the third aspect, the control means adjusts the pulse current of the light deflecting means so that the deflection angle of the light deflecting means is maximized. It

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a shape memory alloy (S
MA; Shape Memory Alloy) Thin film light deflector (hereinafter referred to as S
FIG. 3 is a configuration diagram of an optical deflector suitable for use as a one-dimensional bar code reader using a MA optical deflector).

In FIG. 1, the SMA light deflector 1 includes an optical deflector shown in FIG.
In A, a current input part, an output part, a bent part, and a reflection mirror part are used. The SMA light deflector 1 is made of a TiNiSMA thin film formed by a known sputtering method,
The detailed manufacturing method is as follows.

That is, first, a TiNi thin film having a thickness of 7 to 20 μm is formed on a Si substrate having a (100) crystal plane by a sputtering method using a TiNi alloy target or an individual target of Ti and Ni. The film forming pressure at this time is preferably a low pressure in order to increase the mechanical strength of the TiNi film, and specifically, the TiNi film is formed by sputtering at about 2 mtorr. Next, the Si substrate is cleaved from the back side, the TiNi film is peeled off, and cut into a shape shown in FIG. When shaping the TiNi film into the shape of FIG.
Of course, a method of etching the TiNi film on the Si substrate by photolithography and then removing the Si substrate by alkali etching may be used.

Subsequently, Ti processed into the shape shown in FIG.
The heat treatment (crystallization treatment) for crystallizing the Ni film can be performed by, for example, rapid heating / cooling RTP (Rapid Therml Proces).
Sor) for 30 seconds at a temperature of 800 ° C, and bend 1
3 and 14 are constrained by a jig so as to have a U shape, and after heat treatment (shape memory treatment) at a temperature of 450 ° C. to 550 ° C. for several hours to several tens hours in vacuum, the TiNi film is cured. The oxide film on the surface of the TiNi film formed by the heat treatment is removed with heated sulfuric acid / hydrogen peroxide solution.

After the SMA light deflector 1 shown in FIG. 1 is manufactured in this manner, it is attached to an insulating base material (not shown), and electrical contact is made from the contact pads 2 and 3 with a conductive paste. A protective resistance 5 of about 10Ω is connected to the lead wire 4 attached to the contact pad 2. Then, the pulse waveform is applied to the amplifier 7 from the function generator 6, and the lead wire 1 is output from the output terminals 8 and 9 of the amplifier 7.
A current 12 is applied to the contact pads 2 and 3 of the SMA light deflector 1 via 0 and 11. The SMA light deflector 1
Since the resistance between the contact pads 2 and 3 is as small as 1Ω or less, the protection resistor 5 is inserted in series in the SMA optical deflector 1 to protect the amplifier 7.

2A to 2C show plan patterns, and FIGS. 2D to 2F show cross sections AA ', B in FIGS. 2A to 2C. -B 'and CC' are shown respectively, and a configuration example of the SMA light deflector 1 will be described.

First, in FIGS. 2A and 2D, reference numerals 21 and 22 are current input and output pads made of SMA, reference numerals 23 and 24 are heating elements which are resistors made of the same SMA, and reference numeral 25 is. It is a light reflecting surface (mirror surface) made of the same SMA. This optical deflector is characterized by contact pads 21 and 22 for making electrical contact and a resistor 2
3, 24 and the mirror surface 25 are made of the same SMA thin film.

In the optical deflector shown in FIGS. 2B and 2E, the current input unit 26, the current output unit 27, and the heating elements 28 and 29 made of resistors are formed of the same SMA thin film. Further, the mirror surface 30 is made of a member having high smoothness and flatness and high reflectance. In this configuration, the members forming the mirror surface 30 can be selected independently of the SMAs 26 to 29, so that the SMAs 28 and 2 can be selected.
There is a feature that the flatness of the mirror surface 30 is maintained even when the bending movement of 9 is performed.

Further, in the light deflection portion shown in FIGS. 2C and 2F, the SMA thin film is used only in the bent portions 35 and 36, and the heating element 33 including the electrode pads 31 and 32 and the resistor is formed.
This is an example in which the member forming the and the mirror surface 34 are made of different materials. Bending portions 35 and 3 made of the SMA thin film
6 is heated by a heating element 33 made of a resistor via a flexible insulating member 37.

In addition, a low resistance metal is used for the electrode pad, a high resistance metal such as NiCr or polycrystalline silicon is used as the heat generating member made of a resistor, an SMA thin film is used for the bent portion, and a member having high smoothness and flatness for the mirror surface, respectively. It is also possible to use the optimum material.

Next, referring to FIG. 3, a 20 μm thick SMA (Ti-51.7 at% N) film formed by the above-described sputtering method.
i) The differential scanning calorimetry (DSC) curve of the sample which heat-processed the crystallization process (800 degreeC, 30 second at RTP) and the shape memory process (550 degreeC, 48 hours) was performed to the thin film. This S
MA has heat input and output during phase transformation between an austenite phase which is a high temperature phase and a martensite phase which is a low temperature phase. Therefore, by measuring the heat input and output, the temperature at the time of transformation, that is, the transformation point I understand.

That is, in FIG. 3, a curve 301 is a DSC curve when the temperature of the sample is once raised to 100 ° C. and then gradually lowered. In the curve 301, 28.
A heat release having a peak at 9 ° C. was observed, which corresponds to a phase transformation between an austenite phase and a Rhombohedral phase (hereinafter abbreviated as R phase), which is a type of martensite phase.
From this DSC curve 301, the R phase transformation start temperature (hereinafter,
It can be seen that Rs is abbreviated as 41.5 ° C. and R phase transformation end temperature (hereinafter abbreviated as Rf) is 21.3 ° C.
Therefore, this SMA takes the R phase near room temperature.

On the other hand, the curve 302 is a DSC curve when the temperature of the sample is gradually raised from low temperature. In this curve 302, an endotherm having a peak at 35.1 ° C. is observed, which indicates that the reverse transformation from the R phase to the austenite phase is occurring. This DSC curve 302
From this, it is understood that the austenite transformation start temperature (hereinafter abbreviated as As) is 31.3 ° C. and the austenite transformation end temperature (hereinafter abbreviated as Af) is 39.8 ° C.

The light deflecting portion made of the SMA thin film having the shape shown in FIG. 2A is nearly flat at room temperature (reference numeral 30).
3, the side view is indicated by reference numeral 304). When this is heated on a hot plate, it bends in a U shape (reference numeral 305,
The side view is designated by reference numeral 306). When this is returned to room temperature again, it returns to the original shape (reference numeral 303, reference numeral 304 in the side view). From this, it can be seen that the SMA light deflector 1 of this embodiment exhibits a bidirectional shape memory characteristic.

According to such a principle, when the current 12 actually flows through the SMA light deflecting portion 1, the bending portions 13 and 14 of the SMA light deflecting portion 1 which is in the R phase at room temperature are heated by Joule heat, It transforms to the high temperature austenite phase. Then, in the R phase, the SMA having a shape close to a flat surface
The light deflector 1 transforms into an austenite phase, and thereby recovers the shape-memorized U-shape. As described above, since the SMA light deflecting unit 1 has a two-way shape memory, by turning off the current 12, the SMA light deflecting unit 1 is naturally cooled and returns to the R phase, and the shape becomes nearly flat. . That is, by applying a pulse voltage from the function generator 6 (ON state), the SMA light deflector 1 takes a U-shaped bent shape, and by setting the voltage of the function generator 6 to 0 V (OFF state), the SMA light The deflection unit 1 has a shape that is almost flat.

Further, by repeatedly turning the function generator 6 ON and OFF, the SMA light deflector 1
Will vibrate mechanically. When the light 16 from the laser diode (LD) 15 is incident on the light reflection surface 17 of the SMA light deflector 1 while the SMA light deflector 1 is vibrating, the reflected light 18 is vertically scanned. become. By scanning the barcode 19 with the scanning light 18, the optical deflector shown in FIG. 1 can function as a barcode scanner.

Next, FIG. 4 shows the configuration of a measuring system for examining the vibration characteristics of the SMA light deflecting section, and the description will be given. As shown in the figure, the pulse signal generated by the function generator 42 is amplified by the amplifier 43, and the current 44 becomes 1
It flows into the contact pad 46 of the SMA light deflector 41 through the 0Ω protection resistor 45, passes through the SMA light deflector 41, and then returns from the other contact pad 47 to the amplifier 43.

The SMA light deflector 41 is heated by Joule heat when a current flows, and the shape-memorized bent portions 48 and 49 are bent in a U shape. Then, when the current 44 is cut off, the bent portions 48 and 49 of the SMA light deflection portion 41 try to return to the flat shape.

Actually, even if the current is cut off, the SMA bending portion 4
Since the temperatures of 8 and 49 are cooled by natural heat dissipation, they do not immediately return to a flat shape. The SMA light deflector 41 is electrically heated again before it returns to the shape at room temperature, bends into a U-shape, and then repeats this operation in order to obtain the SM.
The A light deflector 41 generates mechanical vibration.

The laser displacement meter 50 irradiates the subject with light 52 emitted from the LD 51, and reflects light 53 from the subject.
Is detected by the photodetector 54, and the moving distance of the subject is measured. According to the laser displacement meter 50, it is possible to measure the vibration characteristic of the SMA light deflecting unit which is vibrating due to the periodic pulse current heating with the light reflecting surface 55 of the SMA light deflecting unit 41 as a subject.

Here, FIG. 5 is a graph in which the bending displacement of the SMA light deflecting portion 41 generated when the SMA light deflecting portion 41 is energized with a pulse is measured by a laser displacement meter. FIG. 5A is a side view of the SMA light deflector 41 at room temperature (T ≦ Rf).
As shown by the broken line 61, the shape is slightly more angled than flat. Then, FIG. 5C shows a side surface shape of the SMA light deflecting section 41 in a region of temperature T ≧ Af, which has a U-shaped shape (broken line 62) in which the shape is memorized. Therefore, the movable range of the SMA light deflector 41 in this embodiment is shown in FIG.
As shown in (b), it is between the states of broken lines 61 and 62.

What is important when driving the SMA light deflector 41 is to select the amplitude and pulse of the drive current pulse so that the center of vibration 63 is located between the broken line 61 and the broken line 62. If the amplitude and pulse width of the drive pulse are inappropriate, and the SMA light deflector 41 is driven under the condition of overheating, for example, the SMA light deflector 41 is fixed in the shape of the broken line 62, and vibration cannot be obtained.

FIG. 6 shows the relationship among the actual drive current, temperature, and displacement of the SMA light deflector 41. That is, in FIG. 6, reference numerals 64a to 64d are drive current pulses, and accordingly, the temperatures of the heat generating portions of the SMA optical deflector 41 are reference numerals 65a to 6d.
As in 5d, the temperature is raised from room temperature (within Rf) to a temperature of Af or higher. When the current pulse is cut off, the temperature of the SMA light deflector 41 falls to Rf due to natural heat dissipation as indicated by reference numerals 66a to 66d. It is not always necessary to lower the temperature to Rf in actual operation, but it is necessary to lower it to at least As or lower. When the SMA light deflector 41 is cantilevered and driven by a current pulse synchronized with the resonance frequency, a sinusoidal displacement shown by reference numeral 67 is obtained. Reference numeral 68 is a median value of displacement, reference numeral 69 is a maximum value of displacement, reference numeral 70 is a minimum value of displacement, and a distance 71 between the reference numerals 69 and 70 is a displacement amplitude.

Next, FIG. 7 shows the bending displacement characteristics of the optical deflector 41 formed of a 7 μm thick SMA thin film using the measurement system shown in FIG. 4 during pulse driving. In FIG. 7A, the horizontal axis represents the driving frequency [Hz], and the vertical axis represents the displacement meter output (displacement amplitude) [m
m]. A sharp bending displacement peak was observed at 45 Hz, and the vibration of the SMA light deflector 41 at this time was about 30 degrees in angle. The peak frequency of this displacement is considered to be the resonance frequency that depends on the material and shape.
It is known that the resonance frequency fR of the cantilever is given by the following equation (1).

[0038]

[Equation 1]

Here, t is film thickness, l is beam length, E is Young's modulus, and ρ is density. TiNi Young's modulus is 100
Substituting GPa, ρ = 6.5, t = 7 μm, l = 1 cm into equation (1) gives fR 44 Hz, which is
It matches the resonance frequency obtained from the frequency characteristic of the 7 μm thick SMA light deflector 41 shown in FIG. 7A.

On the other hand, FIG. 7 (b) shows a 7 μm thick S
The relationship of the displacement meter output to the duty ratio (pulse width) of the drive pulse at 45 Hz of the optical deflector using the MA thin film is shown. From the figure, it can be seen that there is a maximum value of displacement when pulse driving with a duty ratio of -10%, and this is because the process of heat dissipation determines the response speed of the 7 μm thick SMA optical deflector. Is shown.

FIG. 8A shows the relationship between the drive frequency of the 12 μm thick SMA light deflector and the displacement meter output, and FIG. 8B shows the relationship between the displacement meter output and the duty ratio (pulse width) of the drive pulse. It is a thing. From the figure, 12 μm thick SM
In the case of the A light deflector, it can be seen that the displacement amplitude becomes maximum at 80 Hz (resonance frequency), and the displacement output becomes maximum at a duty ratio of about 10%.

FIG. 9A shows the relationship between the driving frequency of the 20 μm thick SMA light deflector and the displacement meter output, and FIG. 9B shows the relationship between the displacement meter output and the duty ratio (pulse width) of the driving pulse. It is a thing. From the figure, 20 μm thick SM
In the case of the A-light deflector, it can be seen that the displacement amplitude becomes maximum at 125 Hz (resonance frequency), and the displacement output becomes maximum at a duty ratio of about 10%.

From these FIG. 7 to FIG. 9, 7, 12, 20
The μm-thick SMA optical deflector is commonly used to maximize the displacement amplitude of vibration by driving the pulsed current at its resonance frequency, and the duty ratio of the driving pulse is effective to obtain a large displacement amplitude of vibration at around 10%. It turns out that

FIG. 10 shows the relationship between the resonance frequency fR and the film thickness obtained from FIGS. 7 to 9 in the SMA light deflector having a thickness of 7, 12, 20 μm. As is clear from the figure and the above formula (1), fR is proportional to the film thickness. From this, if the frequency necessary for light deflection is clarified, the SMA film thickness with this as the resonance frequency can be known.

Next, FIG. 11 shows the relationship between the drive amplitude and the vibration amplitude in the 20 μm thick SMA light deflector measured in an environment with air-conditioning airflow. Since the driving of the SMA is by heat (temperature), if the temperature of the SMA changes in the blowing condition, the mechanical operating point (the position of the center of vibration 63) changes and the resonance frequency also changes. This is an extremely large problem in stably operating the SMA light deflector driven at the resonance frequency based on the principle of thermal driving.

Next, FIG. 12 is a block diagram showing a first embodiment of the present invention for preventing the mechanical operating conditions of the SMA light deflecting section from varying due to the influence of environmental temperature and wind. As shown in the figure, in order to detect the bending displacement of the SMA light deflector 81, a line sensor or a position detection element (PS
Optical sensor 8 consisting of D; Position Sensitive Detector)
2 is provided to detect the median displacement amplitude, that is, the center of vibration and the displacement amplitude. The positional relationship between the SMA light deflector 81 and the optical sensor 82 is such that when the displacement amplitude of the SMA light deflector 81 is maximized, the position detection light (96, 97 in FIG. 13) from the center position of the vibration is detected by the optical sensor. The light is focused at a predetermined position (for example, the center). The length of the optical sensor 82 is set to be longer than the optical scanning width of the detection light when the displacement amplitude of the SMA optical deflector 81 becomes maximum. From the two pieces of information of the vibration center and the displacement amplitude, the arithmetic circuit 83 obtains the duty ratio, the amplitude, and the offset voltage of the drive pulse so that the displacement amplitude of the SMA light deflector is maximized by the algorithm shown in FIG. Then, based on the result of the arithmetic circuit 83, the waveform generating circuit 84 generates a drive voltage, and the amplifier 85 heats the SMA light deflector 81 by energization.

Here, the displacement detection of the SMA light deflector 81 will be described with reference to FIG. As shown in the figure, the SMA light deflector 91 outputs light 93 emitted from the LD 92.
Enters the reflecting surface 94 of the SMA light deflector 91, and the SM
The bar code 9 is deflected by the bending displacement of the A light deflector 91.
Scan 5. The return light 96, 97 of the scanning light is received by an optical sensor 98 composed of a line sensor or a PSD.
Although the optical system is omitted here for the sake of simplicity, the LD
A collimating lens between 92 and the SMA light deflector 94,
It is possible to insert a lens for collecting the reflected lights 96 and 97. Further, the optical sensor 98 can also serve as the reading CCD line sensor of the barcode reader.

The displacement detecting method of the SMA light deflector can be modified as shown in FIG. That is, FIG.
In the first modified example shown in FIG. 4A, the half mirror 105 is installed in the optical path of the light 104 emitted from the LD 101 and reflected by the light reflecting surface 103 of the SMA light deflecting unit 102, and a part of the scanning light 104 is provided. Is used as the displacement detection light 106 of the SMA light deflector 102, and is guided to an optical sensor 107 composed of a line sensor or a PSD. In this modification, the half mirror 105 is installed near the SMA light deflector 102, so that the scanning width of the detection light 106 can be reduced and the length of the optical sensor 107 can be shortened. Helps reduce size.

The second modification shown in FIG. 14B is characterized in that a second light source 109 is used for detecting displacement of the SMA light deflector 102, in addition to the light deflecting light source 108. And The light emitted from the LD 108 is reflected by the reflecting surface 103 of the SMA light deflector 102, and the scanning light 104
Becomes Light 111 emitted from the second light source LD109
Is irradiated near the bent portion 112 of the SMA light deflector 102, and the reflected light 113 is guided to the optical sensor 107 composed of a line sensor or a PSD. In this modified example, since there is no optical member (corresponding to the half mirror 105 or the like in the first modified example) in the scanning optical path, the light 110 from the LD 108 will have a reflectance of the reflective surface 103 of 100%. ,
The scanning light 104 can be obtained without impairing the intensity. Further, by using the second light source 109, an irradiation site for displacement detection of the SMA light deflector 102 can be arbitrarily selected, so that the optical sensor 107 should be arranged at a position suitable for downsizing the optical deflector. You can

Further, in the third modification shown in FIG. 14C, the displacement detection light is transmitted from the light source 101 to the SMA light deflector 1.
It is characterized in that the light is branched and used before being incident on 02. The light 110 emitted from the LD 101 is branched by the half mirror 114 and becomes branched lights 115 and 116. The branched light 115 is reflected by the reflection surface 103 of the SMA light deflector 102 and becomes scanning light 104. The branched light 116 is reflected by the total reflection mirror 117, and the bent portion 11 of the SMA light deflecting unit 102 is reflected.
The vicinity of 2 is irradiated, and the reflected light 118 is guided to the optical sensor 107 composed of a line sensor or a PSD. By arranging the half mirror 114 and the total reflection mirror 117, the optical path of the displacement detection light can be arbitrarily set, so that the detection light irradiation site in the SMA light deflector 102 can be selected at an appropriate position, and the arrangement of the optical sensor 107 is included. This helps reduce the size of the optical deflector.

Further, in the fourth modified example shown in FIG. 14D, the light 110 emitted from the first light source LD101.
Is reflected by the reflecting surface 103 of the SMA light deflector 102 and becomes scanning light 104. The light 111 emitted from the second light source LD 109 irradiates a surface opposite to the surface 103 on which the scanning light 104 is reflected, and guides the reflected light 119 to an optical sensor 107 including a line sensor or a PSD. The second light source LD109 that generates the displacement detection light can be provided at a position apart from the first light source LD101 that generates the scanning light, and the displacement detection light 111 can be incident on the SMA light deflector 1.
No. 02 heat generating portion 112 and the optical sensor 107 can be arranged behind the SMA light deflecting portion 102, so that space can be effectively used.

Next, referring to the flowchart of FIG.
As a second embodiment, the function of the arithmetic circuit 83 shown in FIG. 12 will be described. First, the resonance frequency of the SMA light deflector 41 is obtained based on the displacement signal of the SMA light deflector 41 including the optical sensor 82 of FIG. This corresponds to the low frequency (3
Driven under the condition that the SMA bent portion is heated to a temperature of Af or higher by a current pulse, and the vibration contained in the displacement signal at that time is obtained from the resonance frequency fR (step S1).

Next, the duty ratio of the drive pulse is 10%,
The drive frequency is fixed at fR, and the drive pulse amplitude is adjusted so that the midpoint of the vibration displacement, that is, the center of vibration is at the center of the displacement sensor. It is assumed that the detection light from the center of vibration when the displacement amplitude is maximum is arranged so as to come to the center of the optical sensor. By this adjustment, the mechanical operating point of the SMA light deflector 41 can be set (step S2).

Subsequently, if the ambient temperature changes or the temperature of the SMA changes due to the influence of the wind, the mechanical operating point of the SMA light deflector 41 changes. When the temperature of SMA rises, SMA
The operating point of the light deflector 41 changes to the bending side (step S
3). At this time, cooling is required, and specifically, the amplitude of the drive pulse is reduced (step S4).

On the other hand, when the temperature of the SMA decreases, the mechanical operating point of the SMA light deflector 41 fluctuates to the flat side (step S3). At this time, the amplitude of the drive pulse is increased or an offset voltage for heating the SMA is superimposed on the drive pulse (step S5). Specifically, as shown in FIG. 16, the offset voltage (FIG. 16 (a)) and the pulse voltage (FIG. 16 (b)) are added together to produce the drive voltage (FIG. 16).
(C)) is generated.

Next, the duty ratio is adjusted so that the displacement amplitude becomes maximum (Amax) (step S6). And
If the vibration amplitude has not decreased compared to Amax, the process returns to step S3, and if it has decreased, the vibration frequency is increased (steps S7 and S8). Then, | ΔA /
If Δf | ≧ K, the process returns to step S3, and if not, it is detected whether the vibration amplitude is further reduced (steps S9 and S10). If the vibration amplitude further decreases, it means that the resonance frequency has changed. Therefore, the vibration frequency is lowered from the vibration frequency at the time of step S7, and if not decreased, the drive frequency is increased (step S1).
1, S12). With the above operation, SM due to changes in ambient temperature
A SM with a drive frequency that suppresses fluctuations in the mechanical operating point of the light deflector and always maximizes the vibration amplitude (displacement amplitude).
The A light deflection unit 41 is driven.

Next, in FIGS. 17 and 18, S having a thickness of 7 μm is used.
Displacement meter output (displacement amplitude) when the MA light deflection unit 41 is driven with a duty ratio of 10% and a drive pulse current of 0.455 A
Shows the drive frequency dependence of the. Resonance frequency fR is 46Hz
And the drive pulse 121a and the vibration displacement 122 at this time
An observation example of a is shown in FIG. In the figure,
The displacement amplitude is indicated by reference numeral 123a, and one drive pulse 1
The displacement amplitude 123a is obtained once per 21a (n = 1).

When the drive frequency is lowered from fR, the displacement amplitude temporarily decreases, but the displacement amplitude peaks again at the frequency of fR / 2. An example of observation of the drive pulse 121b and the vibration displacement 122b at this time is shown in FIG. In the figure, displacement vibration is obtained twice with one drive pulse 121b (n = 2). That is, the drive frequency is fR /
Despite being 2, the frequency of the displacement signal is kept at fR.

Similarly, when the drive frequency is fR / 3, there is a peak in the displacement amplitude, and the drive pulse 121c at this time is present.
An example of observation of the vibration displacement 122c is shown in FIG. From the figure, it can be seen that displacement vibration is obtained three times with one drive pulse (n = 3). As described above, the displacement amplitude 123 has a peak at the frequency of the drive frequency fR / n (n is a positive integer), and at this time, the SMA optical deflector 41 maintains the resonance state. Such a resonance state was observed until n = 6.

When low frequency driving below this is performed, the displacement of the SMA light deflecting section 41 due to thermal driving is observed, and a vibration displacement in which the resonance frequency is superimposed on the large displacement is shown. That is, 3H
Drive pulse 121d and vibration displacement 122 when driven by z
An observation example of d is shown in FIG. From the figure, it can be seen that the resonance frequency of 46 Hz is superimposed on the large displacement vibration. This means that the resonance frequency can be measured by observing the displacement when driving at a low frequency. In the second embodiment, the above method is adopted as a method for obtaining the resonance frequency of the SMA light deflector 41.

Next, FIG. 19 shows a 20 μm thick SMA light deflector 4.
It shows the output of the laser displacement meter when pulse-driven at a cycle of an integral fraction of one resonance frequency. n represents the number of waves that oscillate with one pulse current, and even when n = 6, the displacement output only decreases by about 33%. From the above, even if the SMA light deflector 41 is driven at a frequency that is a positive integer of the resonance frequency fR, if the displacement amplitude is measured in synchronization with the drive pulse, the second embodiment shown in FIG. It can be seen that the method of following the resonance frequency in steps S6 to S12 shown can be used.

The example of using the displacement detecting means by light as shown in FIGS. 13 and 14 has been described above as means for measuring the displacement of the SMA light deflecting section 41 for realizing the first embodiment of FIG. The means for applying the displacement vibration of the SMA light deflector 41 utilizes bending of the SMA by resistance heating. Therefore, if a sensor that detects information about the bending state is provided at the bending portion, it can be used as a means that replaces displacement detection by light.

Next, FIG. 20 shows an example in which a displacement vibration of the SMA light deflector 151 is detected by mounting a thin film thermocouple on the bent portion 152 which is a heat generating portion of the SMA light deflector 151 and measuring the temperature of the SMA. Is shown. 20 (a),
(B) is an enlarged view of a thin film thermocouple mounting portion. Since the SMA light deflector 151 is a thin film of about 7 to 20 μm, the thermocouple is formed of a thin film so that the thermocouple does not become a mechanical load when the shape of the bent portion 152 changes and the heat capacity is reduced. There is a need.

In FIG. 20A, reference numeral 153 is SM.
A and 154 are flexible insulating films, reference numerals 155 and 15
Reference numeral 6 is a member forming a thermocouple, and it is possible to combine chromel, alumel, chromel, constantan, iron, constantan, copper, constantan, or the like. Reference numerals 155 and 156 are used to form a film by a sputtering method, vapor deposition or the like and process it by photolithography. Reference numeral 157
Is a junction in which the thin film thermocouples 155 and 156 are in contact with each other and generate a thermoelectromotive force. From the reference numerals 155 and 156, electrical contact is made on the contact pad 158 of the SMA light deflector 151 and the thermoelectromotive force is measured.

In FIG. 20B, 153 is SMA,
154 is a flexible insulating film, 155, 156 are constituent materials of the thin film thermocouple, 159 is a flexible insulating film, 157.
Is a joint by the contact of 155 and 156. The thermoelectromotive force is generated at the junction 157, and electrical contact is made from the contact pads 155 and 156 on the contact pad 158 of the SMA light deflector 151 to measure the thermoelectromotive force. It is also possible to attach a thin film strain sensor to the bent portion of the SMA light deflector 151.
The reason why the strain sensor is formed of a thin film is the same as that of the thin film thermocouple. The material of the thin film strain sensor is a Cu-Ni alloy or the like, which is formed by sputtering or vapor deposition and processed by photolithography. Two thin film strain sensors are arranged at two bent portions of the SMA light deflector 151, and the longitudinal direction of one thin film strain sensor is the bending direction and the longitudinal direction of the other thin film strain sensor is perpendicular to the bending direction. By compensating for the change in resistance value due to heat generation at the bent part,
It is possible to obtain an output (voltage) proportional to the distortion.
Since the SMA light deflector 151 has a resistance in the heating portion, it is possible to use the change in resistance due to temperature for detecting the displacement of the SMA light deflector 151.

Next, in FIG. 21, in order to solve the problem that the mechanical operating point of the SMA light deflecting unit 201 is changed by the influence of ambient temperature and wind, the SMA light deflecting unit 201 is made of a transparent plastic box 202. It shows a third embodiment of the present invention so as to cover it. The light 204 emitted from the LD 203 is emitted from the SM 205 from the first surface 205 of the box 202.
A light incident on the light reflecting surface 206 of the light deflecting unit 201 and reflected light 2
07 is emitted from the second surface 208 of the box 202. Box 2
Reference numeral 02 denotes a constant temperature bath, and it is preferable to keep the temperature inside the box constant. In order to simply release the heat generated by heating the SMA light deflector 201, for example, the box 2
It is also effective to make a hole in the side surface of 02 to the extent that it does not affect the SMA light deflector 201.

There is also a demand to narrow the deflection angle of the optical deflector when the subject is far away and to widen the deflection angle when the subject is near. In response to this requirement, the SMA optical deflector according to the present invention can obtain a maximum deflection angle when driven at the resonance frequency, and can obtain a small deflection angle by driving at a frequency outside the resonance frequency. it can. In order to adjust the deflection angle, the amplitude of the drive voltage and the offset voltage may be changed in addition to changing the drive frequency.

According to the above embodiment of the present invention, the following constitution can be obtained. (1) Input and output parts of electric current, heat generating part by resistor, light deflection means having reflection part for reflecting light, and frequency of pulse current for driving the light deflection means And a control means for synchronizing the resonance frequency of the shape memory alloy thin film with a resonance frequency of the shape memory alloy thin film.

This configuration corresponds to FIG. 12, and in detail, the above-mentioned control means comprises an optical sensor consisting of a line sensor or PSD, an arithmetic circuit, a waveform generating circuit and an amplifier. In such a mode, the licensor or PS
The optical sensor D detects the vibration displacement of the SMA light deflector, which is the light changing means, detects the position of the center of the displacement amplitude and the displacement amplitude from the signal, and the arithmetic circuit detects the resonance frequency of the SMA light deflector. Then, the position of the central portion of the displacement amplitude is brought to a predetermined position, and the drive pulse is controlled so as to be synchronized with the resonance frequency of the SMA optical deflector. Therefore, SM
The amplitude of the vibration displacement of the A light deflector can be made large. (2) The shape memory alloy thin film as described in (1) above, wherein the control means drives the frequency of the pulse current at a positive frequency that is an integer fraction of the resonance frequency of the light deflection means. Optical deflector using.

This configuration corresponds to FIG. 12 and FIG. 19, and more specifically, the drive frequency of the current pulse for driving the SMA light deflecting unit which is the light changing unit is set to a frequency which is a positive integer fraction of the resonance frequency. In such a mode, the resonance state of the SMA light deflector can be maintained. Therefore, it is possible to drive at a low frequency while keeping the displacement amplitude of the SMA light deflector large. (3) The duty ratio of the pulse current supplied to the light input unit and the output unit, the heat generating unit made of the resistor, the light deflecting unit having the reflecting unit for reflecting the light, and the light deflecting unit is set within a predetermined range. And a control means for controlling the discharge time to be longer than the heating time of the heat generating part, and at least the shape memory alloy thin film is provided in the heat generating part of the resistor. Optical deflector used.

This configuration corresponds to FIG. 12 in detail, and the duty ratio of the current pulse for driving the light deflecting means is set to 8 to.
The range is 12%. In such an aspect, the SMA
The heat radiation time is set longer than the heating time of the light deflector. Therefore, the displacement amplitude of the SMA light deflector can be increased. (4) Input and output parts of current, shape memory alloy thin film part which is heated and cooled by the change of the current and displaces in two directions, and light whose light reflection direction is changed by the displacement of the shape memory alloy thin film part. Optical deflecting means having a reflecting portion, driving means for applying a pulse current through the input / output portion of the optical deflecting means, an optical sensor for detecting an oscillating displacement of the optical deflecting means, and a detection signal of the optical sensor A resonance frequency detecting means for obtaining a vibration frequency based on the natural vibration of the light deflecting means, and a resonance frequency for setting the resonance frequency obtained by the resonance frequency detecting means as a driving frequency of a pulse current applied to the light deflecting means by the driving means. An optical deflector using a shape memory alloy thin film, comprising: setting means.

This configuration corresponds to S1 and S2 in FIG. In such a mode, the resonance frequency detecting means S1 finds the vibration frequency of the free deflecting state of the light deflecting means, and the resonance frequency setting means S2 determines the natural vibration frequency of the light deflecting means as the driving frequency of the driving means. It becomes possible to automatically set, and the amplitude of the vibration displacement of the light deflecting means can be increased by the resonance. (5) In the optical deflector according to (4) above, the resonance frequency detecting means applies a pulse current to the optical deflecting means by the driving means and superimposes a minute vibration on a detection signal from the optical sensor. An optical deflector using a shape memory alloy thin film, which is for determining the vibration frequency of a.

This configuration corresponds to S1 and S2 in FIG. In such an aspect, the resonance frequency of the optical deflecting means is easily obtained by detecting the micro-vibration based on the natural vibration of the optical deflecting means caused by the pulse current application by the optical sensor to obtain the vibration frequency by the resonance frequency detecting means S1. The amplitude of the vibration displacement can be increased by setting the resonance frequency in the drive means by the resonance frequency setting means S2. (6) In the optical deflector according to (4) or (5), further, drive means is provided so as to receive a detection signal from the optical sensor and detect the midpoint of the vibration displacement at a predetermined position of the optical sensor. An optical deflector using a shape memory alloy thin film, comprising: an amplitude adjusting means for automatically adjusting the amplitude of a pulse current applied by the device.

This configuration corresponds to S1 to S5 in FIG. In such a mode, further, the amplitude adjusting means S3 to S5 further automatically adjust the amplitude of the applied pulse current so that the midpoint of the vibration displacement of the optical deflecting means can be detected at a predetermined position of the optical sensor. The position of the midpoint of the vibration displacement can be maintained at a fixed position, and the optical deflection at the resonance frequency can be stably maintained. (7) In the optical deflector described in (6) above,
An optical deflector using a shape memory alloy thin film, comprising a duty ratio adjusting means for automatically adjusting a duty ratio of a pulse current applied by a driving means so that the vibration amplitude of the light deflecting means has a maximum value. .

This configuration corresponds to S1 to S6 in FIG. In such a mode, further, the duty ratio adjusting means S6 automatically adjusts the duty ratio of the input pulse current, whereby the amplitude of the displacement vibration can be maintained at the maximum value. (8) In the optical deflector according to (4), (5), (6) or (7), the detection signal from the optical sensor is further received and the maximum amplitude of displacement vibration by the optical deflecting means is obtained. Amplitude change detection means for detecting the amount of decrease in vibration amplitude, and drive frequency automatic adjustment means for automatically adjusting the drive frequency of the applied current pulse by the drive means in response to the detection of decrease in vibration amplitude by the amplitude change detection means. An optical deflector using a shape memory alloy thin film.

This configuration corresponds to S1 to S12 in FIG. In such a mode, the drive frequency automatic adjusting means S8 to S1 are further based on the detection of the decrease in the vibration amplitude of the light deflecting means by the amplitude change detecting means S7.
By automatically adjusting the drive frequency in accordance with the change in the amplitude according to 2, the resonance state can be maintained by following the change in the resonance frequency due to the temperature change or the like. (9) An optical deflector having a current input part and an output part, a heat generating part by a resistor, and a reflecting part for reflecting light,
In the control of the deflection angle of the optical deflector using the shape memory alloy thin film, which is characterized in that at least the heat-generating portion of the resistor is provided with the shape memory alloy thin film, when the maximum deflection angle is obtained, drive at the resonance frequency. A method for controlling an optical deflector using a shape memory alloy thin film, which is characterized by driving at a frequency deviated from a resonance frequency when a small deflection angle is obtained.

Such a method corresponds to FIG. 12, and in detail, the displacement detection of the SMA light deflecting section which is the light deflecting means is detected,
Based on the displacement detection signal, resonance frequency, median displacement amplitude,
The displacement amplitude is detected, and the frequency of the current pulse that drives the SMA light deflector is varied.

With such a method, the frequency of the current pulse for driving the SMA light deflector is changed. Therefore, the displacement amplitude of the SMA light deflector can be changed. (10) Light deflection means having a current input portion and a current output portion, a heating portion formed of a resistor, and a reflection portion for reflecting light, and an amplitude of a voltage for driving the light deflection means or an offset of a driving voltage. An optical deflector using a shape memory alloy thin film, comprising: a control unit that adjusts at least one of the voltages, and a shape memory alloy thin film is provided at least in a heating portion of the resistor.

This mode corresponds to FIG. 20, and when the temperature of the SMA light deflecting section rises due to the rise of the environment temperature, the amplitude of the driving voltage is reduced, and conversely, the environment temperature falls or the SMA light deflecting section is influenced by the wind. When the temperature of the part drops, the amplitude of the drive voltage is increased or the offset voltage is superimposed. Therefore, the operation of the SMA light deflector can be driven under the condition that the displacement amplitude is large. (11) A shape memory alloy thin film is provided, which has a light deflecting unit composed of a current input part and an output part, a heat generating part made of a resistor, and a reflecting part reflecting light. And a cover member for covering the light deflector, wherein at least a portion of the cover member through which light of the light deflector is formed is a transparent member.

This mode corresponds to FIG. 21, and shields the SMA light deflector from the external environment. Therefore, the temperature change of the environment where the SMA light deflector is placed is suppressed small, and the fluctuation of the mechanical operating point of the SMA light deflector and the fluctuation of the resonance frequency are suppressed small.

[0081]

As described in detail above, according to the present invention,
It is possible to provide an optical deflector using a shape memory alloy thin film that maintains a stable resonance state even if the ambient temperature changes.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical deflector using an SMA thin film according to a first embodiment.

2 (a) to (c) are plane patterns, and (d) to (f) are cross-sections AA 'and B- in (a) to (c).
It is a figure which shows the mode of B'and CC '.

FIG. 3 is a diagram showing a differential scanning calorimetry curve of a sample obtained by subjecting a 20 μm-thick SMA to a heat treatment of a crystallization treatment and a shape memory treatment.

FIG. 4 is a diagram showing a configuration of a measurement system for examining a vibration characteristic of an SMA light deflector.

FIG. 5 is a diagram showing a bending displacement of the SMA light deflector 41 which occurs when a pulse current is applied to the SMA light deflector 41.

FIG. 6 is a diagram showing a relationship between drive current, temperature, and displacement.

7 is a 7 μm thick SMA using the measurement system shown in FIG.
It is a figure which shows the bending displacement characteristic at the time of the pulse drive of the light deflection part 41 formed of a thin film.

FIG. 8A is a diagram showing the relationship between the drive frequency of the 12 μm thick SMA light deflector and the displacement meter output, and FIG. 8B is a diagram showing the relationship of the displacement meter output with respect to the duty ratio (pulse width) of the drive pulse.

FIG. 9A is a diagram showing the relationship between the drive frequency of a 20 μm thick SMA light deflector and the displacement meter output, and FIG. 9B is a diagram showing the relationship of the displacement meter output with respect to the duty ratio (pulse width) of the drive pulse.

FIG. 10 is a diagram showing the relationship between the resonance frequency fR and the film thickness obtained from FIGS. 7 to 9 in the SMA light deflector having a thickness of 7, 12, 20 μm.

FIG. 11 is a diagram showing a relationship between a drive frequency and a vibration amplitude in a 20 μm-thick SMA light deflector.

FIG. 12 is a block diagram showing a first embodiment of the present invention for preventing the SMA light deflector from changing mechanical operating conditions due to the influence of environmental temperature or wind.

13 is a diagram for explaining displacement detection of the SMA light deflector 81. FIG.

14A to 14C are first to fourth displacement detection methods of an SMA light deflector.
It is a figure which shows the modification of.

FIG. 15 is a flowchart for explaining the function of the arithmetic circuit 83 of FIG. 12 as a second embodiment.

16 (a) is a diagram showing an offset voltage, FIG. 16 (b) is a pulse voltage, and FIG. 16 (c) is a diagram showing a drive voltage obtained by adding together (a) and (b).

FIG. 17 is a diagram showing the drive frequency dependency of the displacement meter output (displacement amplitude) when the 7 μm thick SMA light deflector 41 is driven with a duty ratio of 10% and a drive pulse current of 0.455 A.

FIG. 18 is a diagram showing the drive frequency dependency of the displacement meter output (displacement amplitude) when the 7 μm thick SMA light deflector 41 is driven with a duty ratio of 10% and a drive pulse current of 0.455 A.

FIG. 19 is a diagram showing the output of the laser displacement meter when pulse-driven at a cycle of an integer fraction of the resonance frequency of the 20 μm-thick SMA light deflector 41.

FIG. 20 is a diagram showing an example of detecting displacement vibration of the SMA light deflector 151.

FIG. 21 is a diagram showing a third embodiment of the present invention for solving the problem that the mechanical operating point of the SMA light deflector 201 changes due to the influence of ambient temperature and wind.

[Explanation of symbols]

1 ... SMA light deflector, 2, 3 ... Contact pad, 4 ...
Lead wire, 5 ... Resistor, 6 ... Function generator, 7 ... Amplifier, 8, 9 ... Output terminal, 10, 11 ... Lead wire, 12 ... Current, 13, 14 ... Bent portion, 15 ... Laser diode, 16 ... Output light , 17 ... Light reflecting surface, 18 ... Reflected light, 19 ... Bar code.

Claims (3)

[Claims] 1. An optical deflector having a current input part and an output part, a heat generating part made of a resistor, and a reflecting part for reflecting light, and a frequency of a pulse current for driving the light deflecting device. Control means for synchronizing with the resonance frequency of the deflection means,
An optical deflector using a shape memory alloy thin film, comprising a shape memory alloy thin film in at least a heating portion of the resistor. 2. An input / output unit of electric current, a heating unit made of a resistor, an optical deflecting unit having a reflecting unit for reflecting light, and a duty ratio of a pulse current supplied to the optical deflecting unit within a predetermined range. And a control means for controlling the discharge time to be longer than the heating time of the heat generating part, and the shape memory alloy thin film is provided at least in the heat generating part of the resistor. Optical deflector using thin film. 3. An optical deflector having a current input part and an output part, a heat generating part by a resistor, a reflecting part for reflecting light, and a pulse current of the optical deflecting device for adjusting the pulse current of the optical deflecting device. An optical deflector using a shape memory alloy thin film, comprising: a control means for controlling a deflection angle to be maximum; and a shape memory alloy thin film provided at least in a heat generating portion of the resistor.