JP2017067877A - Biaxial Actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a biaxial actuator for driving a movable part to rotate in two axial directions perpendicular to each other capable of increasing the productivity of the biaxial actuator.SOLUTION: A biaxial actuator 1 drives a movable part to rotate on a first rotation axis S1 and on a second rotation axis S2, which has: a specific frequency f1 of a first specific vibration mode in which the movable part rotates on the first rotation axis S1; a specific frequency f2 of a second specific vibration mode in which the movable part rotates on the second rotation axis S2; and specific frequencies f3, f4 of third and fourth specific vibration modes different from the first and second specific vibration modes. The difference between f3 and f1 is generally equal to the difference between f1 and f4.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a biaxial actuator that rotates a movable part in two orthogonal biaxial directions.

  In recent years, this type of biaxial actuator has been studied for application to a scanning optical system such as a head-up display or a small projector, and has been developed with a MEMS structure that is advantageous for downsizing. In other words, the functional film is formed by sputtering a functional film on a Si substrate and then etching into a predetermined shape. Such a MEMS-structured biaxial actuator is required to have a large amplitude operation and high-precision scanning characteristics.

  An example is shown in FIG. The biaxial actuator 100 is connected to a pair of meander-shaped first vibrating beams 102 each having one end connected to the movable portion 101, and the other ends of the pair of first vibrating beams 102. These first vibrating beams 102 and a first support portion 103 that surrounds the outer periphery of the movable portion 101. A pair of meander-shaped second vibrating beams 104 each connected at one end to the first supporting portion 103 and a second supporting portion 105 connected to the other ends of the pair of second vibrating beams 104 are provided. Yes. Although not particularly shown, the first vibrating beam 102 and the second vibrating beam 104 are provided with a driving film in which a piezoelectric material is disposed between the lower electrode and the upper electrode.

  A drive signal composed of an AC voltage is applied to the drive film of the first vibrating beam 102 to drive the first vibrating beam 102 to resonance. A drive signal having a sawtooth voltage is applied to the drive film of the second vibrating beam 104 to drive the second vibrating beam 104 in a non-resonant manner. By driving the first vibrating beam 102 and the second vibrating beam 104 in this way, the biaxial drive of the movable portion 101 is realized.

  As prior art document information related to the invention of this application, for example, Patent Document 1 is known.

JP 2011-209583 A

  However, in a biaxial actuator having a MEMS structure, variation occurs in thickness control and shape control during processing in film formation and etching of a driving film in the manufacturing process. Due to this variation, the bending stiffness k of the first and second vibrating beams of the biaxial actuator and the amount of moment of inertia I around the rotation axis vary, and therefore, the natural frequency of the biaxial actuator varies in the natural vibration mode. As a result, variation in the swing angle of the movable part occurs in the mass production stage. In order to suppress this variation, the processing accuracy in the MEMS process has to be increased, and it has been difficult to increase productivity.

  Therefore, the present invention aims to solve such problems and increase the productivity of the biaxial actuator.

  In order to achieve this object, the present invention provides a first inherent rotation of a movable part that rotates about a first rotation axis in a biaxial actuator that rotates about a first rotation axis and a second rotation axis. The natural frequency f1 of the vibration mode, the natural frequency f2 of the second natural vibration mode rotating around the second rotation axis, and the third and fourth natural vibrations different from the first and second natural vibration modes. The mode has natural frequencies f3 and f4, and the difference between f3 and f1 is substantially equal to the difference between f1 and f4.

  With this configuration, the productivity of the biaxial actuator can be improved.

The perspective view of the biaxial actuator in Embodiment 1 of this invention Sectional view of the first vibrating beam of the same biaxial actuator Sectional view of the second vibrating beam of the same biaxial actuator Schematic diagram showing the image projection state using the same biaxial actuator The figure which shows the relationship of the natural frequency with respect to the ratio of the bending rigidity of the 2nd drive beam and the amount of moment of inertia in the same biaxial actuator The figure which shows the relationship of the deflection angle with respect to the ratio of the bending rigidity of the 2nd drive beam and the amount of moment of inertia in the biaxial actuator book. A perspective view of a conventional biaxial actuator

  Hereinafter, a biaxial actuator according to an embodiment of the present invention will be described with reference to the drawings.

  In the biaxial actuator 1 shown in FIG. 1, the opposite end portions of the movable portion 2 located at the center portion are connected to the first support portion 4 having a rectangular frame shape via the first vibrating beam 3. Opposing end portions of the first support portion 4 are connected to the rectangular frame-shaped second support portion 6 via the second vibrating beams 5, respectively. A driving film 7 made of a piezoelectric material is formed on the second vibrating beam 5 and the first vibrating beam 3. This drive film 7 is obtained by interposing a piezoelectric layer 10 between a lower electrode 9 and an upper electrode 11, which will be described later. By applying a drive signal between the upper electrode 11 and the lower electrode 9, The driving film 7 expands and contracts due to the inverse piezoelectric effect, and the first vibrating beam 3 and the second vibrating beam 5 can be vibrated.

  And this biaxial actuator 1 vibrates the 1st vibrating beam 3, the movable part 2 rotates around the 1st rotation axis S1, and vibrates the 2nd vibrating beam 5, and the movable part 2 is made into 1st. It rotates around the two rotation axis S2.

  A sawtooth voltage is applied as a drive signal to the drive film 7 provided on the second vibrating beam 5, and the second vibrating beam 5 is vibrated at low speed by non-resonant driving. In addition, a sinusoidal waveform voltage is applied as a drive signal to the drive film 7 provided on the first vibrating beam 3, and the first vibrating beam 3 is rotated at high speed by resonance driving. By combining these vibrations, the movable part 2 can be rotated about two axes of the first rotation axis S1 and the second rotation axis S2 orthogonal to each other.

  The first vibrating beam 3 has a meander shape in which a plurality of linear portions and folded portions are combined so as to meander. As shown in FIG. 2, the drive film 7 is disposed on the Si oxide film 8 formed on the SOI substrate 19, and the lower electrode 9 and the piezoelectric layer are formed from the Si oxide film 8 side. 10 and a stacked structure in which the upper electrodes 11 are sequentially stacked. In addition, as shown in FIG. 1, the drive film 7 is arranged with respect to a plurality of linear portions arranged side by side, and the drive film 7 is disposed between the linear portions where the drive film 7 is provided. The connection wiring 20 is arranged. The difference between the drive film 7 and the connection wiring 20 is that the line of the upper electrode 11 functions as the drive film 7 by setting the line width of the upper electrode 11 provided on the piezoelectric layer 10 wider as shown in FIG. It functions as the connection wiring 20 by setting the width narrow.

  Similar to the first vibrating beam 3, the second vibrating beam 5 has a meander shape in which a plurality of linear portions and folded portions are combined so as to meander. However, as shown in FIG. 3, the straight portion is a laminated structure in which the inorganic layer 14 and the organic layer 13 are stacked as a base 21, and the driving film 7 is disposed on the surface of the base 21. From the side, an upper electrode 11, a piezoelectric layer 10, and a lower electrode 9 are formed in a stacked structure in this order. Although the folded portion is not particularly illustrated, the Si oxide film 8 and the SOI substrate 19 are arranged under the lower electrode 9 in the same manner as the straight line portion in FIG.

  An application example of such a biaxial actuator 1 will be described. FIG. 4 shows an optical scanning device that scans a screen 18 with a laser beam 16 emitted from a light source 15. The biaxial actuator 1 is disposed in the optical path of the laser beam 16 from the light source 15 to the screen 18. Moreover, the reflection angle of the reflected light 17 can be controlled by making the surface of the movable part 2 shown in FIG. 1 into a reflective surface. By rotating the movable portion 2 in the biaxial direction, the reflected light 17 can be scanned on the screen 18 in the biaxial direction, which can be utilized for a laser projector, a head-up display, a head mounted display, and the like.

  However, in such a biaxial actuator 1 having a MEMS structure, when the first vibrating beam 3, the second vibrating beam 5, and the driving film 7 are processed, variations in shape and film thickness occur, and the first vibrating beam 3 and the second vibrating beam 3 The bending stiffness k and the moment of inertia I of the vibrating beam 5 vary. As a result, the natural frequency of the natural vibration mode for causing the movable part 2 to vibrate about the two axes of the first rotation axis S1 and the second rotation axis S2 varies, and the deflection angle of the movable part 2 varies. In addition, since the 2nd vibrating beam 5 is a laminated structure of the inorganic layer 14 and the organic layer 13 as shown in FIG. 3, the dispersion | variation in a shape and film thickness become remarkable.

  Then, in order to solve the variation in the swing angle of the movable portion 2, the biaxial actuator 1 was subjected to vibration analysis using vibration analysis software (COVENTORWARE (registered trademark) 2012 manufactured by Coventer). As a result, the natural vibration mode of the biaxial actuator 1 whose natural frequency varies depending on the ratio of the bending rigidity k of the second vibrating beam 5 and the moment of inertia I of the second vibrating beam 5, or its higher-order natural vibration mode. Then, it has been found that the natural vibration mode of the biaxial actuator 1 in which the movable part rotates around the first rotation axis S1 excites each other, and the swing angle of the movable part 2 attenuates.

The details will be described with reference to FIG. FIG. 5 shows a vibration analysis result by the above-described vibration analysis software, and the horizontal axis represents the square root of the ratio of the bending stiffness k of the second vibrating beam 5 to the amount of inertia I of the second vibrating beam 5 (hereinafter referred to as the following). (Referred to as (k / I) ^1/2 ), and the vertical axis represents the frequency. In FIG. 5, the solid line A indicates the transition of the natural frequency with respect to (k / I) ^1/2 in the natural vibration mode in which the movable portion 2 vibrates around the first rotation axis S1. A broken line B, a broken line C, and a broken line D show transitions of the natural frequency of the unnecessary vibration mode excited by the second vibrating beam 5 with the driving of the first vibrating beam 3 with respect to (k / I) ^{1/2, respectively} . And fluctuates according to (k / I) ^1/2 . That is, the natural resonance modes indicated by the broken lines B, C, and D show transitions having different slopes from the natural resonance mode indicated by the solid line A having a constant frequency and the natural vibration mode that rotates about the second rotation axis S2. .

In the natural vibration mode indicated by the solid line A, the natural resonance frequency fluctuates due to mutual interference in a region close to other natural resonance modes such as the broken line B and the broken line C. However, in the absence of these mutual excitations, there is no frequency fluctuation corresponding to the fluctuation of (k / I) ^1/2 and it is constant. Further, the natural vibration mode in which the movable portion 2 is rotated about the second rotation axis S2 is not shown in FIG. 5 because the natural vibration frequency is as low as 500 to 600 Hz.

Although the horizontal axis of FIG. 5 is (k / I) ^1/2 of the second vibrating beam 5, the natural vibration of the second natural vibration mode in which the movable portion 2 rotates about the second rotation axis S2. Since the frequency is expressed by Equation 1, the same result can be obtained even if expressed as the natural frequency of the second natural vibration mode.

  And since the natural vibration mode shown with the broken line B, C, D has inclination with respect to the natural vibration mode shown with the continuous line A, the part where the solid line A and the broken lines B, C, D cross | intersect arises. As described above, the mutual excitation of the intersecting natural vibration modes becomes significant in the intersecting portion and the vicinity region. It is considered that this phenomenon occurs because the first vibrating beam 3 and the second vibrating beam 5 in the biaxial actuator 1 are connected via the first support portion 4. That is, when the first vibrating beam 3 vibrates at 28 kHz, the second vibrating beam 5 connected to the first vibrating beam 3 via the first support portion 4 has a vibration of 28 kHz in the first vibrating beam 3. Communicated. When the second vibration beam 5 has a natural vibration mode that vibrates in the vicinity of 28 kHz, the vibration of the second vibration beam 5 is not a forced vibration but a free vibration, and the influence of mutual excitation of each natural vibration mode is present. Arise.

The influence of this mutual excitation will be described with reference to FIG. FIG. 6 shows the movable portion 2 in the section (from (k1 / I1) ^1/2 to (k5 / I5) ^1/2 ) from the intersection α of the solid line A and the broken line B to the intersection β of the solid line A and the broken line C shown in FIG. It shows the transition of the deflection angle. Note that the intersection in the α and becomes (k1 / I1) ^1/2 and the intersection β become (k5 / I5) ^1/2 intermediate position (k3 / I3) ^1/2, the natural resonant frequency of the solid line A in FIG. 5 f1 And the difference between the natural resonance frequency f3 of the broken line B and the difference between the natural resonance frequency f1 of the solid line A and the natural resonance frequency f4 of the broken line C are equal. That is, the influence of the mutual excitation between the solid line A and the broken line B and the mutual excitation between the solid line A and the broken line C is minimized, and the swing angle of the movable part 2 is maximized as shown in FIG. Since the influence of mutual excitation increases at the intersection point α and the intersection point β, the deflection angle becomes smaller, and the deflection angle of the movable part 2 becomes the minimum at the intersection point α and the intersection point β. Therefore, the values of the bending stiffness k and the moment of inertia I of the second vibrating beam 5 are set to k3 and I3 where (k / I) ^1/2 in FIG. 5 is an intermediate position between the intersection α and the intersection β. Thus, the amplitude of the biaxial actuator 1 can be maximized. At the intermediate position (k3 / I3) ^1/2 , there are no intersections with other vibration modes between f3 and f1 and between f1 and f4. That is, the broken line B and the broken line C are adjacent to each other, and there is no other unnecessary vibration mode that is inclined with respect to the solid line A between them.

  Further, as described with reference to FIG. 3, the biaxial actuator 1 has the organic layer 13 and the inorganic layer 14 as the base portion 21 of the second vibrating beam 5 in order to ensure a sufficient amount of displacement of the second vibrating beam 5. The laminated structure which has is employ | adopted. When realizing this laminated structure, first, as shown in FIG. 2, the Si oxide film 8, the lower electrode 9, the piezoelectric layer 10, and the upper electrode 11 are formed on the SOI substrate 19. Thereafter, as shown in FIG. 3, an organic layer 13 is formed on the upper electrode 11 by spin coating, and an inorganic layer 14 is provided on the organic layer 13 by plating. Thereafter, the SOI substrate 19 and the Si oxide film 8 can be removed by etching. However, since the second vibrating beam 5 formed by such a process has a large processing variation due to the forming process as described above, the bending stiffness k and the moment of inertia I of the second vibrating beam 5 also vary. It's easy to do. In such a structure with many variations, it is effective to set the bending stiffness k and the moment of inertia I of the second vibrating beam 5 and define the frequency of each natural vibration mode as described above.

  That is, in the manufacturing process of the MEMS structure as described above, the second vibrating beam 5 in which the deflection angle of the movable part 2 is maximized even if the processing variation or film thickness variation of the first vibrating beam 3 or the second vibrating beam 5 occurs. Since the bending stiffness k and the moment of inertia I are set, a margin of the deflection angle of the movable part 2 with respect to machining variations is ensured. As a result, the productivity of the biaxial actuator 1 in the mass production process is increased.

  Note that, at the intermediate positions of the intersections α and β in FIG. 5 described above, the difference between the natural resonance frequency of the solid line A and the natural resonance frequency of the broken line B and the difference between the natural resonance frequency of the solid line A and the natural resonance frequency of the broken line C are equal. Although described as a thing, in practice, the attenuation factor of the movable part 2 indicated by the right axis in FIG. 7 (the degree of deterioration of the deflection angle based on the peak of the deflection angle indicated by the right axis in FIG. 6) is 25%. Anything above is sufficient. Therefore, the range in which the difference between f3 and f1 in the present invention is equal to the difference between f1 and f4 is 3/5 <(f3-f1) / (f1-f4) <5/3 where the attenuation factor is 25% or more. Means the range.

  Further, the second vibrating beam 5 has a laminated structure of the organic layer 13 and the inorganic layer 14 as the base 21, but the Si oxide film 8 is formed on the SOI substrate 19 similar to the first vibrating beam 3 shown in FIG. The effect can be obtained even if the base 21 is provided. Regarding this point, since there are variations in processing dimensions due to side etching or overetching of the side wall during Si processing, it is effective to set the natural frequency of each natural vibration mode within a specified range. In other words, the second vibrating beam 5 is not limited to the structure of the laminated diaphragm of the organic layer 13 and the inorganic layer 14, and the second vibrating beam 5 may be a laminated structure using two or more layers having different elements. good.

  In the present embodiment, a meander structure is used for the second vibrating beam 5 in order to realize a large displacement of the movable part 2 in the biaxial actuator 1. In FIG. 6, the natural vibration modes represented by broken lines B, C, and D are broken lines B, C, and D because the vibration form increases as the second vibrating beam 5 has a more complex structure such as a meander shape. The number of occurrences of the natural vibration mode that represents the transition of the natural frequency increases. Therefore, the setting of the bending stiffness k and the moment of inertia I of the second vibrating beam 5 described above is particularly effective in the meander shape having a complicated structure of the second vibrating beam 5.

  In setting the bending stiffness k and the moment of inertia I of the second vibrating beam 5, it can be adjusted by changing the thickness of the second vibrating beam 5. In particular, the folded portion of the second vibrating beam 5 has a structure in which the Si oxide film 8 and the SOI substrate 19 are laminated on the configuration of the straight portion, and adjusting the thickness of the folded portion is effective for adjusting the amount of inertia I. It is.

  Further, in the case of a structure in which a laminated structure of the organic layer 13 and the inorganic layer 14 is used as the base portion 21 as in the straight line portion shown in FIG. It becomes easy to adjust the stiffness k and the moment of inertia I. This is because if Ni is used as a member of the inorganic layer 14, there are Ni containing a large amount of S (sulfur component) and Ni containing no S component, and the inorganic layer 14 can have a laminated structure. As a result, the Ni layer containing a large amount of the S component can be selectively etched by using the ammonium persulfate aqueous solution as the etchant and the Ni layer not containing the S component using the iron (III) chloride aqueous solution as the etchant. . By this selective etching, the film thickness of the inorganic layer 14 can be easily adjusted with high accuracy, and the bending rigidity k and the moment of inertia I of the second vibrating beam 5 can be easily adjusted.

  INDUSTRIAL APPLICABILITY The present invention can improve productivity in a MEMS process in a biaxial actuator that rotates a movable part in biaxial directions, and is effective in applications of scanning optical systems such as small projectors and head-up displays. is there.

DESCRIPTION OF SYMBOLS 1 Biaxial actuator 2 Movable part 3 1st vibration beam 4 1st support part 5 2nd vibration beam 6 2nd support part S1 1st rotation axis (high frequency drive axis)
S2 Second rotation axis (low frequency drive axis)

Claims (4)

Moving parts;
A first vibrating beam having one end connected to the movable portion and exciting a first natural vibration mode in which the movable portion rotates about a first rotation axis;
A first support connected to the other end of the first vibrating beam;
A second vibrating beam configured to excite a second natural vibration mode in which one end is connected to the first support portion and the movable portion rotates about a second rotation axis orthogonal to the first rotation axis;
In the biaxial actuator provided with the second support portion connected to the other end of the second vibrating beam,
The biaxial actuator has third and fourth natural vibration modes in which the second vibration beam vibrates, which is different from the second natural vibration mode,
The natural frequency of the biaxial actuator that excites the first natural vibration mode is f1,
The natural frequency of the biaxial actuator that excites the second natural vibration mode is f2,
F3, the natural frequency of the biaxial actuator that excites the third natural vibration mode,
The natural frequency of the biaxial actuator that excites the fourth natural vibration mode is f4,
The f3 and the f4 vary according to the ratio of the bending stiffness k around the second rotation axis and the moment of inertia I in the second vibrating beam that defines the f2.
A biaxial actuator in which f1 exists between f3 and f4, and the difference between f3 and f1 is substantially equal to the difference between f1 and f4. 2. The biaxial actuator according to claim 1, wherein the second vibrating beam is a laminated structure in which a plurality of layers having different compositions are stacked in a thickness direction. The biaxial actuator according to claim 1, wherein the second vibrating beam has a meander shape. The biaxial actuator according to claim 1, wherein a difference between f3 and f1 and a difference between f1 and f4 are made substantially equal by adjusting a thickness of the first vibrating beam or the second vibrating beam.

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