Patent Publication Number: US-2021173201-A1

Title: Optical reflective element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. continuation application of PCT International Patent Application Number PCT/JP2019/032338 filed on Aug. 20, 2019, claiming the benefit of priority of Japanese Patent Application Number 2018-162854 filed on Aug. 31, 2018, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an optical reflective element that causes an illumination position of laser light etc. to reciprocate. 
     2. Description of the Related Art 
     Conventional optical reflective elements that cause an illumination position of laser light to reciprocate include, as exemplified in Japanese Unexamined Patent Application Publication No. 2009-244602, a reflective body that reflects laser light etc., a connector body that is connected with the reflective body and causes the reflective body to rotationally oscillate by the connector body being twisted, vibration bodies in the shape of two arms which extend in the direction intersecting the rotational axis of the reflective body for causing the connector body to generate reciprocal torsion, and driving bodies each including a piezoelectric element etc. for causing respective vibration bodies to vibrate. 
     SUMMARY 
     Such optical reflective elements are smaller and lighter than reflective elements in which a polygon mirror is caused to rotate by a motor, and also use less electric power to cause the reflective bodies to rotationally oscillate. However, when such an optical reflective element is attached to, for example, a car which produces strong vibrations, a disturbance vibration is transmitted to the reflective body and prevent the optical reflective element from driving stably. 
     In view of the above, the present disclosure aims to provide a highly durable optical reflective element that can be stably driven even when a disturbance vibration is produced. 
     In order to provide such an optical reflective element, an optical reflective element according to an aspect of the present disclosure includes: a reflective body that rotationally oscillates about a first rotational axis, and reflects light; a first connector body that is disposed along the first rotational axis, and includes a distal end portion coupled to the reflective body and a groove portion provided in a position in which the first rotational axis is located; a first vibration body that extends in a direction intersecting the first rotational axis, and is coupled to a proximal end portion of the first connector body; a second vibration body that extends in a direction intersecting the first rotational axis, and is coupled to the proximal end portion of the first connector body, the second vibration body being on a side opposite the first vibration body with respect to the first rotational axis; a first driving body that is coupled to a distal end portion of the first vibration body, and causes the first connector body to rotationally oscillate via the first vibration body; a second driving body that is coupled to a distal end portion of the second vibration body, and causes the first connector body to rotationally oscillate via the second vibration body; a first base; and a second connector body that connects the first vibration body and the second vibration body to the first base in a manner that allows the first vibration body and the second vibration body to vibrate. 
     According to the present disclosure, it is possible to provide a highly durable optical reflective element that can be stably driven even when a disturbance vibration is produced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG. 1  is a plan view illustrating an optical reflective element according to Embodiment 1; 
         FIG. 2  is a perspective view illustrating the optical reflective element according to Embodiment 1; 
         FIG. 3  is a plan view illustrating an optical reflective element according to Variation 1; 
         FIG. 4  is a perspective view illustrating an optical reflective element according to Variation 2; 
         FIG. 5  is a sectional view illustrating a first connector body from a longitudinal direction; 
         FIG. 6  is a plan view illustrating an optical reflective element according to Variation 3; 
         FIG. 7  is a plan view illustrating an optical reflective element according to Embodiment 2; 
         FIG. 8  is a plan view illustrating an optical reflective element according to Embodiment 3; and 
         FIG. 9  is a perspective view illustrating an optical reflective element according to another variation. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Next, embodiments of an optical reflective element according to the present disclosure will be described with reference to the drawings. Note that the embodiments below each describe a general or specific example. The numerical values, shapes, materials, structural elements, the arrangement and connection of the structural elements, steps, and processing orders of the steps, etc. presented in the embodiments below are mere examples and do not limit the present disclosure. Furthermore, among the structural elements in the embodiments below, those not recited in any one of the independent claims representing the most generic concepts will be described as optional structural elements. 
     In addition, the drawings are schematically illustrated. The structural elements in these schematic diagrams are optionally emphasized, omitted, and proportionally adjusted to describe the present disclosure. For this reason, the structural elements may have shapes, positional relations, and proportions which are different from the actual shapes, positional relations, and proportions. 
     Embodiment 1 
       FIG. 1  is a plan view illustrating an optical reflective element according to Embodiment 1.  FIG. 2  is a perspective view illustrating the optical reflective element according to Embodiment 1. 
     Optical reflective element  100  is a device that periodically changes the angle of reflection of light, such as laser light, and periodically sweeps an illumination position of the light. As illustrated in  FIG. 1  and  FIG. 2 , optical reflective element  100  includes: reflective body  110 ; first connector body  121  and second connector body  122  which are connector bodies; first vibration body  141  and second vibration body  142  which are vibration bodies; first driving body  151  and second driving body  152  which are driving bodies; and first base  161  which is a base. In addition, in this embodiment, part of reflective body  110 , the connector bodies, part of the vibration bodies, and the base are integrally formed by removing unnecessary portions from one base material. Specifically, the unnecessary portions are removed from a silicon substrate using an etching technique employed in a semiconductor manufacturing process to integrally form part of reflective body  110 , the connector bodies, part of the vibration bodies, and the base. Optical reflective element  100  is the so-called micro electro mechanical systems (MEMS). Moreover, optical reflective element  100  includes first monitor element  171  and second monitor element  172  which are monitor elements. 
     Here, although a material that the base material includes is not particularly limited, it is desirable that the material has mechanical strength and a high Young&#39;s modulus, such as metals, crystals, glass, and resins. Specifically, the material may be metals and alloys, such as silicon, titanium, stainless steel, elinvar, and a brass alloy. The use of such metals and alloys makes it possible to realize optical reflective element  100  having an excellent vibration characteristic and excellent processability. 
     Reflective body  110  is a part that rotationally oscillates (repetitive rotational vibration) about first rotational axis  101 , and reflects light. Although the shape of reflective body  110  is not particularly limited, reflective body  110  in this embodiment is in the shape of a quadrilateral plate. Reflective body  110  is provided with reflector  111  on its surface which can reflect light to be reflected with high reflectance. The material used for reflector  111  can be optionally selected. For example, the material may be metals or metallic compounds, such as gold, silver, copper, and aluminum. In addition, reflector  111  may consist of two or more layers. Furthermore, reflector  111  may be provided by smoothly polishing a surface of reflective body  110 . Reflector  111  may have a curved surface, instead of a plane surface. 
     First connector body  121  is a member that is disposed along first rotational axis  101 . First connector body  121  holds reflective body  110  in a state in which a distal end portion of first connector body  121  and reflective body  110  are coupled together and a proximal end portion of first connector body  121  and each of a proximal end portion of first vibration body  141  and a proximal end portion of second vibration body  142  are coupled together. First connector body  121  is a member that transmits, to reflective body  110 , torque for causing reflective body  110  to rotationally oscillate. First connector body  121  is capable of causing reflective body  110  to rotationally oscillate by first connector body  121  being twisted about first rotational axis  101  (see θ 1  in the diagram) while holding reflective body  110 . First connector body  121  includes groove portion  150  in a position in which first rotational axis  101  is located. 
     Although the shape of first connector body  121  is not particularly limited, first connector body  121  is in the shape of a slim bar having, as a whole, a width (a length in the X-axis direction in the diagram) narrower than the width of reflective body  110  since first connector body  121  is a member that causes reflective body  110  to rotationally oscillate by first connector body  121  being twisted. In this embodiment, groove portion  150  that is provided in first connector body  121  is in the shape of a slit that penetrates first connector body  121  in the direction (the Z-axis direction in the diagram) orthogonal to a reflective surface of reflective body  110 . In addition, groove portion  150  extends from the distal end portion of first connector body  121  which is connected to reflective body  110  to the proximal end portion of first connector body  121  which is connected to coupling body  149 . Accordingly, first connector body  121  can be seen as two bar-shaped members with first rotational axis  101  interposed therebetween. Cross sections of first connector body  121  perpendicular to first rotational axis  101  each are in the shape of a quadrilateral. The thickness of first connector body  121  is the same as the thickness of reflective body  110  and the other members. The cross sections of first connector body  121  have the same shape from reflective body  110  to the proximal end portion of first vibration body  141  and the proximal end portion of second vibration body  142 . The cross sections of first connector body  121  orthogonal to first rotational axis  101  having the uniform quadrilateral shape and uniform area along first rotational axis  101 , and first connector body  121  being rotationally symmetric with respect to first rotational axis  101  enable the entirety of first connector body  121  to uniformly twist, thereby preventing damage due to a stress concentration in the longitudinal direction of first connector body  121 . 
     In addition, the inventor has found out that stress concentrates on an area in which first rotational axis  101  is located in the case in which groove portion  150  is not provided in first connector body  121 . Accordingly, in this embodiment, groove portion  150  is provided to make a gap in an area in which first rotational axis  101  is located to enable the stress to be distributed to each of separated portions of first connector body  121 . This prevents damage due to a stress concentration in the widthwise direction of first connector body  121 . 
     It should be noted that these structural members need not have the same thickness. For example, if reflective body  110  is thicker than first connector body  121  and a transmission body, it is suitable to prevent surface distortion of reflective body  110 . In addition, if the thickness of first base  161  increases, it is suitable to secure a space in the Z-axis direction which is necessary for driving first driving body  151 , second driving body  152 , and reflective body  110  in the case in which optical reflective element  100  is attached to a flat surface of a product, for example. The increase in the thickness of first base  161  also increases the structural strength of the entirety of optical reflective element  100 . 
     It should be noted that the description of first connector body  121  being disposed along first rotational axis  101  includes not only the case in which first connector body  121  is disposed directly along first rotational axis  101 , but also the case in which first connector body  121  is disposed along the entirety of first rotational axis  101  that is imaginarily straight, even if first connector body  121  windingly bends or zigzags. 
     In addition, the term “intersection” used in this embodiment and the claims includes not only an intersection in which two lines are in contact with each other, but also an overpass crossing or an underpass crossing in which two lines do not contact with each other. 
     The vibration bodies including first vibration body  141  and second vibration body  142  each are a member in the shape of an arm. The vibration bodies vibrate in the circumferential direction about first rotational axis  101  to produce torque for causing reflective body  110  to rotationally oscillate. The vibration bodies each extend in a direction intersecting first rotational axis  101 . First vibration body  141  is disposed in a direction intersecting first rotational axis  101 , and is coupled to the proximal end portion of first connector body  121 . Second vibration body  142  is disposed in a direction intersecting first rotational axis  101  on the side opposite first vibration body  141  with respect to first rotational axis  101 , and is coupled to the proximal end portion of first connector body  121 . 
     In this embodiment, first vibration body  141  is a member in the shape of a quadrilateral bar that extends in a direction orthogonal to first rotational axis  101 , and second vibration body  142  is a member in the shape of a quadrilateral bar that extends in a direction orthogonal to first rotational axis  101  and in a direction opposite to first vibration body  141 . 
     In addition, the proximal end portion of first vibration body  141  and the proximal end portion of second vibration body  142  are integrally coupled together with coupling body  149 . First vibration body  141  and second vibration body  142  are in the shape of a straight bar, and each extend from first rotational axis  101  as their center and in a direction orthogonal to first rotational axis  101 . 
     The driving bodies including first driving body  151  and second driving body  152  are members that produce a driving force for causing distal end portions of the vibration bodies to vibrate in the circumferential direction about first rotational axis  101 . First driving body  151  is coupled to the distal end portion of first vibration body  141 . First driving body  151  is a member that causes first vibration body  141  to vibrate about first rotational axis  101  to cause first connector body  121  to rotationally oscillate. Second driving body  152  is coupled to the distal end portion of second vibration body  142 . Second driving body  152  is a member that causes second vibration body  142  to vibrate about first rotational axis  101  to cause first connector body  121  to rotationally oscillate. 
     In this embodiment, first driving body  151  has a proximal end portion that is integrally coupled to the distal end portion of first vibration body  141 . First driving body  151  includes first driving body main portion  183  having a cross section in the shape of a quadrilateral bar that is disposed along first rotational axis  101  and extends toward reflective body  110 . First driving body main portion  183  includes, on its surface, first piezoelectric element  185  that is a piezoelectric element in the shape of a narrow plate disposed along first rotational axis  101 . The application of a periodically varying voltage to first piezoelectric element  185  causes first piezoelectric element  185  to repeatedly expand and contract. First driving body main portion  183  repeatedly bends and straightens out in accordance with the motion of first piezoelectric element  185 . A distal end portion of first driving body main portion  183  which extends over the proximal end portion of first driving body  151  which is coupled to first vibration body  141  vibrates greatly, and the vibrational energy of the entire first driving body  151  is transmitted to the distal end portion of first vibration body  141 . 
     Like first driving body  151 , second driving body  152  also includes second driving body main portion  184  and second piezoelectric element  186 . Second driving body  152  and first driving body  151  are symmetrically disposed with respect to an imaginary plane in which first rotational axis  101  is located and which is orthogonal to the surface of reflective body  110 . Second driving body  152  has a proximal end portion that is coupled to the distal end portion of second vibration body  142 . In addition, second driving body  152  operates in the same manner as first driving body  151 . 
     In this embodiment, the piezoelectric elements are thin-film stacking-type piezoelectric actuators each having a stacked body structure in which an electrode and a piezoelectric body are stacked in the thickness direction. The piezoelectric elements are formed on the respective surfaces of the driving body main portions. With this, it is possible to make the driving bodies thinner. 
     It should be noted that the driving bodies each may include a member, a device, etc. which generate power using not only the distortion of a piezoelectric element, but also an interaction with a magnetic field and an electric field. The driving bodies each may vibrate by changing at least one of a magnetic field and an electric field which are produced by an external device, or by changing at least one of a self-produced magnetic field and a self-produced electric field. In addition, the piezoelectric bodies may include, for example, a piezoelectric material having a high piezoelectric constant, such as titanic acid lead zirconate (PZT). 
     First base  161  is a member for attaching optical reflective element  100  to an external structural member etc. First base  161  is coupled to second connector body  122  that connects first vibration body  141  and second vibration body  142  to first base  161  in a manner that allows first vibration body  141  and second vibration body  142  to vibrate. 
     Second connector body  122  is disposed along first rotational axis  101 . Second connector body  122  has a proximal end portion coupled to first base  161 , and a distal end portion coupled to the proximal end portion of first vibration body  141  and the proximal end portion of second vibration body  142 . 
     Although the shape of second connector body  122  is not particularly limited, second connector body  122  is in the shape of a bar and has torsional rigidity greater than the torsional rigidity of first connector body  121  since second connector body  122  is a member that tolerates the torsion of first connector body  121  for first base  161  by second connector body  122  being twisted by vibrations transmitted from first vibration body  141  and second vibration body  142 . In this embodiment, cross sections of second connector body  122  perpendicular to first rotational axis  101  each are in the shape of a quadrilateral. The thickness of second connector body  122  is the same as the thickness of first connector body  121  and the other members. Accordingly, second connector body  122  has the width (the length in the X-axis direction in the diagram) greater than the width of first connector body  121 . In addition, the cross sections of second connector body  122  have the same shape from first base  161  to the vibration bodies. This prevents a stress concentration in the same manner as first connector body  121 , thereby preventing second connector body  122  from being fractured. 
     In this embodiment, the entirety of first connector body  121  and second connector body  122  is weak in torsional rigidity since the torsional rigidity of first connector body  121  and second connector body  122  is uniform along first rotational axis  101 . Accordingly, the torsional rigidity per unit length of first connector body  121  is weaker than that of second connector body  122 . It should be noted that if first connector body  121  has a portion that is weaker in torsional rigidity than the torsional rigidity of the remaining portion, and if second connector body  122  has a portion weaker in torsional rigidity than the torsional rigidity of the remaining portion, it is desirable that the torsional rigidity of first connector body  121  is weaker than that of second connector body  122  when those portions having the weakest torsional rigidity are compared. 
     Like first connector body  121 , second connector body  122  may be disposed, not only directly along first rotational axis  101 , but also windingly bended or zigzagged along first rotational axis  101 . Even in such a case, first connector body  121  has weaker torsional rigidity than the torsional rigidity of second connector body  122  when the torsional rigidity about first rotational axis  101  is compared between first connector body  121  and second connector body  122 . 
     In this embodiment, first monitor element  171  and second monitor element  172 , which are the monitor elements, are attached to first vibration body  141  and second vibration body  142 , respectively. The monitor elements detect, as distortion, the bending states of these vibration bodies. The rotational oscillation state of reflective body  110  can be accurately monitored by measuring outputs from the monitor elements. 
     In this embodiment, first monitor element  171  and second monitor element  172  are attached to first vibration body  141  and second vibration body  142 , respectively. Each of these first monitor element  171  and second monitor element  172  is connected to a detection circuit which is not illustrated, and a difference in outputs from the two monitor elements is detected. This cancels various noises, and thus the rotational oscillation state of reflective body  110  can be accurately monitored. Accordingly, it is possible to feed back this accurately monitored rotational oscillation state of reflective body  110  for the control of the driving bodies. 
     In optical reflective element  100  described in the above Embodiment 1, driving of first driving body  151  and second driving body  152  in antiphase causes first vibration body  141  and second vibration body  142  to vibrate in antiphase, thereby producing torque having the same rotational direction about first rotational axis  101 . The transmission of this torque to the proximal end portion of first connector body  121  enables efficient torque transmission. In addition, even if a disturbance vibration is transmitted to optical reflective element  100  via first base  161 , second connector body  122  prevents the transmission of the disturbance vibration to first connector body  121 . This enables reflective body  110  to stably rotationally oscillate. 
     Furthermore, efficient transmission of vibration (torque) that is produced by first vibration body  141  and second vibration body  142  to first connector body  121  enhances a degree of the resonance sharpness (Q factor) of a structural body including reflective body  110  and first connector body  121 . In other words, the degree of the resonance sharpness (Q factor) of the structural body including reflective body  110  and first connector body  121  enhances due to the reduction in transmission loss of the vibration (torque) transmitted to first connector body  121 . The driving frequency band of reflective body  110  narrows as a degree of resonance sharpness (Q factor) enhances. Accordingly, optical reflective element  100  is less likely to be affected by a disturbance vibration, and thus reflective body  110  is allowed to stably rotationally oscillate. 
     In addition, groove portion  150  provided in first connector body  121  is capable of (i) distributing the stress concentrated about first rotational axis  101 , (ii) enhancing the mechanical strength of first connector body  121 , (iii) increasing the movable range (oscillation angle denoted by θ) of optical reflective element  100 , and (iv) enhancing the durability of optical reflective element  100 . 
     It should be noted that the present disclosure is not limited to the above-described embodiment. For example, different embodiments realized by combining optional structural elements described in the present specification or by excluding some of the structural elements described in the present specification may be embodiments of the present disclosure. The present disclosure also includes variations achieved by applying various modifications conceivable to those skilled in the art to each of the embodiments etc., without departing from the essence of the present disclosure, or in other words, without departing from the meaning of wording recited in the claims. 
     For example, as illustrated in  FIG. 3 , second connector body  122  may be divided into parts so as to be coupled to each of the proximal end portion of first vibration body  141  and the proximal end portion of second vibration body  142 . In this case, the torsional rigidity of second connector body  122  about first rotational axis  101  means the rigidity obtained by twisting the entire second connector body  122 . Accordingly, the torsional rigidity can be enhanced structurally by placing several parts of second connector body  122  further apart from one another with first rotational axis  101  interposed therebetween. 
     The torsional rigidity per unit length of second connector body  122  may be higher than that of first connector body  121 . The torsional rigidity per unit length of second connector body  122  may be enhanced by increasing the length (thickness) of second connector body  122  in the direction (the Z-axis direction in the diagram) orthogonal to the reflective surface (the X-Y plane in the diagram) of reflective body  110  as illustrated in  FIG. 4 . 
     The method of making the thickness of second connector body  122  greater than the thickness of first connector body  121  is not particularly limited. For example, reinforcing member  129  may be attached to the surface of second connector body  122  to increase the thickness of second connector body  122 . In addition, the material of reinforcing member  129  is not particularly limited. For example, reinforcing member  129  may include the same material used for the piezoelectric element so that reinforcing member  129  and the piezoelectric element can be formed on second connector body  122  in the same process. 
     Conversely, first connector body  121  may be made thinner than second connector body  122 . For example, first connector body  121  can be made thinner by etching only the surface of first connector body  121 . 
     In addition, even in the case in which first connector body  121  and second connector body  122  have the same shape and the same area in cross sections orthogonal to first rotational axis  101 , first connector body  121  and second connector body  122  may include mutually different materials to make the torsional rigidity per unit length of second connector body  122  higher than that of first connector body  121 . 
     Furthermore, even if first connector body  121  and second connector body  122  include the same material, reformation of the material by heating, such as quenching and annealing, may also make the torsional rigidity per unit length of second connector body  122  higher than that of first connector body  121 . 
     In addition, groove portion  150  need not be in the shape of a slit that penetrates first connector body  121 . Groove portion  150  may be a groove with a closed end as illustrated in  FIG. 5 . In this case, groove portions  150  may be provided, facing in opposite directions, in respective two surfaces of first connector body  121  for improving the symmetry of first connector body  121 . It should be noted that although the cross section of each of the grooves in  FIG. 5  is in the shape of a quadrilateral, the shape is not limited to a quadrilateral. In the cross-sectional view of a groove portion, the closed end of the groove portion may have a curved shape (U shape), a V shape, etc. 
     In addition, as illustrated in  FIG. 6 , lateral groove portion  160  may be provided on both sides of groove portion  150  such that lateral groove portions  160  are rotationally symmetric with respect to first rotational axis  101 . 
     Embodiment 2 
     Next, a different embodiment of an optical reflective element will be described. It should be noted that elements (portions) having effects, functions, shapes, mechanisms, or structures identical to effects, functions, shapes, mechanisms, or structures of the elements (portions) described in Embodiment 1 may be given the same reference numerals, and descriptions of those elements may be omitted. In addition, the following mainly describes points different from Embodiment 1, and the redundant descriptions may be omitted. 
       FIG. 7  is a plan view illustrating an optical reflective element according to Embodiment 2. 
     Optical reflective element  200  according to Embodiment 2 is a device that causes one reflective body  110  to rotationally oscillate by two rotational oscillation mechanisms that are symmetric across an imaginary plane which is orthogonal to first rotational axis  101  and in which the center of reflective body  110  is located. The rotational oscillation mechanisms include respective connector bodies, vibration bodies, driving bodies, bases, and monitor elements which are disposed symmetric across the imaginary plane. In addition, functions and connection modes of the connector bodies, the vibration bodies, the driving bodies, the bases, and the monitor elements included in the rotational oscillation mechanisms are the same as the functions and the connection modes described in Embodiment 1. 
     As specifically illustrated in  FIG. 7 , first rotational oscillation mechanism  201  includes, as connector bodies, first connector body  121  and second connector body  122 , and second rotational oscillation mechanism  202  includes, as connector bodies, third connector body  123  and fourth connector body  124 . First connector body  121  and second connector body  122 , and third connector body  123  and fourth connector body  124  are disposed symmetric across the imaginary plane. Third connector body  123  is disposed opposite first connector body  121  with respect to reflective body  110  and along first rotational axis  101 . Third connector body  123  has a distal end portion that is coupled to reflective body  110 . Like first connector body  121 , third connector body  123  is provided with groove portion  150 . First rotational oscillation mechanism  201  includes, as vibration bodies, first vibration body  141  and second vibration body  142 , and second rotational oscillation mechanism  202  includes, as vibration bodies, third vibration body  143  and fourth vibration body  144 . First vibration body  141  and second vibration body  142 , and third vibration body  143  and fourth vibration body  144  are disposed symmetric across the imaginary plane. First rotational oscillation mechanism  201  includes, as driving bodies, first driving body  151  and second driving body  152 , and second rotational oscillation mechanism  202  includes, as driving bodies, third driving body  153  and fourth driving body  154 . First driving body  151  and second driving body  152 , and third driving body  153  and fourth driving body  154  are disposed symmetric across the imaginary plane. Like first rotational oscillation mechanism  201 , third driving body  153  includes third driving body main portion  187  and third piezoelectric element  189 , and fourth driving body  154  includes fourth driving body main portion  188  and fourth piezoelectric element  190 . First rotational oscillation mechanism  201  includes, as a base, first base  161 , and second rotational oscillation mechanism  202  includes, as a base, second base  162 . First base  161  and second base  162  are disposed symmetric across the imaginary plane. In this embodiment, first base  161  and second base  162  are integrally coupled together, and form a quadrilateral frame member as a whole. In addition, like first rotational oscillation mechanism  201 , second rotational oscillation mechanism  202  includes third vibration body  143  to which third monitor element  173  is attached, and fourth vibration body  144  to which fourth monitor element  174  is attached. 
     In addition to the advantageous effects described in Embodiment 1, optical reflective element  200  according to Embodiment 2 can steady reflective body  110  and can cause reflective body  110  to stably rotationally oscillate about first rotational axis  101 , since torque for rotational oscillation is transmitted along first rotational axis  101  from both sides of reflective body  110 . 
     Furthermore, since the ends of first base  161  and the ends of second base  162  are coupled together to form a frame shape, the structural strength of the entire optical reflective element  200  is enhanced, and thus first connector  121  and second connector  122  are less likely to be affected by a disturbance vibration. This enables reflective body  110  to stably rotationally oscillate. 
     Moreover, since a degree of the resonance sharpness (Q factor) of a structural body including reflective body  110 , first connector body  121 , second connector  122 , third connector  123 , and fourth connector  124  enhances, the driving frequency band of reflective body  110  narrows. Accordingly, optical reflective element  200  is less likely to be affected by a disturbance vibration. This enables reflective body  110  to stably rotationally oscillate. However, first base  161  and second base  162  need not be coupled together. In that case, optical reflective element  200  becomes smaller in the X-axis direction in the diagram, and thus gain advantages in downsizing and cost reduction. 
     Embodiment 3 
     Next, a different embodiment of an optical reflective element will be described. It should be noted that elements (portions) having effects, functions, shapes, mechanisms, or structures identical to effects, functions, shapes, mechanisms, or structures of the elements (portions) described in Embodiment 1 and Embodiment 2 may be given the same reference numerals, and descriptions of those elements may be omitted. In addition, the following mainly describes points different from Embodiment 1 and Embodiment 2, and the redundant descriptions may be omitted. 
       FIG. 8  is a plan view illustrating an optical reflective element according to Embodiment 3. It should be noted that indications of some of reference numerals of first rotational oscillation mechanism  201  and second rotational oscillation mechanism  202  are omitted. 
     Optical reflective element  300  according to Embodiment 3 further includes third rotational oscillation mechanism  203  and fourth rotational oscillation mechanism  204 . Third rotational oscillation mechanism  203  and fourth rotational oscillation mechanism  204  are capable of causing reflective body  110 , first rotational oscillation mechanism  201 , and second rotational oscillation mechanism  202 , which are described in Embodiment 2, to rotationally oscillate as a whole. 
     Third rotational oscillation mechanism  203  is a device that causes reflective body  110 , first rotational oscillation mechanism  201 , and second rotational oscillation mechanism  202  to integrally rotationally oscillate about second rotational axis  102 . Second rotational axis  102  intersects with (in this embodiment, second rotational axis  102  is orthogonal to) first rotational axis  101  about which first rotational oscillation mechanism  201  and second rotational oscillation mechanism  202  cause reflective body  110  to rotationally oscillate. Like first rotational oscillation mechanism  201 , third rotational oscillation mechanism  203  includes a connector body, a vibration body, a driving body, a base, and a monitor element. In addition, functions and connection modes of the connector body, the vibration body, the driving body, the base, and the monitor element are the same as the functions and the connection modes described in Embodiment 2. 
     As specifically illustrated in  FIG. 8 , third rotational oscillation mechanism  203  includes, as connector bodies, fifth connector body  125  and sixth connector body  126 . Fifth connector body  125  is disposed along second rotational axis  102  that passes through reflective body  110 , and has a distal end portion that is coupled to a frame member consisting of first base  161  and second base  162 . Fifth connector body  125  includes groove portion  150  that is provided in a position in which second rotational axis  102  is located. Groove portion  150  that is provided in fifth connector body  125  is in the shape of a slit that penetrates fifth connector body  125  in the direction (the Z-axis direction in the diagram) orthogonal to a reflective surface of reflective body  110 . In addition, groove portion  150  extends from a distal end portion of fifth connector body  125  which is connected to reflective body  110  to a proximal end portion of fifth connector body  125 . Accordingly, fifth connector body  125  can be seen as two bar-shaped members with second rotational axis  102  interposed therebetween. Third rotational oscillation mechanism  203  includes, as vibration bodies, fifth vibration body  145  and sixth vibration body  146 . Third rotational oscillation mechanism  203  includes, as driving bodies, fifth driving body  155  and sixth driving body  156 . Fifth driving body  155  includes fifth driving body main portion  191  and fifth piezoelectric element  192 , and sixth driving body  156  includes sixth driving body main portion  193  and sixth piezoelectric element  194 . Third rotational oscillation mechanism  203  includes, as a base, third base  163 . In this embodiment, third base  163  is a member for attaching optical reflective element  300  to an external structural member, and first base  161  is integrally attached to the distal end portion of fifth connector body  125  of third rotational oscillation mechanism  203 . Like first rotational oscillation mechanism  201  etc., third rotational oscillation mechanism  203  includes fifth vibration body  145  to which fifth monitor element  175  is attached, and sixth vibration body  146  to which sixth monitor element  176  is attached. 
     Fourth rotational oscillation mechanism  204  and third rotational oscillation mechanism  203  are disposed symmetric across an imaginary plane which is orthogonal to second rotational axis  102  and in which the center of reflective body  110  is located. Rotational oscillation mechanism  204  and rotational oscillation mechanism  203  each include connector bodies, vibration bodies, driving bodies, bases, and monitor elements which are disposed symmetric across the imaginary plane. 
     Specifically, fourth rotational oscillation mechanism  204  includes, as connector bodies, seventh connector body  127  and eighth connector body  128 . Seventh connector body  127  and eighth connector body  128 , and fifth connector body  125  and sixth connector body  126  which third rotational oscillation mechanism  203  includes as connector bodies are disposed symmetric across the imaginary plane. Seventh connector body  127  is disposed opposite fifth connector body  125  with respect to reflective body  110  and along second rotational axis  102 . Seventh connector body  127  has a distal end portion that is coupled to second base  162 . Seventh connector body  127  includes groove portion  150  that is provided in a position in which second rotational axis  102  is located. Groove portion  150  that is provided in seventh connector body  127  is in the shape of a slit that penetrates seventh connector body  127  in the direction (the Z-axis direction in the diagram) orthogonal to the reflective surface of reflective body  110 . In addition, groove portion  150  extends from a distal end portion of seventh connector body  127  which is connected to reflective body  110  to a proximal end portion of seventh connector body  127 . Accordingly, seventh connector body  127  can be seen as two bar-shaped members with second rotational axis  102  interposed therebetween. Fourth rotational oscillation mechanism  204  includes, as vibration bodies, seventh vibration body  147  and eighth vibration body  148 . Seventh vibration body  147  and eighth vibration body  148 , and fifth vibration body  145  and sixth vibration body  146  which third rotational oscillation mechanism  203  includes as vibration bodies are disposed symmetric across the imaginary plane. Fourth rotational oscillation mechanism  204  includes, as driving bodies, seventh driving body  157  and eighth driving body  158 . Seventh driving body  157  and eighth driving body  158 , and fifth driving body  155  and sixth driving body  156  which third rotational oscillation mechanism  203  includes as driving bodies are disposed symmetric across the imaginary plane. Like third rotational oscillation mechanism  203 , seventh driving body  157  includes seventh driving body main portion  195  and seventh piezoelectric element  196 , and eighth driving body  158  includes eighth driving body main portion  197  and eighth piezoelectric element  198 . Fourth rotational oscillation mechanism  204  includes, as a base, fourth base  164 . Fourth base  164  and third base  163  which third rotational oscillation mechanism  203  includes as a base are disposed symmetric across the imaginary plane. In this embodiment, third base  163  and fourth base  164  are integrally coupled together, and form a quadrilateral frame member as a whole. In addition, fourth rotational oscillation mechanism  204  includes seventh vibration body  147  to which seventh monitor element  177  is attached, and eighth vibration body  148  to which eighth monitor element  178  is attached. Seventh vibration body  147 , seventh monitor element  177 , eighth vibration body  148 , and eighth monitor element  178  which are included in fourth rotational oscillation mechanism  204 , and fifth vibration body  145 , fifth monitor element  175 , sixth vibration body  146 , and sixth monitor element  176  which are included in third rotational oscillation mechanism  203  are disposed symmetric across the imaginary plane. 
     In addition to the advantageous effects described in Embodiment 1 and Embodiment 2, optical reflective element  300  according to Embodiment 3 can further cause reflective body  110 , which first rotational oscillation mechanism  201  and second rotational oscillation mechanism  202  cause to rotationally oscillate about first rotational axis  101 , to rotationally oscillate about second rotational axis  102  that intersects with first rotational axis  101 . Therefore, optical reflective element  300  according to Embodiment 3 can two-dimensionally sweep an illumination position of laser light, even if there is only a beam of laser light to be reflected. 
     In this embodiment, first rotational axis  101  and second rotational axis  102  are formed such that first rotational axis  101  and second rotational axis  102  are orthogonal to each other at the approximate center of reflective body  110 . With this, the center of reflective body  110  serves as a fixed point. Accordingly, if light is incident on this fixed portion, an optical path of the light projected onto a screen is uniform, and if optical reflective element  300  is used for a projector etc., an image can be projected onto the screen with high accuracy. 
     Moreover, since a degree of the resonance sharpness (Q factor) of optical reflective element  300  that includes reflective body  110 , first rotation oscillation mechanism  201 , second rotation oscillation mechanism  202 , third rotation oscillation mechanism  203 , and fourth rotation oscillation mechanism  204  enhances, the driving frequency band of reflective body  110  narrows. Accordingly, optical reflective element  300  is less likely to be affected by a disturbance vibration. This enables reflective body  110  to stably rotationally oscillate. 
     Note that in above-described Embodiments 1 through 3, a pair of vibration bodies and a pair of driving bodies form, as a whole, a shape of a tuning fork. The pair of vibration bodies and the pair of driving bodies are disposed such that the pair of vibration bodies and the pair of driving bodies surround reflective body  110 . This disposition not only downsizes an optical reflective element, but also allows the distal end portions of the vibration bodies and the distal end portions of driving bodies to be free ends. This enables an efficient increase in the oscillation angle of reflective body  110 , thereby obtaining a large amount of vibrational energy from a small amount of energy. However, the present disclosure is not limited to the above-described Embodiments 1 through 3. For example, a vibration body and a driving body can form a bar shape. 
     For example, although first rotation oscillation mechanism  201  and second rotation oscillation mechanism  202  are disposed symmetric across an imaginary plane, and third rotation oscillation mechanism  203  and fourth rotation oscillation mechanism  204  are disposed symmetric across an imaginary plane, first rotation oscillation mechanism  201  and second rotation oscillation mechanism  202  may be disposed rotationally symmetric with respect to an axis, and third rotation oscillation mechanism  203  and fourth rotation oscillation mechanism  204  may be disposed rotationally symmetric with respect to an axis. 
     In addition, although a driving body main portion includes a piezoelectric element on one surface, the driving body main portion includes a piezoelectric element on both surfaces. Furthermore, a vibration body may include a piezoelectric element on its surface. 
     In addition, although groove portion  150  extends from a distal end portion of a connector body to a proximal end portion of the connector body, groove portion  150  may extends into a part of coupling body  149 . In addition, the length of groove portion  150  may be shorter than the length of the connector body. Furthermore, a plurality of groove portions  150  may be provided in one connector body. In that case, each groove portion  150  may have a shorter length and a dot shape. 
     It should be noted that although first driving body  183 , second driving body  184 , first vibration body  141 , and second vibration body  142  include first piezoelectric element  185 , second piezoelectric element  186 , first monitor element  171 , and second monitor element  172 , respectively, in the above-described Embodiment 1, first piezoelectric element  185 , second piezoelectric element  186 , first monitor element  171 , and second monitor element  172  need not be included as illustrated in  FIG. 9 . For example, in the case in which first driving body  183  and second driving body  184  are members that produce power by an interaction with an electrostatic force and an electromagnetic force which are externally supplied, first power generation device  211  and second power generation device  212  which generate an electrostatic force and an electromagnetic force may be provided outside an optical reflective element to vibrate first driving body  183  and second driving body  184  by either (i) changing at least one of a magnetic field and an electric field generated by the power generation devices, or (ii) changing at least one of a magnetic field and an electric field generated by first driving body  183  and second driving body  184 . In addition, first power generation device  211  and second power generation device  212  may be one integrated device. 
     Although only some exemplary embodiments of the present disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of the present disclosure. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     Since the present disclosure has an advantageous effect of downsizing an optical reflective element according to the present disclosure, the optical reflective element is useful for a small display device, a small projector, an in-vehicle head-up display device, an electrographic copying machine, a laser-beam printer, an optical scanner, an optical radar, etc.