Patent Description:
There has been known a scanning device that emits a light toward a predetermined region while deflecting the light, and detects the light returning from the predetermined region, and thus, obtains various kinds of information regarding an object positioned in the predetermined region. In such a scanning device, a movable mirror, such as a Micro Electro Mechanical System (MEMS) mirror, is disposed as a part that deflects a light. As an optical scanning device having the movable mirror, there has been proposed an optical scanning device that has an electromagnet made of a yoke and a coil wound around the yoke, generates a magnetic field by flowing an alternating current to the coil, and drives the mirror by an interaction with a magnetic field of a permanent magnet (for example, Patent Document <NUM>).

Patent Document <NUM>: <CIT>. <CIT> describes an oscillating body device, such as an optical deflector, having a structure which can be downsized without impairment of durability. <CIT> refers to a mirror scanner.

In an optical scanning device, such as the above-described prior art, a yoke has a C shape (or a U shape), and a magnetic field generating end as an end portion of the yoke is disposed to face a permanent magnet provided on an opposite side surface (that is, a backside surface) of a light reflecting surface of a mirror. In view of this, it is necessary that the backside surface of the mirror has a space corresponding to a height when the C-shaped yoke is longitudinally disposed with the magnetic field generating end upward, and thus, a dimension of the whole device is increased. Accordingly, there has been a problem that a location of the optical scanning device is limited.

The present invention has been made in consideration of the above-described points, and it is an object of the present invention to provide a mirror scanner that sufficiently drives the mirror and allows to perform optical scanning while keeping a dimension of the device down.

The invention according to claim <NUM> is a mirror scanner comprising: a mirror having a first surface that reflects a light, the mirror being swingable about a swing axis; a permanent magnet disposed on a second surface which is a surface opposite of the first surface of the mirror; a yoke having a pair of magnetic field generating ends, a pair of extending portions and a coupling portion, the pair of magnetic field generating ends being disposed at positions facing the permanent magnet in the second surface side of the mirror, the coupling portions coupling respective one ends of the pair of extending portions and the pair of magnetic field generating ends being formed on respective other ends of the pair of extending portions, the pair of extending portions and the coupling portion extending along the second surface of the mirror; and a coil wound around each of the pair of extending portions of the yoke.

The following describes a preferred example of the present invention in detail. In the description in the following example and the attached drawings, an identical reference numeral is attached to a substantially identical or equivalent part.

<FIG> is a perspective view illustrating an overall configuration of a mirror scanner <NUM> according to the example. The mirror scanner <NUM> is an optical scanning device that performs an optical deflection operation by periodically swinging a movable mirror.

The mirror scanner <NUM> has a mirror main body (hereinafter simply referred to as a main body) <NUM> that performs an optical deflection, and a yoke <NUM> and a driving circuit <NUM> as a magnetic field source. The mirror scanner <NUM> of this example is a magnetic-drive type MEMS device that operates the main body <NUM> by applying a magnetic field generated by the yoke <NUM> and the driving circuit <NUM> to the main body <NUM>.

The main body <NUM> includes a plate-shaped support plate <NUM> as a supporting portion, a pair of torsion bars <NUM> extending along a swing axis AX from the support plate <NUM>, and a mirror <NUM> swingably supported by the support plate <NUM> and the torsion bars <NUM>. Each of the torsion bars <NUM> has one end fixed to the support plate <NUM> and the other end fixed to the mirror <NUM>. The mirror <NUM> swings with respect to the support plate <NUM> with the torsion bars twisting about the swing axis.

For example, the support plate <NUM>, the torsion bars <NUM>, and the mirror <NUM> are formed of a semiconductor material. The main body <NUM> made of the support plate <NUM>, the torsion bars <NUM>, and the mirror <NUM> can be integratedly formed by processing, for example, a semiconductor wafer.

The mirror <NUM> has a light reflecting surface <NUM> as a flat plate-shaped member and having a reflectivity with respect to a predetermined light. The light reflecting surface <NUM> may, for example, be formed by depositing a metal on a surface of the plate-shaped material forming the mirror <NUM>. The light reflecting surface <NUM> of the mirror <NUM> and the opposite side surface have center portions where a permanent magnet <NUM> is disposed. In the following description, the light reflecting surface <NUM> of the mirror <NUM> is also referred to as a first surface and the opposite side surface of the light reflecting surface <NUM> is also referred to as a second surface.

In the mirror scanner <NUM> of this example, the magnetic field generated by the yoke <NUM> and the driving circuit <NUM> acts on the permanent magnet <NUM>, and the mirror <NUM> swings with a reference position as a center. For example, the mirror <NUM> swings with the position where the light reflecting surface <NUM> comes into parallel to the plate surface of the support plate <NUM> as the reference position. That is, the mirror <NUM> turns in a turning direction in a positive direction and a negative direction about the swing axis with the reference position as a <NUM>-degree position.

Corresponding to the swing of the mirror <NUM>, an angle of the light reflecting surface <NUM> viewed from the reference position (that is, a swing angle) changes. Specifically, when the magnetic field is applied to the permanent magnet <NUM> such that the torsion bars <NUM> twist about the swing axis AX, the mirror <NUM> swings about the swing axis AX while being supported by the support plate <NUM>. The light emitted from a light source (not illustrated) is reflected from the light reflecting surface <NUM> of the mirror <NUM>, and its reflection direction changes by the swing of the mirror <NUM>, and thus, the optical scanning is performed. Note that while the scanning direction one-dimensionally changes since there is one swing axis in this example, it is possible to perform two-dimensional scanning by causing the mirror <NUM> to reflect the light emitted from, for example, a plurality of light sources (for example, a multi-emitter) linearly aligned.

The yoke <NUM> is constituted of a soft magnetic material. The yoke <NUM> includes core portions 21A and 21B as a pair of core portions extending approximately parallel to one another along the same direction and a coupling portion <NUM> coupling the core portion 21A to the core portion 21B. That is, the yoke <NUM> has a C shape (a U shape) in this example.

A first coil portion 23A is formed of a steel wire wound around the core portion 21A of the yoke <NUM>. A second coil portion 23B is formed of a steel wire wound around the core portion 21B. Note that the first coil portion 23A and the second coil portion 23B are configured by using one common steel wire in this example. That is, it is configured such that the current flows simultaneously to the first coil portion 23A and the second coil portion 23B. Note that the first coil portion 23A and the second coil portion 23B may be configured using respective separate steel wires, and the current that flows to each of them may be individually controllable.

The yoke <NUM> has magnetic field generating ends 24A and 24B as a pair of magnetic field generating end portions. The magnetic field generating end 24A is provided in the proximity of an end portion opposite of the connecting portion with the coupling portion <NUM> of the core portion 21A, and has a projecting shape projecting in a direction perpendicular to the extension direction of the core portion 21A. Similarly, the magnetic field generating end 24B is provided in the proximity of the end portion opposite of the connecting portion with the coupling portion <NUM> of the core portion 21B, and has a projecting shape projecting in a direction perpendicular to the extension direction of the core portion 21B.

In other words, the magnetic field generating ends 24A and 24B have a shape projecting in a direction perpendicular from a planar surface (that is, one planar surface constituted of surfaces of the core portion 21A, the core portion 21B, and the coupling portion <NUM>) including each of the straight lines along the extension direction of the core portions 21A and 21B. For example, the magnetic field generating ends 24A and 24B are formed by adding, for example, a metallic material processed into a triangular prism shape in the proximity of each of the end portions of the core portion 21A and the core portion 21B as illustrated in <FIG>.

The driving circuit <NUM> is a circuit that applies a drive current to the first coil portion 23A and the second coil portion 23B. For example, the driving circuit <NUM> applies the alternating current for driving the mirror <NUM> to resonate to the first coil portion 23A and the second coil portion 23B as the drive current. This causes the yoke <NUM> to function as an electromagnet to generate an alternate current magnetic field from the magnetic field generating end 24A and the magnetic field generating end 24B.

In the mirror scanner <NUM> of this example, the core portions 21A and 21B of the yoke <NUM> are disposed to extend along the plate surface of the support plate <NUM> and the second surface of the mirror <NUM> at the reference position in the second surface (that is, a surface opposite of the light reflecting surface <NUM>) side of the mirror <NUM>. For example, the yoke <NUM> is disposed such that the extension direction of the core portions 21A and 21B comes approximately parallel to the plate surface of the support plate <NUM> and the second surface of the mirror <NUM> at the reference position. The yoke <NUM> is disposed such that the magnetic field generating ends 24A and 24B are at positions facing the permanent magnet <NUM> in the second surface side of the mirror <NUM>.

<FIG> is a drawing illustrating a positional relation between the main body <NUM> and the yoke <NUM>. Note that the driving circuit <NUM> is not illustrated here.

Note that the yoke <NUM> is fixed to a base <NUM> by a jig <NUM> as illustrated in <FIG>, and is disposed at the position illustrated in <FIG>. The jig <NUM> fixes the yoke <NUM> on the base <NUM> by sandwiching the coupling portion <NUM> of the yoke <NUM> in a direction perpendicular to the extension direction of the core portions 21A and 21B (that is, the direction perpendicular to the plate surface of the support plate <NUM>). The jig <NUM> is, for example, constituted of a material high in thermal conductivity, such as aluminum, and of non-magnetic body. Besides the function of fixing the yoke <NUM>, the jig <NUM> also has a function of dissipating heat generated in the yoke <NUM> by the driving of the mirror scanner <NUM> by the heat conduction.

As illustrated in <FIG>, the mirror scanner <NUM> of this example, the yoke <NUM> is disposed such that the yoke <NUM> extends (that is, the core portions 21A and 21B extend along the second surface of the mirror <NUM> at the reference position) along a main surface of the main body <NUM> (that is, the plate surface of the support plate <NUM> and the second surface of the mirror <NUM> at the reference position). In view of this, the mirror scanner <NUM> has a width smaller in a direction perpendicular to the main surface of the main body <NUM>. In other words, the mirror scanner <NUM> of this example has a small length in a height direction with a placement surface of the mirror <NUM> as a reference.

<FIG> is a drawing illustrating a configuration of the mirror scanner <NUM> of a comparative example having a different shape and an arrangement of a yoke from those of the mirror scanner <NUM> of the example. The mirror scanner <NUM> of the comparative example is constituted of the main body <NUM>, a yoke <NUM>, and the driving circuit <NUM>.

The yoke <NUM> has a C shape made of a core portion <NUM> and extending portions 42A and 42B extending parallel to one another from both ends of the core portion <NUM>. A coil <NUM> is wound around the core portion <NUM>.

The yoke <NUM> has magnetic field generating ends 44A and 44B extending continuously from end portions opposite of a connecting portion with the core portion <NUM> of the extending portions 42A and 42B. The magnetic field generating ends 44A and 44B are unlike the magnetic field generating ends 24A and 24B of the mirror scanner <NUM> of this example (see <FIG>), and do not project in a direction perpendicular to a planar surface including the respective straight lines along the extension directions of the extending portions 42A and 42B, and project in a direction forming a leading end of a C shape on this planar surface.

The yoke <NUM> is disposed such that the magnetic field generating ends 44A and 44B face the permanent magnet <NUM> in the second surface side of the mirror <NUM>. Therefore, for example, when the mirror scanner <NUM> of the comparative example is horizontally placed, the yoke <NUM> is disposed such that the extension directions of the extending portions 42A and 42B are perpendicular directions (that is, a height direction) with the core portion <NUM> as a bottom surface.

<FIG> is a drawing illustrating a positional relation between the main body <NUM> and the yoke <NUM> in the mirror scanner <NUM> of the comparative example. Note that the driving circuit <NUM> is not illustrated here.

In the mirror scanner <NUM> of the comparative example, the yoke <NUM> is disposed such that the plate surface of the support plate <NUM> and the second surface of the mirror <NUM> at the reference position are perpendicular to the extending portions 42A and 42B. The magnetic field generating ends 44A and 44B are continuously extending from the respective end portions of the extending portions 42A and 42B. In view of this, the mirror scanner <NUM> has a large width in a direction perpendicular to the plate surface of the support plate <NUM> (that is, the height obtained by combining the main body <NUM> and the yoke <NUM> when the surface opposite of the surface facing the main body <NUM> of the yoke <NUM> is the bottom surface).

In contrast to this, in the mirror scanner <NUM> of this example, the magnetic field generating ends 24A and 24B have a shape projecting from the planar surface including the respective straight lines along the extension directions of the core portions 21A and 21B. In view of this, as illustrated in <FIG>, the yoke <NUM> can be disposed such that the yoke <NUM> extends along the main surface of the main body <NUM> (for example, the extension directions of the core portions 21A and 21B come approximately parallel to the main surface of the main body <NUM>).

Accordingly, in the mirror scanner <NUM> of this example, compared with the mirror scanner <NUM> of the comparative example, the width (that is, the length in the height direction with the placement surface of the yoke <NUM> as the reference) of the mirror scanner <NUM> in the direction perpendicular to the main surface of the main body <NUM> can be shortened. This ensures keeping the device dimension as the whole mirror scanner <NUM> small.

In the mirror scanner <NUM> of the comparative example, the coil <NUM> is positioned immediately below the permanent magnet <NUM>. In view of this, in order not to cause the coil <NUM> to directly affect the operation of the permanent magnet <NUM>, it is necessary to keep a distance between the permanent magnet <NUM> and the coil <NUM> by making the magnetic field generating ends 44A and 44B have a certain height or more. In contrast to this, in the mirror scanner <NUM> of this example, since the first coil portion 23A and the second coil portion 23B are disposed at a position displaced from immediately below the permanent magnet <NUM>, the heights of the magnetic field generating ends 24A and 24B can be kept low.

In the mirror scanner <NUM> in this example, the coils are wound around the core portions 21A and 21B as the pair of core portions. The core portions 21A and 21B are disposed so as to extend (for example, to be approximately parallel) along the plate surface of the support plate <NUM> and the second surface of the mirror <NUM> at the reference position. In such a configuration, since the lengths of the core portion 21A and the core portion 21B do not affect the height of the mirror scanner <NUM>, it is possible to increase the number of turns of the coils by extending the lengths of the core portions 21A, 21B as the portions around which the coils are wound without increasing the height of the mirror scanner <NUM>.

The mirror scanner <NUM> in this example ensures increasing the number of turns of the coil wound around the core portion although the height is lower than that of the mirror scanner <NUM> in the comparative example. For example, when the widths of the mirror scanner <NUM> and the mirror scanner <NUM> are the same, that is, when the core portion <NUM> has a length the same as each of the lengths of the core portions 21A, 21B, the coil wire that can be wound around the core portion is approximately double. That is, it is possible to increase the number of turns of the coil while reducing the height and without changing the size in the width direction (that is, the length in the extension directions of the core portions 21A and 21B), and thus ensuring swinging the mirror <NUM> with a smaller drive current.

<FIG> is a graph illustrating a relation between a drive current applied by the driving circuit <NUM> and an oscillation angle (that is, the maximum value of a swing angle with the reference position as the center) in the swing of the mirror <NUM>. The horizontal axis indicates an effective value of the current value (mA) of the drive current, and the vertical axis indicates the oscillation angle of the mirror. Here, the mirror scanner <NUM> of this example is indicated by the solid line, and the mirror scanner <NUM> of the comparative example is indicated by the dashed line.

The mirror scanner <NUM> of this example ensures obtaining the same oscillation angle with the drive current of the current value of half or less of that of the mirror scanner <NUM> of the comparative example. For example, while the mirror scanner <NUM> of the comparative example needs the drive current of <NUM> mA or more of effective value to obtain the oscillation angle of <NUM>°, the mirror scanner <NUM> of this example obtains the oscillation angle of <NUM>° with the drive current of less than <NUM> mA of effective value.

Thus, the mirror scanner <NUM> of this example can obtain the equal force with a small electric power compared with that of the comparative example. Accordingly, with the mirror scanner <NUM> of this example, it is possible to perform the optical scanning equal to the conventional ones while reducing the power consumption.

Note that when the number of turns of coil is desired to be increased in the mirror scanner <NUM> of the comparative example, it is considered to wind coils around the extending portions 42A and 42B illustrated in <FIG>. However, the extending portions 42A and 42B extend in the direction perpendicular to the plate surface of the support plate <NUM> and the second surface of the mirror <NUM>, and thus, a length corresponding to the number of turns of the coil is necessary, thereby resulting in an increased length (that is, the height of the mirror scanner <NUM>) in the direction perpendicular to the plate surface of the support plate <NUM>. Accordingly, the mirror scanner <NUM> of the comparative example cannot increase the number of turns of the coil while keeping the height of the mirror scanner <NUM> low.

As described above, the mirror scanner <NUM> of this example ensures keeping the height of the whole device low. Also, it is possible to increase the number of turns of the coil without increasing the height of the device. Accordingly, use of the mirror scanner <NUM> of this example ensures performing the optical scanning by sufficiently driving the mirror while reducing the device dimension and the electric power consumption.

When the temperature of the yoke increases, the resistance value of the conducting wire of the coil increases, which increases the power consumption. In view of this, the heat dissipation of the yoke is effective for reducing the power consumption. In the mirror scanner <NUM> of this example, the yoke <NUM> is fixed on the base <NUM> by the jig <NUM> as illustrated in <FIG>. The jig <NUM> is constituted of the material high in thermal conductivity, such as aluminum, and fixes the whole coupling portion <NUM> so as to sandwich the whole coupling portion <NUM>, and therefore, has a large area of a contact surface with the yoke <NUM>. Accordingly, the heat of the yoke <NUM> can be efficiently dissipated.

Since it is possible to keep the height of the mirror scanner <NUM> low as described above, there is little limitation of location. Accordingly, for example, when it is used as an optical scanning device for mounting in a vehicle, it is possible to dispose the mirror scanner <NUM> in a space on a bumper, a dashboard, or the like of the vehicle.

Note that the present invention is not limited to the above-described embodiment. For example, the above-described embodiment has described the example in which the mirror <NUM> is swung about one swing axis AX. However, unlike this, the mirror <NUM> may be configured to be swung about two swing axes. For example, it is possible to swing the mirror <NUM> about the two swing axes by configuring the mirror swingable about the two mutually orthogonal swing axes, and disposing two yokes having a configuration similar to that of the yoke <NUM> of the above-described example such that respective pairs of core portions extend along a plate surface of a support plate while magnetic field generating ends face a permanent magnet.

The above-described example has described the case where the core portions 21A and 21B as the pair of core portions extend approximately parallel to one another along the same direction. However, the configuration is not limited to this, and the core portions 21A and 21B may have respective extension directions configured to form an angle of less than <NUM> degrees to one another. Also, the core portions 21A and 21B may have lengths different from one another.

Claim 1:
A mirror scanner (<NUM>, <NUM>) comprising:
a mirror (<NUM>) having a first surface that reflects a light, the mirror being swingable about a swing axis;
a permanent magnet (<NUM>) disposed on a second surface which is a surface opposite of the first surface of the mirror ,
a yoke (<NUM>, <NUM>) having a pair of magnetic field generating ends, a pair of extending portions (42a, 42b) and a coupling portion (<NUM>, <NUM>), the pair of magnetic field generating ends being disposed at positions facing the permanent magnet in the second surface side of the mirror, the coupling portion coupling respective one ends of the pair of extending portions and the pair of magnetic field generating ends being formed on respective other ends of the pair of extending portions; and
a coil wound around each of the pair of extending portions of the yoke,
wherein the pair of extending portions and the coupling portion extend along the second surface of the mirror.