Patent Description:
There has been known a MEMS (Micro Electro Mechanical Systems) light deflector and an optical scanning device provided therewith (e.g., Patent Literatures <NUM> and <NUM>). The MEMS light deflector includes a mirror unit, which performs reciprocating rotation about a rotation axis, reflects light from a light source in a direction based on the deflection angle of the mirror unit, and emits the reflected light as scanning light.

The scanning position of scanning light in an irradiation region changes according to the deflection angle of the mirror unit. Therefore, it is necessary to detect the deflection angle of the mirror unit in order to properly control the irradiation quality of the scanning light.

The optical scanning device of Patent Literature <NUM> includes a PD (photodiode) disposed in the emission direction of reflected light when the mirror unit reaches an end of a deflection angle range. Thus, when the mirror unit reaches a predetermined deflection angle at the end of the deflection angle range, the reflected light is detected by the PD.

In the optical scanning device of Patent Literature <NUM>, the reflection surface of a mirror unit is formed of a diffraction grating. In the optical scanning device, the zero-order diffracted light emitted from the mirror unit is used for the intended scanning light. On the other hand, the first-order diffracted light enters a light receiving element and is used for detecting a deflection angle.

Attention is drawn to the document <CIT>. The document sets out to enable a reduction in the number of parts of drive mechanisms of a plurality of movable members by mounting mirrors, which reflect light, respectively to holders and other movable members, which are capable of rotating around a prescribed axis, by means of springs, and, in addition, attaching coils respectively to the movable member sides as drive mechanisms for magnetically driving the respective movable members, and attaching rod-shaped magnets, the magnetic field of which acts in common with respective coils, in the members of one stator side.

Further attention is drawn to document <CIT>. Here, linear spot velocity or position variations are measured in a scanning system by a process and apparatus. The process comprises providing at least two radiation detectors that can move in tandem across a scan line, the two radiation detectors being spaced apart by a distance d; positioning the at least two radiation detectors at a first point on the scan line; scanning the at least two radiation detectors with scanning radiation and recording the position of the two detectors along the scan line and the time taken for the scanning radiation to scan from a first of the at least two radiation detectors to a second of the at least two radiation detectors while the at least two radiation detectors are positioned at the first point; moving the at least two radiation detectors to a second point on the scan line maintaining the distance d between the at least two radiation detectors; and again scanning the at least two radiation detectors with scanning radiation and recording the position of the two detectors along the scan line and the time taken for the scanning radiation to scan from a first of the at least two radiation detectors to a second of the at least two radiation detectors while the at least two radiation detectors are positioned at the second point.

Also, attention is drawn to document <CIT>. It describes that a light is emitted from a light emitting element toward the other surface in a thickness direction of a scanning mirror which can be angularly displaced about an axial line. At least either one of a first light receiving portion and a second light receiving portion receives a light which is emitted from the light emitting element and reflected by a reflecting mirror. The first light receiving portion, the second light receiving portion, and the signal output section produce an electronic signal containing position information which indicates a position which is irradiated with the above-mentioned light. This position information indicates an amount of angular displacement of the scanning mirror. On the basis of this position information, a driving section scans the scanning mirror so that the predetermined irradiation position can be irradiated with a light emitted from a first light source. Finally, attention is drawn to a document <CIT>. Here a laser scanner includes a light source, a scanning mirror, and a first photodetector. The scanning mirror includes: a first reflective surface reflects the laser light from the light source; and a second reflective surface that reflects, toward the photodetector , the laser light reflected from the target object. The first reflective surface and at least part of the second reflective surface are disposed at mutually different angles. When a first optical axis passing through the target object and the first reflective surface is parallel with a second optical axis passing through the target object and the second reflective surface, a third optical axis passing through the first reflective surface and the light source and a fourth optical axis passing through the second reflective surface and the photodetector are at a predetermined angle relative to one another.

In the optical scanning devices of Patent Literatures <NUM> and <NUM>, errors occur in the detection of the deflection angle of the mirror unit due to variations in the mounting position and characteristics of the PD that detects reflected light and diffracted light.

An object of the present invention is to provide an optical scanning device capable of compensating for the variations in the mounting position and the characteristics of a light detection unit when detecting the deflection angle of a mirror unit.

In accordance with the present invention an optical scanning device in, as set forth in the independent claim is provided.

According to the present invention, the first and the second light detectors are disposed on the scanning trajectory of a scanning light spot, and receive each portion of an index light spot divided by the division line. Further, the deflection angle of the mirror unit is detected based on the output of the first light detector and the output of the second light detector. The variations in the mounting position and characteristics of the light detection unit are reflected on the relationship between the output of the first light detector and the output of the second light detector, thus making it possible to compensate for the variations when detecting the deflection angle of the mirror unit.

Preferably, in the optical scanning device in accordance with the present invention,
the deflection angle detection unit performs the comparison between an output of the first light detector and an output of the second light detector based on a difference between the two outputs.

According to the configuration, a first deflection angle is detected based on the difference between the output of the first and the output of the second light detector. This makes it possible to improve the accuracy of detecting the deflection angle of the mirror unit.

Preferably, in the optical scanning device in accordance with the present invention,
the deflection angle detection unit performs comparison of an output of the first light detector and an output of the second light detector based on a ratio of the two outputs.

According to the configuration, a first deflection angle is detected based on the ratio between the output of the first light detector and the output of the second light detector. This makes it possible to improve the accuracy of detecting the deflection angle of the mirror unit.

Preferably, in the optical scanning device in accordance with the present invention,
the deflection angle detection unit uses a deflection angle of the mirror unit associated with a traveling direction of the index light as an index deflection angle, and detects that a deflection angle of the mirror unit about the first rotation axis has reached the index deflection angle based on an output of the first light detector and an output of the second light detector.

According to the configuration, it is detected that the deflection angle of the mirror unit has reached an index deflection angle based on the output of the first light detector and the output of the second light detector. This makes it possible to improve the accuracy of detecting the deflection angle of the mirror unit.

Preferably, in the optical scanning device in accordance with the present invention,
the deflection angle detection unit generates an intermediate value based on comparison of an output of the first light detector and an output of the second light detector, uses an intermediate value obtained in the case where the scanning light spot is not received as a reference value, and detects the first deflection angle based on a calibrated value obtained by calibrating the intermediate value by the reference value.

According to the configuration, an intermediate value obtained when a scanning light spot is not received is used as a reference value, and a deflection angle is detected based on a calibrated value obtained by calibrating the intermediate value by the reference value. This makes it possible to prevent variations in detected deflection angles from one optical scanning device to another.

Preferably, in the optical scanning device in accordance with the present invention,
the deflection angle detection unit uses, as an index deflection angle, a deflection angle of the mirror unit associated with a traveling direction of the index light, and detects a timing at which a deflection angle of the mirror unit becomes the index deflection angle based on a timing at which a sign of the difference is reversed.

According to the configuration, the timing at which the mirror unit has reached an index deflection angle is detected based on the timing at which the sign of a difference is reversed. This makes it possible to detect a versatile timing.

Preferably, in the optical scanning device in accordance with the present invention,
the intermediate value is a normalized difference Ev defined by Formula <NUM>, which will be discussed later.

According to the configuration, the first deflection angle is detected using the normalized difference Ev, thus making it possible to use a versatile optical scanning device regardless of the type of optical scanning device.

Preferably, in the optical scanning device in accordance with the present invention,.

The interval between the two light detection units is fixed. This configuration makes it possible to smoothly detect the angle range of a deflection angle by detecting the time difference.

Preferably, in the optical scanning device in accordance with the present invention,
the pair of inclined surfaces are formed symmetrically with respect to a vertical plane perpendicular to a flat reflection surface of the flat reflection part.

According to the configuration, a light receiving intensity of an index light spot in a light detection unit can be increased.

Preferably, in the optical scanning device in accordance with the present invention,
in the case where a tilt angle of the inclined surfaces of the longitudinal groove with respect to the flat reflection surface is denoted by α, <NUM> • α is within a range of <NUM>° to <NUM>°.

According to the configuration, the light receiving intensity of an index light spot in the light detection unit can be increased.

According to the configuration, the inclined surfaces of the groove-shaped reflection part can be smoothly formed to have desired tilt angles by using the Miller index of the silicon crystal surface.

Preferably, in the optical scanning device in accordance with the present invention,
the longitudinal groove is open at least partly on the back surface side.

According to the configuration, the accuracy of detecting the deflection angle of the mirror unit can be enhanced by preventing thrice reflected light from entering the light detection unit.

According to the configuration, the length of the inclined surface for preventing thrice reflected light from entering the light detection unit can be appropriately determined.

Preferably, in the optical scanning device in accordance with the present invention,
the groove-shaped reflection part is disposed in such a manner as to overlap the first rotation axis in a front view of the mirror unit.

According to the configuration, a deflection angle can be detected without hindrance when the mirror unit swings to either side with respect to the front view of the light deflector.

Preferably, in the optical scanning device in accordance with the present invention,
the groove-shaped reflection part occupies a central part of the mirror unit.

According to the configuration, the intensity of an index light spot can be increased as the intensity of light incident on the groove-shaped reflection part increases.

According to the configuration, the light detection unit is formed in a long narrow shape in a scanning direction of the index light spot at the time of reciprocating rotation of the mirror unit about the second rotation axis. This enables a light deflector, which two-dimensionally scans a scanning light spot, to detect a first deflection angle without hindrance.

Preferably, in the optical scanning device in accordance with the present invention,
the groove-shaped reflection part has a plurality of the longitudinal grooves.

According to the configuration, the light receiving intensity of an index light spot in a light detection unit can be increased by providing a plurality of longitudinal grooves.

Preferably, in the optical scanning device in accordance with the present invention,
a pitch Dp of the plurality of longitudinal grooves is set according to Formula <NUM>, which will be described later.

According to the configuration, a light detection unit is at a position where enhancement takes place by the mutual interference of index light spots from the longitudinal grooves. This makes it possible to increase the intensity of an index light spot received by the light detection unit.

A plurality of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In the illustrated embodiments, the same reference numerals are used for the same components. In each embodiment, the reference numerals of a pair of components have the same numbers with different subscript letters. When elements of reference numerals with letters are collectively referred to, reference numerals of only numbers without letters are used.

<FIG> is a configuration diagram of a single-axis (one-dimensional) scanning type optical scanning device <NUM>. As a single-axis scanning type optical scanning device, the optical scanning device <NUM> includes a single-axis scanning type light deflector <NUM>. The optical scanning device <NUM> includes a control unit <NUM>, light detection units 4a and 4b, and a light source <NUM> in addition to the light deflector <NUM>.

The light source <NUM> is, for example, a laser light source. The light source <NUM> emits original light La as original light. The original light La enters the front surface of a mirror unit <NUM> as the incident light of the light deflector <NUM>. In this example, the front surface of the circular mirror unit <NUM> is composed of a flat reflection part <NUM>, which constitutes the majority thereof, and a groove-shaped reflection part <NUM> disposed at a center O of the mirror unit <NUM>.

The reflection surface of the flat reflection part <NUM> is formed of a flat plane as a flat reflection surface. On the other hand, the groove-shaped reflection part <NUM> has a V-groove-shaped reflection surface.

Of the original light La, the light incident on the flat reflection part <NUM> turns into scanning light Lb, which is then emitted from the flat reflection part <NUM>. Of the original light La, the light incident on the groove-shaped reflection part <NUM> turns into detection light Lc, which is then emitted from the groove-shaped reflection part <NUM>. The detection light Lc includes once reflected light L1, twice reflected light L2, and thrice reflected light L3. The once reflected light L1, the twice reflected light L2, and the thrice reflected light L3 will be described in detail with reference to <FIG>.

The control unit <NUM> includes a controller <NUM>, a light source driver <NUM>, and an actuator driver <NUM>. The controller <NUM> further includes a deflection angle detection unit <NUM>.

The light source driver <NUM> and the actuator driver <NUM> drive the light source <NUM> and a piezoelectric actuator <NUM> of the light deflector <NUM>, respectively. The light source <NUM> is driven by the light source driver <NUM> and controlled to be turned on and off, and the luminous intensity thereof is also controlled at the time of lighting. The piezoelectric actuator <NUM> of the light deflector <NUM> controls the reciprocating rotation of the mirror unit <NUM> about a rotation axis <NUM> by being driven by the actuator driver <NUM>.

The deflection angle detection unit <NUM> detects a deflection angle θ (<FIG>) of the mirror unit <NUM> of the light deflector <NUM> based on a detection signal from each light detection unit <NUM>. The controller <NUM> drives the light source <NUM> and the piezoelectric actuator <NUM> while synchronizing these two with each other based on the deflection angle θ.

The single-axis scanning type light deflector <NUM> is the same as a known single-axis piezoelectric type light deflector (e.g., <CIT>) except for the mirror unit <NUM>. Therefore, the light deflector <NUM> will be briefly described. For convenience of explaining the configuration of the light deflector <NUM>, a three-axis Cartesian coordinate system of X-axis, Y-axis, and Z-axis will be defined.

The rotation axis <NUM> passes through the center O of the mirror unit <NUM> and extends in a Y-axis direction. Torsion bars 31a and 31b extend from the sides of the mirror unit <NUM> along the rotation axis <NUM>. Piezoelectric actuators 32a to 32d all extend in an X-axis direction. The piezoelectric actuators 32a and 32b are provided on both sides of the torsion bar 31a in the X-axis direction, and interposed between the torsion bar 31a and a support frame <NUM>. The piezoelectric actuators 32c and 32d are provided on both sides of the torsion bar 31b in the X-axis direction, and interposed between the torsion bar 31b and the support frame <NUM>.

The dimensions of the sections of the mirror unit <NUM> are, for example, as follows. The mirror unit <NUM> has a circular shape of <NUM> mmφ to <NUM> mmφ. The groove-shaped reflection part <NUM> has a square shape, one side of which measures several <NUM> to several <NUM>.

The piezoelectric actuator <NUM> rotates the part thereof coupled with the torsion bar <NUM> about the rotation axis <NUM> in a reciprocating manner. This causes the torsional vibration of the torsion bar <NUM> to be transmitted to the mirror unit <NUM>, and the mirror unit <NUM> rotates about the rotation axis <NUM> at a predetermined resonant frequency. As a result, the scanning light Lb is displaced in a reciprocating manner with a deflection width (deflection angle range) Wb.

The scanning light Lb and the twice reflected light L2 (the detection light Lc) illustrated in <FIG> will be described in detail with reference to the next <FIG>. A scanning light spot <NUM> is a light spot generated at an irradiation destination by the scanning light Lb generated by the original light La reflected on the flat reflection part <NUM>. Index light spots 51a and 51b are light spots generated at an irradiation destination by the twice reflected light L2 of the detection light Lc generated by the original light La reflected on the groove-shaped reflection part <NUM>. The scanning light spot <NUM> and the index light spots 51a and 51b will be described in detail with reference to <FIG> and after.

<FIG> is a cross-sectional view illustrating the groove-shaped reflection part <NUM> cut by a plane which passes through the center O of the mirror unit <NUM> and which is perpendicular to the rotation axis <NUM>. The deflection angle θ of the mirror unit <NUM> illustrated in <FIG> is <NUM>°. In this embodiment, the deflection angle θ is defined as <NUM>° when a normal <NUM> of the flat reflection part <NUM> is parallel to the Z-axis. In <FIG>, the negative side of the Z-axis is the front surface side of the mirror unit <NUM>, and the positive side of the Z-axis is the back surface side of the mirror unit <NUM>.

The reflected light emitted from the mirror unit <NUM> comes in the scanning light Lb and the detection light Lc. The detection light Lc includes the once reflected light L1, the twice reflected light L2, and the thrice reflected light L3.

The groove-shaped reflection part <NUM> has one longitudinal groove <NUM> that extends in parallel to the Y-axis. The longitudinal groove <NUM> is illustrated in the cross-sectional view of <FIG>. The longitudinal groove <NUM> is formed of a V-groove having a pair of inclined surfaces 42a and 42b facing each other such that the groove width decreases toward the bottom.

<FIG> is an explanatory diagram illustrating the relationship between the deflection angle θ of the mirror unit <NUM> and the emission direction of each detection light Lc. In <FIG>, it is assumed that the original light La is incident on the center O of the mirror unit <NUM> from the direction of the deflection angle θ = -<NUM>°. The normal <NUM> extends vertically with respect to the flat reflection surface of the flat reflection part <NUM>.

An emission angle γ will be defined with respect to the emission directions of the scanning light Lb and the detection light Lc from the mirror unit <NUM>. The emission angle γ is defined as the emission direction of reflected light with respect to the positive direction of the Z-axis. In <FIG>, the original light La travels in parallel to the Z-axis and toward the negative side from the positive side of the Z-axis, so that the emission angle γ becomes an angle in the direction of emission from the mirror unit <NUM> with respect to the original light La having a reversed direction. Regarding the sign of the emission angle γ, the positive side and the negative side of the X-axis are defined as positive and negative, respectively.

The emission angles γ of the once reflected light L1 and the thrice reflected light L3 change according to the deflection angle θ. On the other hand, the emission angle γ of the twice reflected light L2 is fixed independently of the deflection angle θ. In <FIG>, the emission angle γ of the twice reflected light L2 is ±<NUM>°.

<FIG> is an explanatory diagram of the twice reflected light L2. Symbols α1 and α2 denote the tilt angles of the inclined surfaces 42a and 42b with respect to the flat reflection surface of the flat reflection part <NUM>. The tilt angle α refers to the tilt angles of the inclined surfaces 42a and 42b with respect to a plane parallel to the flat reflection part <NUM>. In the illustrated embodiment, α1 = α2 = <NUM>°. The original light La is incident on the groove-shaped reflection part <NUM> from a predetermined direction.

A symbol γ' denotes the intersection angle between the original light La and the twice reflected light L2. An incident angle A of the original light La with respect to the inclined surface 42a changes according to the deflection angle θ. The sum of the interior angles of a triangle is <NUM>°, so that γ' + <NUM> • A + <NUM> • (<NUM>° - A - α1 - α2) = <NUM>° holds. As a result, y' takes the fixed value of γ' = <NUM> • α1 + <NUM> · α2 - <NUM>° regardless of the deflection angle θ of the mirror unit <NUM>. Therefore, if the incident direction of the original light La is set to the direction parallel to the Z-axis, then γ' = γ applies, and the emission angle γ of the twice reflected light L2 takes a fixed value regardless of the deflection angle θ. If α1 = α2 = <NUM>°, then the emission angle γ of the twice reflected light L2 takes the fixed value of ±<NUM>°.

As will be described later with reference to <FIG> and after, the twice reflected light L2 becomes the index light for detecting the deflection angle θ of the mirror unit <NUM>. Therefore, the emission angle γ of the twice reflected light L2 is referred to especially as "the index angle.

The reason for setting the emission direction of the twice reflected light L2 to <NUM>° is as follows. The reason is connected to the crystal orientation of the silicon of a wafer for manufacturing the light deflector <NUM> and a light deflector <NUM>, which will be described later. More specifically, α1 = α2 = α = <NUM>° can be easily obtained by using the crystal orientation of silicon.

More specifically, when manufacturing the light deflector <NUM> from a silicon substrate, the Miller index of a main surface is (<NUM>) in a typical silicon substrate. On the other hand, the silicon crystal has crystal planes at (<NUM>) and (<NUM>), and the intersection angle between (<NUM>) and (<NUM>) is <NUM> °. Therefore, if the front surface of a silicon substrate is processed by anisotropic etching, then the longitudinal groove <NUM> having the inclined surface <NUM> of the tilt angle α = <NUM>° can be easily manufactured.

In detail, the (<NUM>) planes of the inclined surfaces 42a and 42b can be selectively formed by using an alkaline aqueous solution such as KOH (potassium hydroxide), TMAH (tetramethylammonium hydroxide), or EDP (ethylene diaminepyrocatechol) as an etchant in the case of anisotropic etching. In the case where a silicon substrate having a main surface of (<NUM>) is used, a stable α of <NUM>° can be obtained as an intersection angle between the (<NUM>) plane and the (<NUM>) plane.

<FIG> is a graph illustrating the relationship between the deflection angle θ of the mirror unit <NUM> and the emission angle γ of each of the reflected lights L1 to L3 from the light deflector <NUM>. In <FIG>, α1 = α2 = <NUM>° applies.

From <FIG>, the emission angles γ of the once reflected light L1 and the thrice reflected light L3 change according to the deflection angle θ. On the other hand, it can be seen that the emission angle γ of the twice reflected light L2 is fixed to approximately <NUM>° in absolute value for both the twice reflected light L2 on the negative side and the twice reflected light L2 on the positive side.

<FIG> are graphs illustrating the relationship at various deflection angles θ between the intensities of the index light spots 51a and 51b in the light detection unit 4a, which is one light detection unit, and the light detection unit 4b, which is the other light detection unit, respectively, and the tilt angle difference between the inclined surfaces 42a and 42b (= α1 - α2). The intensity scale of the index light (twice reflected light L2) on the vertical axis shows relative values.

From <FIG>, it can be seen that the relative intensity of the twice reflected light L2 over the entire deflection width of the mirror unit <NUM> can be increased when the tilt angle difference is <NUM>°.

<FIG> are graphs illustrating the relationship at various deflection angles θ between the tilt angle sum of the tilt angle α1 of the inclined surface 42a and the tilt angle α2 of the inclined surface 42b (= α1 + α2) and the intensity of index light in the light detection unit 4a (the one light detection unit <NUM>) and the light detection unit 4b (the other light detection unit <NUM>), respectively. In the graphs of <FIG>, α1 = α2 = α, and the sum of tilt angles = <NUM> · α.

From <FIG>, it can be seen that, when the mirror unit <NUM> is swung with symmetry with respect to a mirror vertical surface <NUM>, setting the range of the sum of tilt angles to <NUM>° to <NUM>°, especially to approximately <NUM>° to approximately <NUM>°, is advantageous to increase the relative intensity of the twice reflected light L2. "<NUM> · <NUM>°" is included in the range of <NUM>° to <NUM>° as the advantageous sum of tilt angle.

<FIG> is a schematic explanatory diagram of drawing by the optical scanning device <NUM>. The optical scanning device <NUM> is a one-dimensional drawing type optical scanning device, so that a drawing area <NUM> is a one-dimensional drawing area accordingly. In the case of a two-dimensional drawing type optical scanning device (the light deflector <NUM> in <FIG> and <FIG>, which will be described later), the drawing area <NUM> will be a two-dimensional area that expands not only horizontally but also vertically.

The mirror unit <NUM> performs reciprocating rotation about the rotation axis <NUM>. Of the original light La incident on the mirror unit <NUM>, a part that is incident on the flat reflection part <NUM> turns into the scanning light Lb, which is emitted from the mirror unit <NUM>. The scanning light Lb generates the scanning light spot <NUM> at an irradiation destination. The scanning light spot <NUM> reciprocates along a scanning trajectory <NUM> as the mirror unit <NUM> performs the reciprocating rotation about the rotation axis <NUM>. The drawing area <NUM> is set in the central area of the scanning trajectory excluding both end portions from the whole of the scanning trajectory <NUM>.

Of the original light La incident on the mirror unit <NUM>, a part that is incident on the groove-shaped reflection part <NUM> turns into the detection light Lc, which is emitted from the mirror unit <NUM>. The emission angle γ of the twice reflected light L2 of the detection light Lc is ±<NUM>° independently of the reciprocating rotation of the mirror unit <NUM> about the rotation axis <NUM>.

Light detectors 54a and 54b are composed of, for example, PDs (photodetectors). The light detectors 54a and 54b are disposed in the directions of -<NUM>° and +<NUM>°, respectively, as a first light detector and a second light detector to receive index light spots 51a and 51b of the twice reflected light L2. The positions of the light detectors 54a and 54b are set outside the drawing area <NUM> in the scanning trajectory <NUM>.

<FIG> is a schematic diagram illustrating the relationship between the scanning light spot <NUM> and index light spots 51a and 51b, and the light detection units 4a and 4b. The scanning light spot <NUM> is generated at the irradiation destination of the scanning light Lb generated when the original light La is reflected on the flat reflection part <NUM>. The index light spots 51a and 51b are generated on the light receiving surfaces of the light detection units 4a and 4b, which are the irradiation destinations of twice reflected light L2a and twice reflected light L2b which are generated when the original light La is reflected on the groove-shaped reflection part <NUM>.

The light detection units 4a and 4b are positioned on the scanning trajectory <NUM> of the scanning light spot <NUM>, and also positioned on the light paths of the twice reflected light L2a and the twice reflected light L2b.

<FIG> are graphs illustrating the relationship between the deflection angle θ of the mirror unit <NUM> and the normalized difference Ev in the light detection units 4a and 4b, respectively.

The normalized difference Ev is defined by the following Formula <NUM>. <NUM>] <MAT> where in Formula <NUM>, Va and Vb denote the output voltages of the light detectors 54a and 54b, respectively, in each light detection unit <NUM>.

In Formula <NUM>, the numerator of the right side is the difference between Va and Vb. The denominator of the right side is the sum of Va and Vb, and is for generating a normalized difference Ev in which the numerator difference is normalized regardless of the type of the optical scanning device <NUM>.

By design, the light detection units 4a and 4b are expected to be disposed such that the centers of the index light spots 51a and 51b overlap the division line <NUM>, which serves as the boundary line of the light detectors 54a and 54b. However, in practice, due to manufacturing errors or the like, the light detection units 4a and 4b are inconveniently attached with the division line <NUM> deviated from the reflection direction of the index light spots 51a and 51b in some cases. In such a case, even if the deflection angle of the mirror unit <NUM> reaches the reflection angle of the twice reflected light L2, the Va - Vb, which is the difference under the condition of α1 = α2 = <NUM>°, inconveniently changes from <NUM> (zero) depending on the intensity of the once reflected light L1 and the twice reflected light L2.

However, Formula <NUM> of the normalized difference Ev under the condition of α1 = α2 = <NUM>° eliminates the influences by the difference in intensity between the twice reflected light L2 from the groove-shaped reflection part <NUM> and the once reflected light L1 from the flat reflection part <NUM>, thus making it possible to accurately detect the timing at which the deflection angle θ of the mirror unit <NUM> reaches the reflection angle of the twice reflected light L2.

This is because, although the normalized difference Ev of Formula <NUM> is not zero when the deflection angle θ reaches the reflection angle of the twice reflected light L2 (= index deflection angle ±<NUM>°), the normalized difference Ev of Formula <NUM> remains at the same level regardless of the intensities of the once reflected light L1 and the twice reflected light L2.

The method for detecting the deflection angle θ is not limited to the difference method of Formula <NUM>. The detection can be also performed based on the ratio of the outputs of the light detectors 54a and 54b (Va / Vb) in place of the difference.

<FIG> is a schematic diagram illustrating the relative positions of the scanning light spot <NUM> and the index light spot 51b and the light detectors 54a and 54b in the light detection unit 4b at P1 to P5 of <FIG>. Sc denotes the scanning direction of the scanning light spot <NUM>.

The following will describe the normalized difference Ev at each position of P1 to P5, assuming that the division line <NUM> is located at a position in the direction of ±<NUM>° of the normal emission angle γ, as with the case of <FIG>. In the following description, it is assumed that the division line <NUM> is located at a position in the direction of the emission angle γ = ±<NUM>°, which is the normal position, and there are no variations in the output characteristics of the light detectors 54a and 54b.

At P1, the scanning light spot <NUM> is in front of the light detection unit 4b in the scanning direction Sc. The index light spot 51b is located at a position where the center thereof overlaps the division line <NUM>. Therefore, each of the light detectors 54a and 54b receives the light amount of half of the index light spot 51b. Consequently, the normalized difference Ev = <NUM>.

At P2, the front end of the scanning light spot <NUM> enters the light detector 54a. The index light spot 51b is at the same position as that at P1. Therefore, the light detector 54a receives the half of the index light spot 51b and the front end portion of the scanning light spot <NUM>. Consequently, the normalized difference Ev is expressed as Ev > <NUM>.

At P3, the center of the scanning light spot <NUM> reaches a position where the center thereof overlaps the division line <NUM>. The front half of the scanning light spot <NUM> overlaps the light detector 54b. Consequently, the light amount of the index light spot 51b and the scanning light spot <NUM> is also divided into two equal parts by the division line <NUM>, leading to Ev = <NUM>. The deflection angle θ of the mirror unit <NUM> at this time is <NUM>°.

At P4, the center of the scanning light spot <NUM> enters the light detector 54b. Therefore, Ev < <NUM>.

At P5, in the scanning direction Sc, the scanning light spot <NUM> has the first half thereof positioned outside the light detection unit 4b and the latter half thereof remaining in the light detector 54b. Therefore, the normalized difference Ev is expressed as Ev < <NUM>, as illustrated by P5 in <FIG>.

When the scanning light spot <NUM> passes through the division line <NUM> of the light detection units 4a and 4b in the scanning direction Sc, the sign of the normalized difference Ev is reversed from positive to negative. On the other hand, when the scanning light spot <NUM> passes through the division line <NUM> of the light detection units 4a and 4b in the direction opposite to the scanning direction Sc, the sign of the normalized difference Ev is reversed from negative to positive.

The deflection angle detection unit <NUM> recognizes the timing at which the sign of the normalized difference Ev is reversed as the timing at which the deflection angle θ of the mirror unit <NUM> is ±<NUM>°.

The mirror unit <NUM> performs the reciprocating rotation about the rotation axis <NUM>, so that the scanning light spot <NUM> reciprocates to left and right on the scanning trajectory <NUM> in <FIG>. When the scanning light spot <NUM> travels from left to right on the scanning trajectory <NUM>, the deflection angle θ changes in an increasing direction. When the scanning light spot <NUM> travels from right to left on the scanning trajectory <NUM>, the deflection angle θ changes in a decreasing direction.

In the light detection unit 4a, the timing at which the normalized difference Ev of the light detection unit 4a is reversed from positive to negative is detected as the timing at which the scanning light spot <NUM> passes through the division line <NUM> of the light detection unit <NUM> from the outer side to the inner side. The timing at which the normalized difference Ev is reversed from negative to positive is detected as the timing at which the scanning light spot <NUM> passes through the division line <NUM> of the light detection unit <NUM> from the inner side to the outer side.

In the light detection unit 4b, the timing at which the normalized difference Ev of the light detection unit 4b is reversed from positive to negative is detected as the timing at which the scanning light spot <NUM> passes through the division line <NUM> of the light detection unit <NUM> from the inner side to the outer side. The timing at which the normalized difference Ev of the light detection unit 4b is reversed from negative to positive is detected as the timing at which the scanning light spot <NUM> passes through the division line <NUM> of the light detection unit <NUM> from the outer side to the inner side.

The deflection angle detection unit <NUM> constantly monitors the outputs of the light detection unit 4a and the light detection unit 4b. The deflection angle detection unit <NUM> sets the timing at which the light detection unit 4a reverses from positive to negative as t1 on a time axis, and then sets the timing at which the light detection unit 4b reverses from positive to negative as t2 on the time axis. The time difference t2 - t1 can be grasped as the time required for the deflection angle θ of the mirror unit <NUM> to change from -<NUM>° to + <NUM>°. On the other hand, the cycle of the reciprocating rotation of the mirror unit <NUM> about the rotation axis <NUM> and the distance between the light detection units 4a and 4b are fixed. Therefore, the scanning speed of the scanning light spot <NUM> is determined based on the time difference t2 - t1 and the distance, and further, a maximum deflection angle θ of the mirror unit <NUM> about the rotation axis <NUM> (i.e., the angle range in which the deflection angle θ changes or the deflection width of the scanning light spot <NUM>) can be detected based on the scanning speed.

<FIG> is a perspective view of the groove-shaped reflection part <NUM> having a plurality of longitudinal grooves <NUM>. The groove-shaped reflection part <NUM> has only one longitudinal groove <NUM>, so that the intensity of the index light spots 51a and 51b is low. On the other hand, the groove-shaped reflection part <NUM> includes the plurality of the longitudinal grooves <NUM>. As a result, the light receiving intensity of the index light spots 51a and 51b can be increased in the light detection units 4a and 4b.

On the other hand, the presence of the plurality of the longitudinal grooves <NUM> causes the twice reflected light L2 from each longitudinal groove <NUM> to interfere with each other. The interference effect intensifies the twice reflected light L2, thus making it possible to further increase the light receiving intensity of the index light spots 51a and 51b in the light detection units 4a and 4b.

Thus, a pitch Dp of the longitudinal grooves <NUM> (the interval of the longitudinal grooves <NUM> in the X-axis direction when the light deflector <NUM> is in a stationary state) is set according to the following Formula <NUM>. <NUM>] <MAT> where in Formula <NUM>, m denotes a natural number, λ denotes the wavelength of the original light La, and α1 and α2 are <NUM>° in the present embodiment.

The pitch Dp of the longitudinal grooves <NUM> in the X-axis direction is calculated according to Formula <NUM>. Consequently, the light detection unit <NUM> is located at a position where a plurality of twice reflected lights L2 from the groove-shaped reflection part <NUM> intensify each other, thus making it possible to increase the S/N ratio of an output of the light detection unit <NUM> and thereby to improve the accuracy of detecting the deflection angle θ.

Next, <FIG> is an explanatory diagram illustrating the preventive measures against the thrice reflected light L3. The measures against the thrice reflected light L3 will be described with reference to the groove-shaped reflection part <NUM> (<FIG>). The same measures can be applied to the groove-shaped reflection part <NUM> (<FIG>).

For the convenience of explanation, a first plane <NUM>, a second plane <NUM>, and a third plane <NUM>, which are parallel to each other, will be defined. The first plane <NUM> is a plane at a position where the longitudinal groove <NUM> opens at the front surface side of the light deflector <NUM> in the Z-axis direction. The flat reflection surface of the flat reflection part <NUM> is included in the first plane <NUM>. The third plane <NUM> is a plane that connects the valley bottoms of the plurality of longitudinal grooves <NUM> formed by V-grooves in the groove-shaped reflection part <NUM>.

The second plane <NUM> is set, as a division plane, at a position midway between the first plane <NUM> and the third plane <NUM> in the Z-axis direction. The inclined surfaces 42a and 42b are bisected into a front surface side inclined surface portion Fa and a back surface side inclined surface portion Fb with the second plane <NUM> as a boundary.

Da denotes the length of the front surface side inclined surface portion Fa in a cross section of the longitudinal groove <NUM>. Db denotes the length of the back surface side inclined surface portion Fb in a cross section of the longitudinal groove <NUM>. Dc denotes the dimension in the X-axis direction between an intersection line 61b and an intersection line 61a, which are adjacent to each other in the relationship of the negative side and the positive side in the X-axis direction in the cross section of the longitudinal groove <NUM>. Dd denotes the dimension in the X-axis direction between the intersection line 61a and the intersection line 61b, which are adjacent to each other in the relationship of the negative side and the positive side in the X-axis direction. De and Df denote the dimensions of the front surface side inclined surface portion Fa and the back surface side inclined surface portion Fb in the Z-axis direction (the depth direction of the longitudinal groove <NUM>).

The relationship of the following Formula <NUM> holds among Da to Df, where α1 = α2 = α applies.

<FIG> is a cross-sectional view of a groove-shaped reflection part <NUM> provided with measures against the thrice reflected light L3. An inclined surface <NUM> of a longitudinal groove <NUM> of the groove-shaped reflection part <NUM> is constructed by removing the back surface side inclined surface portion Fb from the inclined surfaces 42a and 42b of the longitudinal groove <NUM> of the groove-shaped reflection part <NUM> (<FIG>), leaving only the front surface side inclined surface portion Fa.

As with the plurality of longitudinal grooves <NUM> of the groove-shaped reflection part <NUM>, a plurality of the longitudinal grooves <NUM> of the groove-shaped reflection part <NUM> are aligned in parallel to the rotation axis <NUM> in the vertical direction. The length of the inclined surface <NUM> is set to Da (<FIG>). Each of the longitudinal grooves <NUM> has a valley side opening <NUM> on the rear surface side. A recess <NUM> is formed on the rear surface side of the groove-shaped reflection part <NUM>, and each of the valley side openings <NUM> is in common communication with the recess <NUM>.

As a result, in the groove-shaped reflection part <NUM>, of the original light La, a part of the original light La that is irradiated to the back surface side inclined surface portion Fb of the groove-shaped reflection part <NUM> (<FIG>) exits to the rear surface side of the mirror unit <NUM> from the valley side opening <NUM>. Therefore, in the groove-shaped reflection part <NUM>, the generation of the thrice reflected light L3 overlapping the twice reflected light L2 is prevented.

<FIG> illustrates the relationship between the deflection angle θ and the intensity of the twice reflected light L2 when the groove-shaped reflection part <NUM> of <FIG> is adopted. When there are a plurality of longitudinal grooves <NUM>, a plurality of twice reflected lights L2 from the plurality of the longitudinal grooves <NUM> interfere with each other, thus causing the intensity of the index light spot <NUM> in the light detection unit <NUM> to change according to the deflection angle θ, as illustrated in <FIG>.

Therefore, the controller <NUM> not only calculates the normalized difference Ev between the output Va of the light detector 54a and the output Vb of the light detector 54b (= Va - Vb) but also calculates a total Et of the output Va of the light detector 54a and the output Vb of the light detector 54b (= Va + Vb). Further, the deflection angle θ other than the deflection angle θ = ±<NUM>° (the deflection angle θ corresponding to each peak in <FIG>) can be also measured based on a total Q.

<FIG> presents graphs, each illustrating the relationship between the emission angle γ and the light intensity on the emission side at various deflection angles θ of the mirror unit <NUM>, the relationships having been found by experiments. Although the emission angle γ of the scanning light Lb increases as the deflection angle θ of the mirror unit <NUM> increases, the emission angle γ of the twice reflected light L2 is maintained constantly at the index deflection angle <NUM>°. Further, it can be seen that the emission angle γ can be detected over the entire deflection width Wb (<FIG>) of the scanning light Lb.

<FIG> presents graphs illustrating the experiment results of the comparison in the distribution of light intensity on the emission side with respect to predetermined deflection angles θ between the mirror unit <NUM> (the embodiment) and a comparative example. The comparative example uses a diffraction grating type mirror unit. It can be seen that the twice reflected light L2 is generated in the mirror unit <NUM>, whereas no noticeable diffracted light, such as second-order light, third-order light and so on, is generated in the comparative example.

<FIG> presents photographs illustrating the experiment results of <FIG>. It can be seen that the twice reflected light L2 appears at the index deflection angle in the mirror unit <NUM> (the embodiment), whereas no light appears at the index deflection angle in the comparative example (the diffraction grating type mirror unit).

<FIG> is a configuration diagram of an optical scanning device <NUM> provided with a two-axis (two-dimensional) scanning type light deflector <NUM>. As the two-axis scanning type optical scanning device, the two-axis scanning type light deflector <NUM> is provided therein.

The optical scanning device <NUM> differs from the optical scanning device <NUM> in that the optical scanning device <NUM> includes the light deflector <NUM> and a light detection unit <NUM> in place of the light deflector <NUM> and the light detection unit <NUM> of the optical scanning device <NUM>. The following will describe the light deflector <NUM> and the light detection unit <NUM>.

The light deflector <NUM> has the same configuration as a known two-axis piezoelectric light deflector (e.g., <CIT>) except for a mirror unit <NUM>. The mirror unit <NUM> will be described in detail later. The structure of the light deflector <NUM> will be briefly described.

The light deflector <NUM> includes the mirror unit <NUM>, torsion bars 131a and 131b, inner piezoelectric actuators 145a and 145b, a movable frame <NUM>, outer piezoelectric actuators 147a and 147b, and a fixed frame <NUM>.

A first rotation axis <NUM> and a second rotation axis <NUM> are both set on the front surface of the light deflector <NUM> and are orthogonal to each other at a center O of the mirror unit <NUM>. The first rotation axis <NUM> coincides with the center axis of the torsion bar <NUM>. When the light deflector <NUM> is stationary, the first rotation axis <NUM> and the second rotation axis <NUM> are in the Y-axis direction and the X-axis direction, respectively.

The inner piezoelectric actuator <NUM> torsionally vibrates the torsion bar <NUM> about the first rotation axis <NUM> at a resonant frequency. This causes the mirror unit <NUM> to perform reciprocating rotation about the first rotation axis <NUM> at a resonant frequency F1. The outer piezoelectric actuator <NUM> causes the movable frame <NUM> to perform reciprocating rotation about an axis parallel to the X-axis at a non-resonant frequency F2 (F2 < F1). Consequently, the mirror unit <NUM> performs reciprocating rotation about the second rotation axis <NUM>.

The mirror unit <NUM> will now be described in detail. Unlike the mirror unit <NUM>, the mirror unit <NUM> performs reciprocating rotation about the two axes, namely, the first rotation axis <NUM> and the second rotation axis <NUM>, but has the same structure as that of the mirror unit <NUM>. In other words, the mirror unit <NUM> has, on the front surface thereof, a flat reflection part <NUM> and a groove-shaped reflection part <NUM>, which are identical to the flat reflection part <NUM> and the groove-shaped reflection part <NUM>, respectively, of the mirror unit <NUM>.

In the optical scanning device <NUM>, the deflection angle θ of the mirror unit <NUM> about the first rotation axis <NUM> is detected by light detection units 104a and 104b. The light detection units 104a and 104b correspond to the light detection units 4a and 4b, respectively, of the optical scanning device <NUM>.

Whereas the light detection units 4a and 4b are formed to be rectangular, the light detection units 104a and 104b are formed to have a long narrow shape in the Y-axis direction. This is because the mirror unit <NUM> performs reciprocating rotation also about the second rotation axis <NUM>, so that the emission direction of the twice reflected light L2, which is fixed in the optical scanning device <NUM>, is displaced to the Y-axis direction in the light deflector <NUM>.

In the twice reflected light L2, the central portion in the displacement direction approaches inward in the X-axis direction with respect to both ends in the displacement in the Y-axis direction. This is reflected, and the division line of the light detection units 104a and 104b extends inward in the X-axis direction with respect to both ends in the central portion in the Y-axis direction.

<FIG> is a configuration diagram of an optical scanning device <NUM> capable of detecting the deflection angle of a mirror unit <NUM> about a second rotation axis <NUM>. In the optical scanning device <NUM>, only a different aspect from the optical scanning device <NUM> will be described.

A groove-shaped reflection part <NUM> of the mirror unit <NUM> has been rotated by <NUM>° clockwise with respect to a center O of the mirror unit <NUM> of the optical scanning device <NUM>. As a result, the twice reflected light L2 as the index light from the groove-shaped reflection part <NUM> is displaced in the X-axis direction while being emitted from the light deflector <NUM> to both sides in the Y-axis direction for the reciprocating rotation of the mirror unit <NUM> about the first rotation axis <NUM>.

Thus, light detection units 164a and 164b that detect the twice reflected light L2 are formed to have the long narrow shape in the X-axis direction. Further, division lines <NUM> of the light detection units 164a and 164b extend such that the central portions thereof in the X-axis direction are on the inner side in the Y-axis direction with respect to both end portions.

As with the light detection units 4a and 4b of the optical scanning device <NUM>, the light detection units 164a and 164b detect the normalized difference Ev and a subtraction difference Es of the output voltages Va and Vb of the light detectors 54a and 54b divided from the light detection units 164a and 164b, respectively, by division lines <NUM>. In the optical scanning device <NUM>, the normalized difference Ev and the subtraction difference Es correspond to the deflection angle of the mirror unit <NUM> about the second rotation axis <NUM>, so that the deflection angle of the mirror unit <NUM> about the second rotation axis <NUM> is detected based on the normalized difference Ev and the subtraction difference Es.

In the embodiment, the difference Va - Vb (refer to the aforementioned Formula <NUM>) is used to detect the deflection angle θ of the mirror unit <NUM> about the first rotation axis (e.g., the rotation axis <NUM>) based on the two outputs (e.g., Va and Vb) of the first and the second light detectors (e.g., 4a and 4b). In the present invention, the deflection angle θ can be detected based on the comparison of the two outputs (e.g., Va / Vb as the ratio of the two outputs) in place of the difference.

In the embodiment, the index deflection angle as the deflection angle θ of the mirror unit <NUM> associated with the traveling direction of index light (e.g., the twice reflected light L2) is set to <NUM>°. The index deflection angle in the present invention can be changed to a numeric value other than <NUM>°. The index deflection angle can be changed by, for example, changing the tilt angles α1 and α2 of the pair of inclined surfaces 42a and 42b in <FIG>.

The first rotation axis in the present invention corresponds to the rotation axis <NUM> and the first rotation axis <NUM> in the embodiment, and the second rotation axis corresponds to the second rotation axis <NUM>. In the present invention, the second rotation axis <NUM> of the embodiment can be used as the first rotation axis.

The first actuator of the present invention corresponds to the piezoelectric actuator <NUM> and the inner piezoelectric actuator <NUM>. The second actuator of the present invention corresponds to the outer piezoelectric actuator <NUM>. The first actuator and the second actuator of the embodiment are both piezoelectric, but the first actuator and the second actuator of the present invention may alternatively be electromagnetic coil type or electrostatic type actuators.

A specific structure example of an electromagnetic coil type actuator is described in detail in the following literature:
"<NPL>. " In addition, a specific structure example of the aforementioned electrostatic type actuator is described in detail in the following literature: "<NPL>.

In the light deflector <NUM> or <NUM>, the groove-shaped reflection part <NUM> or <NUM> is provided only at the central portion, and the light detection unit <NUM> or <NUM> is provided at both sides of the light deflector <NUM> or <NUM>. In the present invention, the deflection angle θ of the mirror unit <NUM> or <NUM> can be detected also by providing the groove-shaped reflection part <NUM> or <NUM> only at one side in the X-axis direction with respect to the center O, and providing the light detection unit <NUM> or <NUM> only at the other side in the X-axis direction with respect to the light deflector <NUM> or <NUM>. Alternatively, the groove-shaped reflection part <NUM> or <NUM> may be provided at both sides, one side and the other side, with respect to the center O of the mirror unit <NUM> so as to cause the light detection unit <NUM> at the other side to receive the twice reflected light L2 from the groove-shaped reflection part <NUM> or <NUM> at one side, and to cause the light detection unit <NUM> at one side to receive the twice reflected light L2 from the groove-shaped reflection part <NUM> or <NUM> at the other side.

In a SOI active layer that constitutes the substrate layer of each of the light deflectors <NUM> and <NUM>, the main surface thereof has Miller index (<NUM>), and the inclined surface <NUM> has Miller index (<NUM>). In a light deflector of the present invention, the main surface of a silicon crystal layer of a substrate may have Miller index (<NUM>) and the inclined surface <NUM> may have Miller index (<NUM>).

The flat reflection parts <NUM> and <NUM>, and the groove-shaped reflection parts <NUM>, <NUM>, 89a, 89b and <NUM> are formed as a mirror surface layer covering the common substrate layer of the mirror units <NUM> and <NUM>. The mirror surface layer is composed of, for example, a silicon crystalline surface, a metal reflective film or a dielectric multilayer film.

Claim 1:
An optical scanning device (<NUM>, <NUM>, <NUM>) comprising:
a light source (<NUM>) which emits light (La);
a light deflector (<NUM>, <NUM>) having a mirror unit (<NUM>, <NUM>) which includes: on a front surface side, a flat reflection part (<NUM>, <NUM>) that emits incident light entering from the light source (<NUM>) as scanning reflection light (Lb), and a first actuator (32a-32d, 145a,145b) that rotates the mirror unit (<NUM>, <NUM>) in a reciprocating manner about a first rotation axis (<NUM>, <NUM>) ; wherein
the mirror unit (<NUM>, <NUM>) further includes, on the front surface side, a groove-shaped reflection part (<NUM>, <NUM>, <NUM>, <NUM>) having a longitudinal groove (<NUM>, <NUM>) that extends in parallel to the first axis (<NUM>, <NUM>) and that has a pair of inclined surfaces (42a,42b,72a,72b) facing each other such that a groove width decreases from the front surface side to a back surface side, and which reflects the incident light a total of twice, once on each inclined surface and emits the reflected incident light as index light (Lc), and
the optical scanning device (<NUM>, <NUM>, <NUM>) further comprises:
a light detection unit (4a, 4b) which is disposed on a scanning trajectory (<NUM>) of a scanning light spot (<NUM>) of the scanning reflection light (Lb) and at a light reception position of an index light spot (51a, 51b) of the index light (Lc), and is divided into a first light detector (54a) and a second light detector (54b) by a division line (<NUM>) that divides the index light spot (51a, 51b) in a scanning direction of the scanning reflection light (Lb); and
a deflection angle detection unit (<NUM>) which detects a first deflection angle as a deflection angle of the mirror unit (<NUM>, <NUM>) about the first rotation axis (<NUM>, <NUM>) based on comparison between an output of the first light detector (54a) and an output of the second light detector (54b).