Oscillator device, method of driving the same, optical deflector and image display device using the same

An oscillator device includes a first oscillator, a second oscillator configured to support the first oscillator for torsional rotation about a first rotational axis, through a first torsion spring, a supporting member configured to support the second oscillator for torsional rotation about a second rotational axis, through a second torsion spring, the second rotational axis having a predetermined angle with respect to the first rotational axis of the first oscillator, a coil disposed in relation to the second oscillator, an electrical current applying member configured to apply an electrical current to the coil, and a magnetic field generating member configured to apply a magnetic field to the coil. The coil is localized in at least one of zones of the second oscillator being quartered by extension lines of the first and second rotational axes.

This application claims priority from Japanese Patent Application No. 2007-039072, filed Feb. 20, 2007, which is hereby incorporated by reference herein.

FIELD OF THE INVENTION AND RELATED ART

This invention relates to an oscillator device having a plurality of oscillators, a method of driving the same, an optical deflector, and an image display unit using such an optical deflector. More particularly, the invention concerns an optical deflector that can be produced based on micromechanics techniques, a method of driving the same, and an image display unit using the deflector.

Optical deflectors are used to deflect a laser beam, for example. A galvano mirror is an example of a scanning mirror for scanningly deflecting a laser beam, and it is driven based on a driving principle such as follows.

When a movable coil disposed in a magnetic field is electrified, an electromagnetic force is produced due to the interaction of the electrical current and the magnetic flux, and a torque proportional to the electrical current is produced. The movable coil rotates by an angle at which this torque and a spring force are balanced. Through this movable coil, an indicating needle is oscillated and, based on this, the presence/absence or magnitude of the electrical current of the movable coil is detected. The scanning mirror, described above, is based on this principle, and a reflection mirror is provided in substitution for the needle, upon the shaft which rotates together with the movable coil.

Furthermore, there are optical deflectors that can be manufactured by using micromachining techniques, based on semiconductor manufacturing techniques, for producing a minute machine integrally on a semiconductor substrate. For example, K. E. Petersen, et al., have proposed a torsional scanning mirror made of Si (see IBM J. RES. DEVELOP., VOL. 24, No. 5, 9, 1980, pages 631-637). This optical deflector is such as shown inFIG. 22, and a mechanical moving element3comprises a mirror3aas an optical deflection plate and a beam-like structure3bfor supporting the mirror3a. Based on the electrostatic attraction that is produced by applying a drive voltage between the mirror3aand a fixed electrode2, which is formed on a base plate, a torsion moment is applied to the beam3b, to cause torsional rotation of the beam3b, thereby to change the deflection angle of the mirror3a.

On the other hand, a scanner10, as shown inFIG. 23, having such a structure that a mirror described above is disposed for deflective rotation around dual axes, has been proposed. (See U.S. Pat. No. 5,912,608.) In this scanner, a movable plate (movable mirror)12B, having a mirror16, is supported by gimbals12A through two torsion bars13B, and the gimbals12A is supported by a base plate11through two torsion bars13A. The rotational axes of the movable mirror and the gimbals are orthogonal to each other.

SUMMARY OF THE INVENTION

Driving coils15A and15B are formed at the peripheral portion of the movable mirror12B and the gimbals12A having such a structure, and permanent magnets4and5are placed in the same plane, while sandwiching the movable mirror and the gimbals therebetween in one diagonal direction, by which the movable mirror and the gimbals are driven.

The abovementioned galvano mirror requires a mechanically wound movable coil and a large-size yoke for producing a magnetic field. Furthermore, in the actuator shown inFIG. 23, the permanent magnets4and5are disposed in the same plane, while sandwiching the movable mirror and the gimbals therebetween. Therefore, a reduction in size is difficult to achieve.

In accordance with an aspect of the present invention, an oscillator device comprises a first oscillator, a second oscillator configured to support the first oscillator for torsional rotation about a first rotational axis, through a first torsion spring, a supporting member configured to support the second oscillator for torsional rotation about a second rotational axis, through a second torsion spring, the second rotational axis having a predetermined angle with respect to the first rotational axis of the first oscillator, a coil disposed in relation to the second oscillator, an electrical current applying member configured to apply an electrical current to the coil, and a magnetic field generating member configured to apply a magnetic field to the coil, wherein the coil is localized in at least one of zones of the second oscillator being quartered by extension lines of the first and second rotational axes.

In accordance with another aspect of the present invention, an image display device comprises a light source, an optical deflector as mentioned above and having an oscillator device, and a surface to be irradiated with light, wherein light from the light source is deflected by the oscillator device, and at least a portion of the deflected light is incident on the surface to be irradiated.

In accordance with a further aspect of the present invention, a method of driving an oscillator device is characterized in that the electrical current signal is comprised of a first driving current signal of a periodic signal having a first frequency adapted to torsionally rotate the first oscillator relative to the second oscillator, and a second driving current signal of a periodic signal having a second frequency adapted to torsionally rotate the second oscillator relative to the supporting member, and electrical currents are applied to the first coil to the fourth coil in the manner that the amount of electrical current change of the first coil to the fourth coil in response to the first driving current signal is the same, and it is taken as a current change amount1, while the amount of electrical current change of the first coil to the fourth coil in response to the second driving current signal is the same, and it is taken as a current change amount2, and that the amount of electrical current change of the first and second coils is taken as an addition of the current change amount1and the current change amount2, while the amount of electrical current change of the third and fourth coils is taken as a subtraction of the current change amount1and the current change amount2.

In accordance with the present invention, in an oscillator device, such as an optical deflector of a dual-axis driving type based on a gimbals structure, only a magnetic field producing member, such as a permanent magnet, is disposed on a surface opposed to an electrical coil. Therefore, a reduction in size is very easy to accomplish.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will hereafter be explained in greater detail, with reference to more specific embodiments. The embodiments to be described below concern an oscillator device of the present invention, which is applied to an optical deflector of a dual-axis drive type. However, the oscillator device of the present invention can be applied to any device where such a structure is required.

A first embodiment of the present invention will be explained with reference to several drawings.

FIG. 1AandFIG. 2Aare top plan views, which show the structure of a first embodiment of an optical deflector of the present invention, as well as a modified example of the same.FIG. 1Bis a sectional view taken along a line A-A, showing the structure of the embodiment ofFIG. 1A.FIG. 2Bis a sectional view based onFIG. 2A, illustrating the structure of the modified example ofFIG. 2A.FIG. 3is a diagram for explaining the magnetic field direction that the electrical coil of the optical deflector shown inFIG. 1AandFIG. 2Aproduces.FIG. 4A-FIG.4C are diagrams for explaining an electrical current signal.FIG. 5B-FIG.5D are diagrams for explaining the driving method, using the section taken along a broken line A-A′ inFIG. 5A.

The embodiment shown inFIG. 1AandFIG. 1Bcomprises a movable mirror102, which is a first oscillator, a gimbals101, which is a second oscillator, a supporting member104, electrical coils106and107disposed on the gimbals101, and a permanent magnet110, which is a magnetic field producing member. An optical deflection element, such as a mirror, is provided on the movable mirror102. The gimbals101supports the movable mirror102through a torsion bar103of a beam-like shape, which is a first torsion spring, for torsional rotation about a first rotational axis (shown at a broken line B-B′). The supporting member104supports the gimbals101through a torsion bar105of a beam-like shape, which is a second torsion spring, for torsional rotation about a second rotational axis (shown at a broken line A-A′).

The permanent magnet110applies a magnetic field to the electrical coils106and107so as to torsionally rotate the movable mirror102relative to the gimbals101, and to torsionally rotate the gimbals101relative to the supporting member104. For the magnetic field generating member, an electromagnetic coil may be used.

Furthermore, the coils106and107do not wind around the movable mirror102, and they are localized in at least one (two in this example) of the zones, which are quartered by the extension lines of the first and second rotational axes. More specifically, in a two-dimensional optical deflector having a gimbals structure mentioned above, the coils106and107are disposed on the gimbals101in the manner that their center positions are off the extension lines of the first and second torsion bars103and105, respectively. The electrical coils106and107have their windings wound in opposite directions.

The modified example shown inFIG. 2AandFIG. 2Bis different from the embodiment ofFIG. 1AandFIG. 1Bin the following points.

In this modified example, the magnet110is disposed so that one of the N pole and the S pole is placed on the magnetic field, which approximately passes through the center of the coil106within the magnetic field that the coil106generates, and that the other magnetic pole is placed on the magnetic field, which approximately passes through the center of the electrical coil107within the magnetic fields that the coil107forms. It is magnetized in the direction shown inFIG. 2B. More specifically, the S pole is at the side opposed to the electrical coil106, and the N pole is at the side opposed to the electrical coil107. Furthermore, the coils106and107have their windings wound in the same direction.

The structure and function of the present embodiment will be explained further. In this embodiment, the gimbals101, movable mirror102, first torsion bar103, supporting member104and second torsion bar105can be formed integrally by performing a removal processing to monocrystal silicon. An insulating layer is formed between the electrical coils106and107and the gimbals101, so that they are electrically isolated from each other. Furthermore, the electrical wirings for the coils106and107extend along the second torsion bar105, where an insulating layer (not shown) is formed, and then they are connected to a contact pad108provided on the supporting member104. There is an intermediate insulating layer109at the junction between the innermost winding of the coils106and107and the connecting wiring, to avoid electrical connection with the outer windings of the coil. The intermediate insulating layer109may be made of polyimide, for example.

Permanent magnets110are disposed at positions opposed to the electrical coils106and107, which are formed on the gimbals101, as described above. A plurality of electrical coils may be used and, in this embodiment, as described above, two permanent magnets are disposed in zones which are in a diagonal positional relationship with each other, sandwiching the first torsion bare103. When plural electrical coils are used, it is necessary to consider the matching with the magnetic poles of the permanent magnets110placed opposed to the electrical coils106and107. In a case where two permanent magnets are disposed at opposite positions sandwiching the first torsion bar103, as shown inFIG. 1A, and the electrical coils106and107have opposite winding directions, the opposite placed permanent magnets110should be disposed so that they have the same magnetic pole direction (FIG. 1B).

On the other hand, if two permanent magnets are disposed at opposite directions sandwiching the first torsion bar103, as shown inFIG. 2A, and they have the same coil winding direction, the oppositely placed permanent magnets110should be disposed so that they have opposite magnetic pole directions (seeFIG. 2B).

As shown inFIG. 2A, if the electrical coils106and107have the same winding direction, only one permanent magnet110may be used, and, on that occasion, it may be disposed such as shown inFIG. 2B. In this case, it is disposed so that the magnetic poles are opposite to the electrical coils106and107, respectively.

A spacer111is provided between the electrical coils106and107, and the permanent magnet110. Thus, even when the movable mirror102and the gimbals101torsionally rotate, the permanent magnet111and the movable mirror102do not interfere with each other. The supporting member104and the spacer111, as well as the spacer111and the supporting base plate115of the permanent magnet110, may be fixed together, respectively, by using an adhesive (not shown).

In the structure described above, when the gimbals101is angularly displaced by the second torsion bar105relative to the supporting member104, the movable mirror102coupled to the gimbals101through the first torsion bar103angularly displaces in the same direction as the gimbals101. More specifically, the movable mirror102is angularly displaced by the first torsion bar103relative to the gimbals104, and is angularly displaced by the second torsion bar105relative to the supporting member104. For example, by disposing the first torsion bar103and the second torsion bar105in approximately orthogonal directions, and by scanning the light from a light source by the movable mirror102, a two-dimensional optical scan is accomplished.

The movable mirror102and the gimbals101are angularly displaced by the first and the second torsion bars relative to the gimbals and the supporting member, respectively, based on the electromagnetic force working between the permanent magnet and the magnetic field generated by the application of the current signals to the electrical coils106and107. For example, if an electrical current1is applied in the direction of an arrow using the structure shown inFIG. 1A, a magnetic field1and a magnetic field2, such as shown inFIG. 3, are generated in the electrical coils106and107, respectively. Here, the permanent magnet110disposed opposed to the electrical coil106and the magnetic field1(it is in the direction toward the front of the sheet of the drawing) pull each other based on the electromagnetic force. On the other hand, the permanent magnet110and the magnetic field2(it is in the direction toward the back of the sheet of the drawing) repulse each other.

Here, an example of drive current signals applied to the electrical coils, as well as torsional rotation of the movable mirror102and the gimbals101, will be explained usingFIG. 4. The signals to be applied to the electrical coils106and107are an electrical current signal provided by superposing a first driving current signal and a second driving current signal on one another. The first driving current signal is one for torsionally rotating the movable mirror102(first oscillator) relative to the gimbals101(second oscillator) through the first torsion bar103. The second driving current signal is one for torsionally rotating the gimbals101(second oscillator) relative to the supporting member104.

For example, the first driving current signal may be a sinusoidal wave having a frequency approximately the same as the torsion resonance frequency of the movable mirror102and the first torsion bar103, and the frequency may be set to 20 kHz, for example (seeFIG. 4A). If only the first driving current signal is applied to the electrical coils106and107, as shown inFIG. 5B, the movable mirror102makes a torsional resonance motion relative to the gimbals101, through the first torsion bar103. On the other hand, the second driving current signaling may be a current signal, for example, by which the angular displacement of the gimbals101is based on a sawtooth wave, and the frequency may be set to 60 Hz, for example (seeFIG. 4B). If only the second driving current signal is applied to the electrical coils106and107, as shown inFIG. 5C, the gimbals101makes an angular displacement relative to the supporting member104through the second torsion bar105. The driving signal has a waveform provided by superposing the first driving current signal and the second driving current signal, shown inFIG. 4C, one on another. If the driving current signal is applied to the electrical coils106and107, as shown inFIG. 5D, the movable mirror102torsionally rotates relative to the gimbals101, while the gimbals torsionally rotates relative to the supporting member104.

As described above, since the frequencies of the first driving current signal and the second driving current signal are sufficiently different, torsional motions of the movable mirror102and the gimbals101are activated without mixture. Furthermore, in the above-described structure, for accurate and well-balanced torsional rotations, as described, the centroids of the oscillators (movable mirror102and gimbals101) are placed approximately at the point of intersection of the above-described two rotational axes. Then, because of localized configuration of the electrical coils, as described above, an electromagnetic force is generated effectively around each rotational axis, and oscillation of a desired oscillator is activated.

With the optical deflector of the structure described above, since the permanent magnet110is placed only on the plane opposed to the electrical coils106and107, a reduction in size is easy to accomplish. Furthermore, only by applying an electrical current signal to the electrical coil formed on the gimbals101, two-dimension angular displacement of the movable mirror102is accomplished. Thus, there is no need to provide a driving member, such as an electrical coil, on the movable mirror102, and thus, the desired surface flatness of the movable mirror102can be maintained.

A second embodiment of the present invention will be explained below.

The present embodiment concerns an optical deflector having a gimbals structure shown inFIG. 6andFIG. 7.FIG. 6is a top plan view that illustrates the structure of the optical deflector of the present embodiment, andFIG. 7is a sectional view of the optical deflector taken along a line A-A′ ofFIG. 6. The present embodiment uses only one localized electrical coil510.

In this embodiment, the optical deflector comprises an SOI substrate having an insulating layer501sandwiched between first and second silicon layers502and503. The thickness of the first silicon layer502is 100 μm, and the thickness of the second silicon layer503is 250 μm. The movable mirror504, gimbals505, first torsion bar506, second torsion bar507and supporting member508are formed by performing a removal processing to the first silicon layer502of the SOI substrate. There is a through-hole509formed in the second silicon layer503, such that rotational motion of the movable mirror504and the gimbals505is not disturbed. The supporting member508is fixed to a supporting frame514, which is formed by the second silicon layer503, while sandwiching the insulating layer501therebetween. The supporting frame514also functions as a spacer.

In the present embodiment, as well, the gimbals505supports the movable mirror504through the first torsion bar506, for torsional rotation. On the other hand, the supporting member508supports the gimbals505through the second torsion bar507, for torsional rotation. The electrical coil510, whose center position is off the extension lines of the first and second torsion bars, is provided on the gimbals505, on which an insulating layer (not shown) is formed. The electrical wiring of the electrical coil510extends along the second torsion bar507having an insulating layer (not shown) formed thereon, and it is connected to a contact pad511on the supporting member508. There is an intermediate insulating layer512at the junction between the innermost winding of the coil510and the connecting wiring, to avoid electrical connection with outer windings of the coil510. The intermediate insulating layer109may be made of polyimide, for example. The permanent magnet513is disposed on the supporting base plate515, at a position opposed to the electrical coil510.

In this case, as well, the movable mirror504and the gimbals505are angularly displaced relative to the gimbals and the supporting member, respectively, by the first and second torsion bars506and507, respectively, based on the electromagnetic force, which works between the magnetic field produced by the application of an electrical current signal to the electrical coil510and the magnetic field of the permanent magnet513.

A driving current1of a sinusoidal wave is applied to the electrical coil510, so as to produce angular displacement of the movable mirror504relative to the gimbals505. The frequency of this sinusoidal wave is set at the torsion resonance frequency of the movable mirror504and first torsion bar506with respect to the gimbals505. With this arrangement, the movable mirror504produces angular displacement motion having an angular displacement quantity based on a sinusoidal wave, relative to the gimbals505. Furthermore, an electrical current signal2of a sawtooth waveform is applied to the electrical coil510, so as to make gimbals505produce angular displacement motion relative to the supporting member508. This drive frequency is set to 60 Hz. Here, the angular displacement of the gimbals505shows a sawtooth-waveform. If only the current signal2is applied to the electrical coil510, since the movable mirror504is coupled to the gimbals505through the first torsion bar506, it performs an angular displacement movement together with the gimbals and through the second torsion bar507, relative to the supporting member508. Furthermore, by superposing the current signal1and current signal2on one another and applying it to the electrical coil501, two-dimensional angular displacement of the movable mirror504relative to the supporting member508is accomplished.

In the optical deflector of the structure described above, since only one permanent magnet513is placed at a surface opposed to a single electrical coil510, a reduction in size is enabled. Furthermore, two-dimensional angular displacement of the movable mirror504is accomplished only by applying a current signal to one electrical coil510formed on the gimbals505. The remaining features are similar to those of the first embodiment.

A third embodiment of the present invention will be explained.

The present embodiment is an example of an optical deflector having a gimbals structure, shown inFIG. 8A-FIG.8C.FIG. 8Ais a top plan view that illustrates the structure of the optical deflector of the present embodiment, andFIG. 8Bis a bottom view wherein some structural components are not shown.FIG. 8Cis a sectional view of this optical deflector, taken along a line B-B′.FIG. 9andFIG. 10are top plan views, which show two disposition examples of permanent magnets, wherein some structural components are not shown.FIG. 11A-FIG.11D andFIG. 12A-FIG.12D are diagrams for explaining a driving method of the present embodiment.FIG. 13A-FIG.13F are diagrams for explaining driving current signals. Furthermore,FIG. 14AandFIG. 14Bare diagrams for explaining a two-dimensional scan of the optical deflector of the present embodiment, andFIG. 15AandFIG. 15Bare diagrams for explaining a driving circuit, which is a current applying member of the present embodiment.

In this embodiment, the gimbals601supports the movable mirror602through the first torsion bar603, for torsional rotation. On the other hand, supporting member604supports the gimbals601through the second torsion bar605, for torsional rotation. The gimbals601, movable mirror602, first torsion bar603, supporting member604and second torsion bar605can be formed integrally by performing a removal processing to monocrystal silicon. As shown inFIG. 8A, the first and second electrical coils606and607are so disposed on the top surface (one surface) of the gimbals601that their center positions are off the extension lines of the first and second torsion bars. Furthermore, as shown inFIG. 8B, the third and fourth electrical coils609and610are so disposed on the bottom surface of the gimbals601(the other surface) that their center positions are off the extension lines of the first and second torsion bars. As a matter of course, a suitable intermediate insulating layer may be provided, and all four electrical coils may be placed at the same surface of the gimbals601.

An insulating layer is formed between each electrical coil and the gimbals601. Furthermore, the electrical coils606and607are connected electrically. Further, the opposite end portions extend along the top surface of the second torsion bar605having an insulating layer (not shown) formed thereon, and are connected to contact pads608on the supporting member604. The electrical coils609and610, as well, are connected electrically, and the opposite end portions extend along the bottom surface of the second torsion bar605having an insulating layer (not shown) formed thereon, and are connected to contact pads611on the supporting member604.

There is an intermediate insulating layer612at the junction between the innermost winding of the coils606and607and the connecting wiring, to avoid electrical connection with outer windings of the coil. A similar intermediate insulating layer613is provided on the coils609and610. These intermediate insulating layers612and613may be made of polyimide, for example.

A permanent magnet614is disposed at a position opposed to the electrical coils formed on the gimbals601. The electrical coils are disposed at four corners of the gimbals601. The orientation of the magnetic poles of the permanent magnet614placed opposed to the electrical coils should be determined while taking into account the matching with the winding direction of the electrical coils.

As shown inFIG. 8, of the four corners of the gimbals601, the electrical coil606and the electrical coil607are placed in a pair of zones, of the zones quartered by the extension lines of the first and second torsion bars, which pair are in a diagonal positional relationship with each other. On the other hand, the electrical coil609and the electrical coil610are placed in another pair of zones, of the quartered zones, which pair are in a diagonal positional relationship with each other. In the structure ofFIG. 8, the electrical coil606and the electrical coil607have opposite winding directions, and the electrical coil609and the electrical coil610, as well, have opposite winding directions. In this case, the permanent magnet614disposed opposed to the electrical coil606and the permanent magnet614disposed opposed to the electrical coil607are disposed so that they have the same magnetic pole direction. Also, the permanent magnet613disposed opposed to the electrical coil609and the permanent magnet613disposed opposed to the electrical coil610are disposed so that they have the same magnetic pole direction (FIG. 9).

InFIG. 9, all the permanent magnets614are placed with their N pole exposed. However, since it is sufficient that the permanent magnets614at the diagonally opposed corners have the same magnetic pole direction, the permanent magnets614at different (non-diagonal) corner positions may have different magnetic pole directions. In the case of the electrical coil disposition shown inFIG. 8AandFIG. 8B, the following is an example, other than the disposition example of the permanent magnets shown inFIG. 9.

Even one permanent magnet, such as shown inFIG. 10, may be used (while the N pole is exposed here, the S pole may be exposed). Alternatively, two permanent magnets may be disposed in parallel to each other, with their magnetization directions extending oppositely. The magnetic pole orientation and disposition of the permanent magnets, as well as the coil winding direction, can be chosen from various possible examples. Any combination may be chosen if it enables the operation to be described later.

In the present embodiment, as well, a spacer615is placed between the electrical coil and the permanent magnet614. When the movable mirror602and the gimbals601make torsional rotation, the permanent magnet614and the movable mirror602do not interfere with each other. The supporting member604and the spacer615, as well as the spacer615and the supporting base plate616of the permanent magnet614, may be fixed together, respectively, by using an adhesive (not shown).

The movable mirror602and the gimbals601are angularly displaced by the first and the second torsion bars relative to the gimbals601and the supporting member604, respectively, based on the electromagnetic force working between the permanent magnet614and the magnetic field generated by the application of the current signals to the electrical coils.

The function and operation of the present embodiment will be explained.

In the present embodiment, shown inFIG. 8, when an electrical current2and an electrical current3are applied in the positive direction shown by an arrow, magnetic fields1-4, such as shown inFIG. 11A, are generated in the electrical coils606,607,609and610. Here, the permanent magnets614placed at the positions opposed to the electrical coils and the magnetic fields1and4pull each other due to the electromagnetic force. Furthermore, the permanent magnets614and magnetic fields2and3repulse each other. Thus, as shown inFIG. 11C. a torsional rotational force in the direction of an arrow around the axis of the first torsion bar603acts on the movable mirror601and the gimbals602, so that they are angularly displaced. For a similar reason, when electrical currents2and3are applied in a direction opposite to the arrow, magnetic fields1-4, such as shown inFIG. 11B, are generated, and a torsional rotation force in the direction opposite to that shown inFIG. 11Cacts to cause angular displacement, as shown inFIG. 11D.

Furthermore, in this embodiment, when the electrical current2is applied in the direction of the arrow, while the electrical current3is applied in the direction opposite to the arrow, magnetic fields1-4, such as shown inFIG. 12A, are generated in the electrical coils606,607,609and610. Here, the permanent magnets614placed at positions opposed to the electrical coils, and the magnetic fields1and3, pull each other due to the electromagnetic force and, on the other hand, the permanent magnets and the magnetic fields2and4repulse each other. Thus, as shown inFIG. 12C, a torsional rotational force in the direction of an arrow around the axis of the second torsion bar605acts on the movable mirror601and the gimbals602, so that they are angularly displaced. For a similar reason, when electrical current2is applied in the opposite direction to the arrow, while electrical current3is applied in the positive direction of the arrow, magnetic fields1-4, such as shown inFIG. 12B, are generated, and a torsional rotational force in the direction opposite to that shown inFIG. 12Cacts, to cause an angular displacement, as shown inFIG. 12D.

Here, an example of the driving signal will be explained, with reference toFIG. 13.

The signals to be applied to the electrical coils106and107are an electrical current signal provided by superposing a first driving current signal and a second driving current signal on one another. The first driving current signal is one for torsionally rotating the movable mirror601(first oscillator) relative to the gimbals602(second oscillator) through the first torsion bar. The second driving current signal is one for torsionally rotating the gimbals602(second oscillator) relative to the supporting member604.

In the embodiment shown inFIG. 8, the first driving current signal concerns a case where the electrical currents2and3are applied in the positive direction of an arrow, or in the opposite direction. The second driving current signal concerns a case where one of the electrical currents2and3is applied in the positive direction of the arrow, while the other is applied in the opposite direction. If the first driving current signal or the second driving current signal changes periodically, the first driving current signal corresponds to the same-phase electrical current component (FIG. 13AandFIG. 13B) of the current2and current3, and the second driving current signal corresponds to the opposite-phase current component of the current2and current3(FIG. 13CandFIG. 13D).

Then, the first driving current signal may be a sinusoidal wave having a frequency approximately the same as the torsion resonance frequency of the movable mirror and the first torsion bar, and the frequency may be set to be 20 kHz, for example (seeFIG. 13A). If only the first driving current signal is applied to the electrical coils, as shown inFIG. 11, the movable mirror602makes torsional resonance motion relative to the gimbals601, through the first torsion bar103. On the other hand, the second driving current signal may be a current signal, for example, by which the angular displacement of the gimbals is based on a sawtooth wave, and the frequency may be set to be 60 Hz, for example (seeFIG. 13CandFIG. 13D). If only the second driving current signal is applied to the electrical coils, as shown inFIG. 12, the gimbals601makes an angular displacement relative to the supporting member604through the second torsion bar605.

The driving signal has a waveform provided by superposing the first driving current signal and the second driving current signal, shown inFIG. 13EandFIG. 13F, on one another. Here, as shown inFIG. 14AandFIG. 14B, the movable mirror602torsionally rotates relative to the gimbals601, while the gimbals601torsionally rotates relative to the supporting member604.

The circuitry shown inFIG. 13for applying an electrical current may be an H bridge circuit (FIGS. 15A and 15B), for example. The H bridge circuit may comprise transistors701and702for connecting the end node (contact pad) of the electrical coil to the high-voltage side, and transistors703and704for connecting the end node (contact pad) of the electrical coil to the low voltage side. The direction and magnitude of the electrical current flowing through the coil can be adjusted by the operation of the transistors701-704. For example, as shown inFIG. 15A, if the transistor701is connected to the high-voltage side and the transistor704is connected to the low voltage side, the electrical current of the electrical coil increases in the direction of the arrow. On the other hand, as shown inFIG. 15B, if the transistor703is connected to the low voltage side and the transistor702is connected to the high-voltage side, the electrical current of the electrical coil increases in the opposite direction to the case ofFIG. 15A. Thus, by changing the rate of time inFIG. 15AandFIG. 15B, the direction and magnitude of the electrical current flowing through the coil can be adjusted. In the embodiment shown inFIG. 8, an H bridge circuit, shown inFIGS. 15A and 15B, may be connected to the contact pads608and611.

A modified example of the optical deflector having a gimbals structure shown inFIG. 8may be a structure wherein the electrical coils606and607and the electrical coils609and610are not electrically connected to each other. In such a structure, an H bridge circuit shown inFIGS. 15A and 15Bmay be provided at each end node of the electrical coils606,607,609and610. Such a circuit, which is an electrical current applying member, may be used in other embodiments.

The driving method of the oscillator device described above may be as follows.

The electrical current signal described above is comprised of a first driving current signal of a periodic signal having a first period (e.g., 20 kHz) and a second driving current signal of a period signal having a second period (e.g., 60 Hz). Then, the amount of electrical current changes of the first to fourth electrical coils by the first driving current signal is the same, and this is referred to as a “current change amount1”. The amount of electrical current changes of the first to fourth electrical coils by the second driving current signal is the same, and this is referred to as “current change amount2”. Based on this assumption, electrical currents are applied to the first to fourth coils, while the electrical current change amount of the first and second electrical coils is taken as the addition of the current change amount1and the current change amount2, and the electrical change amount of the third and fourth electrical coils is taken as the subtraction of the current change amount1and the current change amount2.

In the optical deflector of the present embodiment, the permanent magnet is placed only at the surface opposed to the electrical coil, and thus, a reduction in size is easy. Furthermore, the torsional rotary force can be produced independently of the dual rotational axes, and the orientation of the torsional rotation force coincides with the direction of torsion of the rotary axis. Thus, there is no loss of the torsional rotating force. Furthermore, in this embodiment as well, two-dimensional angular displacement of the movable mirror is accomplished only by applying an electrical current signal to the coil provided on the gimbals. Therefore, it is not necessary to provide a driving member, such as an electrical coil on the movable mirror, and thus, good surface flatness of the movable mirror is assured.

A fourth embodiment of the present invention will be explained.

The present embodiment is an example of an optical deflector having a gimbals structure shown inFIG. 16A-FIG.16C.FIG. 16Ais a top plan view illustrating the structure of an optical deflector of the present embodiment, andFIG. 16Bis a bottom view wherein some structural components are not shown.FIG. 16Cis a sectional view of the optical deflector ofFIG. 16A, taken along a line C-C′.FIG. 17is a top plan view showing an example of permanent magnet disposition, wherein some structural components are not shown.

In this embodiment, as shown inFIG. 16A-FIG.16C, of the four corners of the gimbals601, the electrical coil606and the electrical coil607are placed in a pair of zones, which are in a diagonal positional relationship with each other. On the other hand, the electrical coil609and the electrical coil610are placed in another pair of zones, which are in a diagonal positional relationship with each other. The electrical coil609and the electrical coil610, as well, have windings being wound in the same direction. Thus, the permanent magnet disposed opposed to the electrical coil606and the permanent magnet disposed opposed to the electrical coil607are disposed so that they have opposite magnetic pole directions. Also, the permanent magnet disposed opposed to the electrical coil609and the permanent magnet disposed opposed to the electrical coil601are disposed so that they have opposite magnetic pole directions.

In the case wherein the coils have the same winding direction, only one permanent magnet may be used and, as an example, it may be disposed such as shown inFIG. 17. The remaining features are similar to those in the third embodiment.

A fifth embodiment of the present invention will be explained.

In this embodiment, an optical deflector having a gimbals structure shown inFIG. 18andFIG. 19was designed and manufactured. The present embodiment has a feature that thin film structures1101and1102are added to the structure having been explained with reference to the first embodiment.FIG. 18is a top plan view showing the structure of the optical deflector of the present embodiment.FIG. 19is a sectional view of the optical deflector ofFIG. 18, taken along a line A-A′.FIG. 20is a diagram for explaining advantageous results of the thin film structure. In these figures, reference numerals are not assigned to components other than the coil and the thin film structure.

The structure, except for the thin film structures1101and1102, is the same as that of the first embodiment, and a similar function and advantageous results are provided using a current signal and a driving method explained with reference to the first embodiment.

In this embodiment, the film structures1101and1102and the electrical coils1103and1104are made of the same material, and they have approximately the same shapes. Thus, residual stress and thermal expansion deformation produced with respect to the gimbals at the time of formation are the same. More specifically, in order to provide sufficient advantageous results to be described below, the film structures1101and1102are made of the same material as that of the electrical coils1103and1104, and they have a shape of a coil. The gimbals can be made from monocrystal silicon having good thermal conduction performance. Thus, when heat is generated by applying an electrical current to the electrical coils1103and1104, the electrical coils, gimbals and film structures will have approximately the same temperature. Furthermore, the electrical coils1103and1104are formed on the top surface of the gimbals, whereas the film structures1101and1102are formed on the bottom surface of the gimbals. Furthermore, the electrical coils1103and1104and the film structures1101and1102are localized at diagonal positions in zones quartered by the extension lines of the first and second torsion bars.

In the disposition example of the electrical coils and film structures described above, the following advantageous results will be provided.

(1) The flexure due to the residual stress produced at the time of formation between the coil and gimbals, and the flexure due to the residual stress produced at the time of the formation between the thin-film structure and the gimbals, will cancel each other in the mirror and the first and second torsion bars. Hence, no flexure will be produced.

(2) The thermal expansion deformation produced between the gimbals and the coil due to the heat generated by applying an electrical current to the coil, and the thermal expansion deformation produced between the thin-film structure and the gimbals will cancel each other, and no flexure will be produced.

With this arrangement, the position of the rotational axis based on the first and second torsion bars do not change, and good surface flatness of the mirror is maintained. This is shown inFIG. 20A.

By advantageous results (1) and (2), angular displacement of the mirror in a desired manner about the rotational axis of the first and second torsion bars is enabled, and a two-dimensional scan of the light beam by the movable mirror can be done very precisely. As compared therewith, if the film structures1101and1102are not provided, because of the residual stress and thermal expansion deformation the mirror and the first and second torsion bars will produce flexure, as shown inFIG. 22B.

A sixth embodiment of the present invention is an example of an image display unit, which is a visual display unit, using an optical deflector of the present invention.FIG. 21shows the structure of the present embodiment. In the image display unit of the present embodiment, a direct modulation light source1003is modulated on the basis of a modulating signal1002outputted form a light source modulation driving member1001. Here, the direct modulation light source1003is comprised of a red-color semiconductor laser. The direct modulation light source1003may use a light source configured to directly modulate red, blue and green colors, which may be mixed by using a color mixture optical system. The output light1004directly modulated by the direct modulation light source1003is projected on the reflection surface of an optical deflector1005. The reflected light being deflected by optical deflector1005goes through a correction optical system1006, and it is displayed as an image on an image display1007. The correction optical system1006is an optical system for correcting distortion of an image due to the resonance scan.

The optical deflector1005is an optical deflector according to any one of the preceding embodiments. Based on raster scanning of the output light1004using the optical deflector1005, an image can be displayed on the image display1007, which is the surface to be irradiated with light.

As described above, an image display unit of this embodiment, which has a compact structure, is arranged so that light from a light source is deflected by a compact oscillator device of the present invention, and at least a portion of the light is incident on the surface to be irradiated. Furthermore, an image display unit, which can be driven with a low voltage and which enables a large deflection angle and a high-definition image, is accomplished.