Image projection device

An image projection device includes: a first mirror oscillating to scan an image light beam forming an image projected onto a retina of a user; a light source emitting the image light beam and a detection light beam to the first mirror at different timings; a second mirror having a first region reflecting the image light beam reflected by the first mirror to the retina and a second region reflecting the detection light beam reflected by the first mirror in a direction different from a direction in which the image light beam is reflected, and scanning neither the image light beam nor the detection light beam reflected by the first mirror; a detector detecting the detection light beam reflected by the second region; and a controller adjusting oscillation of the first mirror and an emission timing of the image light beam based on a detection result by the detector.

TECHNICAL FIELD

The present invention relates to an image projection device, and, for example, to an image projection device that directly projects an image onto the retina of a user.

BACKGROUND ART

There have been known image projection devices that project an image by scanning a light beam emitted from a light source in the main scanning direction and the subscanning direction by a scan mirror. In such image projection devices, when the oscillation of the scan mirror and the emission timing of the light beam from the light source deviate from each other, the image quality deteriorates. Thus, a method of correcting the emission timing of the light beam from the light source has been suggested (e.g., see Patent Documents 1 and 2).

There have been also known image projection devices that directly project an image onto the retina of the user. Patent Document 1 directly projects an image onto the retina by scanning a light beam emitted from the light source by a scan mirror and projecting the scanned light onto the retina of the user. In Patent Document 1, the light beam extracted by a half mirror provided in the subsequent stage of the scan mirror is detected by a light detector, and the emission timing of the light beam from the light source is corrected based on the detection result to reduce the deterioration of the image quality.

PATENT DOCUMENT

Patent Document 2: Japanese Patent Application Publication No. 2014-10409

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

The image projection device that directly projects an image onto the retina of the user is preferably small because it is mounted to, for example, the body (face) of the user. However, in Patent Document 1, since the half mirror or the like is provided in the subsequent stage of the scan mirror, the device size increases.

The present invention has been made in view of the above problems, and aims to provide an image projection device that reduces deterioration of image quality and increase in device size.

Means for Solving the Problem

The present invention is an image projection device characterized by including: a first mirror that oscillates in a main scanning direction beyond a range of an image projected onto a retina of a user to scan an image light beam in the main scanning direction, the image light beam forming the image; a light source that emits the image light beam to the first mirror in a period corresponding to the range of the image and emits a detection light beam to the first mirror at time corresponding to an outside of the range of the image in reciprocal oscillation in the main scanning direction of the first mirror; a second mirror that reflects the image light beam reflected by the first mirror to the retina of the user, and reflects the detection light beam reflected by the first mirror in a direction different from a direction in which the image light beam is reflected or transmits the detection light beam; a light detector that detects the detection light beam reflected by the second mirror or the detection light beam passing through the second mirror; and a controller that adjusts oscillation of the first mirror and an emission timing of the image light beam from the light source based on a detection result by the light detector.

In the above configuration, the light source may emit the detection light beam within a period shorter than a period from an end of the range of the image to a turn-round of oscillation in the main scanning direction of the first mirror without making the detection light beam temporally continuous with the image light beam.

In the above configuration, the controller may adjust the oscillation of the first mirror and the emission timing of the image light beam so that a light intensity of the detection light beam detected by the light detector increases.

In the above configuration, the light source may emit the detection light beam in each of a going path and a return path of the reciprocal oscillation of the first mirror without making the detection light beam in the going path and the detection light beam in the return path temporally continuous with each other, and the controller may adjust the oscillation of the first mirror and the emission timing of the image light beam based on a detection result of the detection light beam emitted in the going path and a detection result of the detection light beam emitted in the return path.

In the above configuration, the light source may emit the detection light beam at each side of the range of the image, and the controller may adjust the oscillation of the first mirror and the emission timing of the image light beam based on a detection result of the detection light beam emitted at the each side of the range of the image.

In the above configuration, the second mirror may have a first region that reflects the image light beam and a second region that reflects the detection light beam in a direction different from a direction in which the image light beam is reflected, the light detector may detect the detection light beam reflected by the second mirror, and in the second mirror, the second region may be located next to the first region in a direction corresponding to the main scanning direction, and may protrude or may be recessed with respect to the first region.

In the above configuration, the second region of the second mirror may have a reflecting surface having a dimension not greater than a width of the detection light beam in the direction corresponding to the main scanning direction.

In the above configuration, the light detector may detect the detection light beam passing through the second mirror, and has a light receiving region not larger than a width of the detection light beam.

In the above configuration, the first mirror and the second mirror may be provided to a spectacle type frame, and the light detector may be provided to an external device different from the spectacle type frame.

In the above configuration, the first mirror, the second mirror, and the light detector may be provided to a spectacle type frame.

Effects of the Invention

The present invention can reduce deterioration of image quality and inhibit increase in device size.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Hereinafter, with reference to drawings, embodiments of the present invention will be described.

First Embodiment

FIG. 1illustrates an image projection device100in accordance with a first embodiment as viewed from above. InFIG. 1, a light beam50(including an image light beam52and a detection light beam54) represents the central portion of a light beam having a finite luminous flux diameter. The image projection device100of the first embodiment is a retina-projection type head-mounted display using Maxwellian view in which the image light beam for causing the user to visually recognize an image is directly projected onto a retina72of an eye ball70of the user. The image projection device100of the first embodiment includes a light source12, a first mirror14, a second mirror16, a light detector18, and a controller20as illustrated inFIG. 1. The first mirror14and the second mirror16are located in a spectacle type frame30. The light source12, the light detector18, and the controller20are included in an external device40such as, for example, a mobile terminal.

The light source12emits a light beam50of a single wavelength or a plurality of wavelengths under the instruction of the controller20. The light beam50includes the image light beam52for projecting an image onto the retina72of the user and the detection light beam54for detecting the emission timing of the image light beam52with respect to the oscillation of the first mirror14. That is, the controller20causes the light source12to emit the image light beam52based on input image data, and causes the light source12to emit the detection light beam54for detecting the emission timing of the image light beam52with respect to the oscillation of the first mirror14.

The light source12emits, for example, a red laser light (wavelength: approximately 610 nm to 660 nm), a green laser light (wavelength: approximately 515 nm to 540 nm), and a blue laser light (wavelength: approximately 440 nm to 480 nm). Non-limiting examples of the light source12emitting red, green, and blue laser lights include a light source in which, for example, respective laser diode chips for RGB (red/blue/green), a three-color synthesis device, and a micro collimating lens are integrated.

The first mirror14is located in a temple32of the spectacle type frame30. The light beam50, which is emitted from the light source12and goes through a half mirror60, an optical fiber62, a lens and a mirror, which are not illustrated, and the like, enters the first mirror14. The first mirror14reflects the image light beam52emitted from the light source12, and scans the image light beam52in the main scanning direction and the subscanning direction. The first mirror14both-way scans the image light beam52in the main scanning direction, and one-way scans the image light beam52in the subscanning direction, for example. The main scanning direction and the subscanning direction are directions perpendicular to each other, and the main scanning direction is a horizontal direction, while the subscanning direction is a vertical direction. Additionally, the first mirror14reflects the detection light beam54emitted from the light source12. The first mirror14is, for example, a micro electro mechanical system (MEMS) mirror.

The image light beam52and the detection light beam54reflected by the first mirror14are reflected by a mirror64toward a lens34of the spectacle type frame30. The second mirror16is located on a surface at the eye ball70side of the lens34of the spectacle type frame30. Thus, the image light beam52and the detection light beam54reflected by the mirror64enter the second mirror16. The second mirror16is a half mirror having a free curved surface or a composite structure of a free curved surface and a diffraction surface in a first region16awhere the image light beam52is incident. Thus, the image light beam52entering the second mirror16converges near a pupil74of the eye ball70of the user, and then is projected onto the retina72. This allows the user to visually recognize the image by the image light beam52and visually recognize an external world image through the lens34.

On the other hand, the second mirror16is a half mirror having a shape protruding with respect to the first region16ain a second region16bwhere the detection light beam54is incident. Thus, the detection light beam54entering the second mirror16is reflected in a direction different from the direction in which the image light beam52is reflected. For example, the detection light beam54is reflected by the second mirror16so that the detection light beam54travels back along a light path that is the same as the light path along which the detection light beam54traveled toward the second mirror16. The protruding shape of the second region16bis minute, thus hardly affecting the vision of the user.

The detection light beam54reflected by the second mirror16is reflected by the mirror64and the first mirror14, then goes through the optical fiber62, and is split by the half mirror60. The split detection light beam54enters the light detector18. Accordingly, the light detector18can detect the detection light beam54reflected by the second mirror16. The detection result by the light detector18is output to the controller20. The light detector18is, for example, a photodetector. The light detector18detects the detection light beam54at a time constant, for example, equal to or greater than the period of the reciprocal oscillation in the main scanning direction of the first mirror14.

In the second mirror16, the second region16bis located next to the first region16ain the direction corresponding to the main scanning direction. Additionally, the second region16bis formed so as to have a reflecting surface narrower than the width of the detection light beam54incident to the second region16bin the direction corresponding to the main scanning direction. For example, the second region16bis formed so as to have a reflecting surface having dimensions approximately equal to one pixel or several pixels of the image projected onto the retina72in the direction corresponding to the main scanning direction.

Here, the image light beam52and the detection light beam54will be described in detail.FIG. 2is a diagram for describing emission timings of the image light beam52and the detection light beam54with respect to the oscillation of the first mirror14. InFIG. 2, the oscillation of the first mirror14is indicated by reference numeral80. As illustrated inFIG. 2, the first mirror14oscillates in the main scanning direction and the subscanning direction beyond an image range82projected onto the retina72. The light source12emits the image light beam52for a period during which the oscillation of the first mirror14is in the image range82in both the going path and the return path of the reciprocal oscillation in the main scanning direction of the first mirror14. This configuration causes the image light beam52to be scanned by the first mirror14. The reason why the image light beam52is scanned in the range within which the oscillation angle of the first mirror14is small is because the distortion of the projected image is large if the image is projected onto the retina72by scanning the image light beam52in the range within which the oscillation angle of the first mirror14is large. The image light beam52may not be necessarily scanned in a rectangular shape, and may be scanned in other shapes such as a trapezoidal shape.

In the reciprocal oscillation in the main scanning direction of the first mirror14, at the time (timing) when the oscillation of the first mirror14is outside the image range82, the light source12emits the detection light beam54having a predetermined light intensity. The detection light beam54is emitted from the light source12in each of the going path and the return path of the reciprocal oscillation of the first mirror14. The detection light beam54may be a light beam of a single wavelength. It is only required that the detection light beam54has a light intensity enough to be detected by the light detector18, and the light intensity may be constant.

FIG. 3is a timing chart illustrating emission timings of the image light beam52and the detection light beam54with respect to the oscillation of the first mirror14. As illustrated inFIG. 3, the timing when the emission of the image light beam52to be scanned first in the image range82(here, an image light beam52ain the going path of the reciprocal oscillation of the first mirror14) is started is determined by using the oscillation angle in the main scanning direction of the first mirror14as a reference. The oscillation angle in the main scanning direction of the first mirror14can be detected by a sensor not illustrated.

After the emission of the image light beam52a, of which the emission has been started at the timing determined by using the oscillation angle of the first mirror14as a reference, ends, an image light beam52bin the return path of the reciprocal oscillation of the first mirror14and the image light beam52ain the going path are repeatedly emitted. These image light beams52aand52bare repeatedly emitted based on an elapsed time from the start of the emission of the image light beam52aof which the emission has been started with reference to the oscillation angle of the first mirror14. That is, after a predetermined time T1elapses from the start of the emission of the image light beam52aof which the emission has started with reference to the oscillation angle of the first mirror14, the emission of the image light beam52bin the return path is started, and after another predetermined time T1passes, the emission of the image light beam52ain the going path is started. The operations described above are repeated until the image of one frame is formed. For example, an interval 2T1at which the image light beam52ain the going path is emitted is approximately 35 μsec.

A detection light beam54ain the going path of the reciprocal oscillation of the first mirror14and a detection light beam54bin the return path are emitted from the light source12singly between the emissions of the image light beams52aand52b. The detection light beam54ain the going path is emitted singly after a predetermined time T2elapses from the start of the emission of the image light beam52aof which the emission has been started with reference to the oscillation angle of the first mirror14. The detection light beam54bin the return path is emitted singly after a predetermined time T3elapses from the start of the emission of the image light beam52aof which the emission has started with reference to the oscillation angle of the first mirror14. That is, the light source12emits each of the detection light beams54aand54bwithin the period shorter than the period from the end of the image range82to the turn-round of the oscillation in the main scanning direction of the first mirror14without making the detection light beams54aand54btemporally continuous with the image light beams52aand52b. The light source12emits the detection light beam54ain the going path and the detection light beam54bin the return path without making them temporally continuous with each other. A time interval T4between the image light beam52aand the detection light beam54ais set equal to a time interval T5between the image light beam52band the detection light beam54b. Thus, the detection light beams54are set so that the detection light beams54are positioned in the same line in the subscanning direction as illustrated inFIG. 2. The time intervals T4and T5are, for example, approximately 1 μsec.

As described above, the emission of the image light beam52is started based on the oscillation angle of the first mirror14, and the image light beam52and the detection light beam54thereafter are emitted from the light source12at the predetermined constant timings.

Here, when there is no shift in relative projection position between the image light beam52ain the going path and the image light beam52bin the return path in the reciprocation scanning in the main scanning direction, an image with good image quality is projected onto the retina72as illustrated inFIG. 4A. However, physical properties of the light source12and the first mirror14, an electric circuit, or the like may change depending on temperature and the lapse of time. In this case, a shift in relative projection position between the image light beam52ain the going path and the image light beam52bin the return path occurs, and thereby the image projected onto the retina72may be seen double as illustrated inFIG. 4B.

To inhibit such deterioration of image quality, in the first embodiment, the detection light beam54reflected by the second mirror16is detected by the light detector18, and the controller20adjusts the emission timing of the image light beam52based on the detection result by the light detector18. A processor such as a central processing unit (CPU) and memories such as a random access memory (RAM) and a read only memory (ROM) function as the controller20. The processor functions as the controller20according to the program stored in the memory.

FIG. 5andFIG. 6are flowcharts of exemplary processes by the controller20of the image projection device100of the first embodiment. As illustrated inFIG. 5, at step S10, the controller20causes the light source12to start the emission of the image light beam52ain the going path based on the oscillation angle in the main scanning direction of the first mirror14. Then, at step S12, the controller20ends the emission of the image light beam52aafter a predetermined emission time elapses.

Then, at step S14, the controller20causes the light source12to emit the detection light beam54ain the going path after a predetermined time (T2) elapses from the emission start timing at which the emission of the image light beam52ahas been started based on the oscillation angle of the first mirror14. Then, at step S16, the controller20causes the light source12to emit the detection light beam54bin the return path after a predetermined time (T3) elapses from the emission start timing at which the emission of the image light beam52ahas been started based on the oscillation angle of the first mirror14.

Then, at step S18, the controller20causes the light source12to start the emission of the image light beam52bin the return path after a predetermined time (T1) elapses from the emission start timing at which the emission of the image light beam52ahas been started based on the oscillation angle of the first mirror14. Then, at step S20, the controller20ends the emission of the image light beam52bafter a predetermined emission time elapses.

Then, at step S22inFIG. 6, the controller20obtains the detection results of the detection light beams54aand54breflected by the second mirror16by the light detector18. For example, the controller20obtains the light intensities of the detection light beams54aand54bdetected by the light detector18for a predetermined period (for example, the period equal to or greater than the period of the reciprocal oscillation in the main scanning direction of the first mirror). In this case, the controller20can start the detection by the light detector18before step S10inFIG. 5and end the detection by the light detector18after step S20. The controller20can obtain the sum of the values of integral of the light intensities of the detection light beams54aand54bin the predetermined period by obtaining the light intensities of the detection light beams54aand54bdetected by the light detector18for the predetermined period. The controller20stores the obtained sum of the values of integral of the light intensities in a storage unit not illustrated.

Then, at step S24, the controller20determines whether a deviation beyond an allowable range occurs between the oscillation in the main scanning direction of the first mirror14and the emission timings of the image light beams52aand52bbased on the detection results of the detection light beams54aand54bby the light detector18.

Here, the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bwill be described withFIG. 7AandFIG. 7B.FIG. 7AandFIG. 7Bare diagrams for describing the detection of the detection light beams54aand54bby the light detector18. In each ofFIG. 7AandFIG. 7B, the horizontal axis represents the position in the second mirror16in the direction corresponding to the main scanning direction, and the vertical axis represents the light intensities of the detection light beams54aand54b.FIG. 7Aillustrates a case where the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bis small, andFIG. 7Billustrate a case where the deviation is large.

As described inFIG. 1, the second region16bof the second mirror16is formed so as to have a reflecting surface having a width narrower than the width of the detection light beam54in the direction corresponding to the main scanning direction. Accordingly, the range of the detection light beam54reflected by the second region16bof the second mirror16is limited, and as illustrated inFIG. 7AandFIG. 7B, the range of the detection light beam54that can be detected by the light detector18(a detectable range18a) is narrow in the direction corresponding to the main scanning direction. In this case, when the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bis small, since the detection light beams54are set so as to be positioned on the same line in the subscanning direction as illustrated inFIG. 2, the light intensities of the detection light beams54aand54bin the detectable range18aare relatively large as illustrated inFIG. 7A. Thus, the sum of the values of integral of the light intensities of the detection light beams54aand54bdetected by the light detector18for the predetermined period is relatively large. In this case, as illustrated inFIG. 4A, an image with good image quality is projected onto the retina72.

On the other hand, when the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bis large, since the detection light beams54are not positioned on the same line in the subscanning direction, the light intensities of the detection light beams54aand54bin the detectable range18aare relatively small as illustrated inFIG. 7B. Thus, the sum of the values of integral of the light intensities of the detection light beams54aand54bdetected by the light detector18for the predetermined period is relatively small. In this case, the quality of an image projected onto the retina72deteriorates as illustrated inFIG. 4B.

The above fact reveals that it can be determined that the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bis within the allowable range when the sum of the values of integral of the light intensities of the detection light beams54aand54bdetected by the light detector18for the predetermined period is equal to or greater than a predetermined value. The predetermined value is a threshold value that divides the image quality of an image projected onto the retina72into good or bad, and is preliminarily stored in a storage unit not illustrated. For example, as the predetermined value, the maximum value of the sum of the values of integral of the light intensities of the detection light beams54aand54bpossibly detected by the light detector18for the predetermined period, a value between values less than the maximum value by approximately 5%, or a value between values less than the maximum value by approximately 10% may be used.

Referring back toFIG. 6, when the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bexceeds the allowable range (step S24: No), the process moves to step S26, and the controller20conducts adjustment between the oscillation of the first mirror14and the emission timings of the image light beams52aand52b.

Here, with reference toFIG. 8, the adjustment between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bwill be described.FIG. 8is a timing chart illustrating emission timings of the image light beams52aand52band the detection light beams54aand54bwith respect to the oscillation of the first mirror14before and after the adjustment. InFIG. 8, the emission timings before the adjustment are indicated by dashed lines, and the emission timings after the adjustment are indicated by solid lines.

As illustrated inFIG. 8, the controller20shifts the emission timings of all the image light beams52aand52band the detection light beams54aand54bwith respect to the oscillation in the main scanning direction of the first mirror14so that the sum of the values of integral of the light intensities of the detection light beams54aand54bin the predetermined period is not less than the predetermined value. For example, the controller20shifts the emission timings of all the image light beams52aand52band the detection light beams54aand54bin increments of one pixel. The controller20also stores the shift amount of the emission timings of all the image light beams52aand52band the detection light beams54aand54bin a storage unit not illustrated. A table that relates the difference between the sum of the values of integral of the light intensities of the detection light beams54aand54band the predetermined value to the shift amount of the emission timings may be preliminarily stored in a storage unit not illustrated, and the controller20may determine the shift amount of the emission timings using this table.

After conducting the adjustment between the oscillation of the first mirror14and the emission timings of the image light beams52aand52b, the controller20moves to step S28. When the deviation between the oscillation of the first mirror14and the emission timings of the image light beams52aand52bis within the allowable range at step S24, the controller20also moves to step S28.

At step S28, the controller20repeatedly emits the image light beam52ain the going path and the image light beam52bin the return path until the projection of an image of one frame ends.

After the projection of the image of one frame is ended, when there is a next frame (step S30: Yes), the process returns to step S10inFIG. 5, and the controller20starts the emission of the image light beam52ain the next frame based on the oscillation angle of the first mirror14and the shift amount of the emission timing stored in the storage unit. Thereafter, step S12through step S28are executed. On the other hand, when there is no next frame (step S30: No), the processes ofFIG. 5andFIG. 6are ended.

The controller20shifts the emission timings of all the image light beams52aand52band the detection light beams54aand54bin the direction opposite to that of the previous time at step S26when the sum of the values of integral of the light intensities of the detection light beams54aand54bobtained at step S24for the next frame is less than the sum of the values of integral stored in the storage unit.

FIG. 9Ais a diagram for describing emission timings of the image light beam52and the detection light beam54with respect to the oscillation of the first mirror14before the adjustment, andFIG. 9Bis a diagram for describing emission timings of the image light beam52and the detection light beam54with respect to the oscillation of the first mirror14after the adjustment. Repetitive execution of the controls ofFIG. 5andFIG. 6reduces the deviation of the emission timing of the image light beam52with respect to the oscillation of the first mirror14as illustrated inFIG. 9Beven when the emission timing of the image light beam52with respect to the oscillation of the first mirror14deviates as illustrated inFIG. 9A. Accordingly, an image with good image quality illustrated inFIG. 4Acan be projected.

As described above, in the first embodiment, in the reciprocal oscillation in the main scanning direction of the first mirror14, the detection light beam54enters the first mirror14at time corresponding to the outside of the image range82. The controller20adjusts the first mirror14and the emission timing of the image light beam52based on the detection result of the detection light beam54by the light detector18. This configuration reduces the deviation between the oscillation of the first mirror14and the emission timing of the image light beam52as described inFIG. 8throughFIG. 9B, and thus, the deterioration in quality of the image projected onto the retina72is reduced. Additionally, the second mirror16includes the second region16bthat reflects the detection light beam54in the direction different from the direction in which the image light beam52is reflected in addition to the first region16athat reflects the image light beam52to the retina72, and the detection light beam54reflected by the second region16bis detected by the light detector18. This configuration inhibits the increase in the number of components, thereby inhibiting the increase in device size.

Moreover, in the first embodiment, the second region16bof the second mirror16is located next to the first region16ain the direction corresponding to the main scanning direction, and has a protruding shape with respect to the first region16a. Accordingly, the second mirror16can reflect the detection light beam54toward the side at which the first mirror14and the like are located. Thus, the light detector18detecting the detection light beam54can be arranged together with other components. For example, by configuring the second mirror16to reflect the detection light beam54so that the detection light beam54travels back along the light path identical to the light path along which the detection light beam54traveled, the light detector18can be provided to the external device40. The first embodiment describes a case where the second region16bof the second mirror16protrudes with respect to the first region16aas an example, but the second region16bmay be recessed with respect to the first region16aas in an image projection device150in accordance with a first variation of the first embodiment illustrated inFIG. 10.

In the first embodiment, the detection light beam54is emitted within the period shorter than the period from the end of the image range82to the turn-round of the oscillation in the main scanning direction of the first mirror14without being temporally continuous with the image light beam52. The second region16bof the second mirror16has a reflecting surface narrower than the width of the detection light beam54in the direction corresponding to the main scanning direction. This configuration easily enables to detect the detection light beam54reflected by the second region16bof the second mirror16by the light detector18and adjust the oscillation of the first mirror14and the emission timing of the image light beam52based on the detection result. The first embodiment describes a case where the second region16bof the second mirror16has a reflecting surface narrower than the width of the detection light beam54in the direction corresponding to the main scanning direction as an example, but does not intend to suggest any limitation, and the second region16bof the second mirror16may have a reflecting surface not larger than the width of the detection light beam54.

In the first embodiment, in each of the going path and the return path of the reciprocal oscillation in the main scanning direction of the first mirror14, the detection light beams54aand54bare emitted so that the detection light beam54ain the going path is temporally discontinuous with the detection light beam54bin the return path. The controller20adjusts the oscillation of the first mirror14and the emission timing of the image light beam52based on the detection result of the detection light beam54aemitted in the going path and the detection result of the detection light beam54bemitted in the return path. By using the detection light beams54aand54brespectively emitted in the going path and the return path, the oscillation of the first mirror14and the emission timing of the image light beam52are more precisely adjusted.

In the first embodiment, the first mirror14and the second mirror16are located in the spectacle type frame30, and the light detector18is included in the external device40. This configuration reduces the number of components equipped to the spectacle type frame30, thereby inhibiting increase in size.

The first embodiment describes a case where the oscillation of the first mirror14and the emission timing of the image light beam52are adjusted by correcting the emission timing of the image light beam52so that the light intensity of the detection light beam54detected by the light detector18increases, but does not intend to suggest any limitation. For example, the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted based on the time at which the detection light beam54was detected by the light detector18. For example, a freely-selected point in the oscillation angle in the main scanning direction of the first mirror14is defined as an original time. When the oscillation of the first mirror14and the emission timing of the image light beam52do not deviate from each other, the time from the original time to the time at which the light detector18detects the detection light beam54is preliminarily stored as the criterion time interval in a storage unit not illustrated. Then, the time interval from the original time to the time at which the light detector18actually detected the detection light beam54is compared with the criterion time interval, and the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted by correcting the emission timing of the image light beam52so that the difference therebetween decreases. When the oscillation of the first mirror14and the emission timing of the image light beam52are adjusted based on the magnitude of the light intensity of the detection light beam54, the adjustment may be conducted based on the sum of the values of integral of the light intensity of the detection light beam54in the predetermined period or based on, for example, the maximum value of the light intensity of the detection light beam54.

In the first embodiment, the detection light beam54may enter the first mirror14in only one of the going path and the return path of the reciprocal oscillation in the main scanning direction of the first mirror14, and the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted based on the detection result of this detection light beam54.

In the first embodiment, a plurality of pairs of the detection light beams54aand54b, where the detection light beams54aand54bform one pair, may enter the first mirror14, and the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted based on the detection results of the plurality of pairs of the detection light beams54aand54b. In this case, the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted based on the average of the detection results of the plurality of pairs of the detection light beams54aand54b.

The first embodiment describes a case where the oscillation of the first mirror14and the emission timing of the image light beam52are adjusted in the process of projecting an image of one frame as described at steps S24and S26inFIG. 6as an example, but the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted after the projection of the image of one frame ends. Alternatively, the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted every time when an image of one frame is projected, or the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted once per projections of images of multiple frames.

Second Embodiment

FIG. 11illustrates an image projection device200in accordance with a second embodiment as viewed from above. In the image projection device200of the second embodiment, as illustrated inFIG. 11, in the second mirror16, the second regions16bare located at both sides of the first region16ain the direction corresponding to the main scanning direction. The detection light beam54emitted from the light source12enter both the two second regions16b. Other structures are the same as or similar to those of the first embodiment, and the description thereof is thus omitted.

FIG. 12is a diagram for describing emission timings of the image light beam52and the detection light beam54with respect to the oscillation of the first mirror14. As illustrated inFIG. 12, in the reciprocal oscillation in the main scanning direction of the first mirror14, the detection light beam54is emitted from the light source12at the time (timing) when the oscillation of the first mirror14is at each side of the image range82. Other structures are the same as or similar to those of the first embodiment, and the description thereof is thus omitted.

The controller20of the image projection device200of the second embodiment adjusts the oscillation of the first mirror14and the emission timing of the image light beam52based on the detection result of the detection light beam54emitted at each side of the image range82. The adjustment method is the same as or similar to the method described in the first embodiment, and the description thereof is thus omitted.

In the second embodiment, the detection light beam54is emitted from the light source12to the first mirror14at each side of the image range82. The controller20adjusts the oscillation of the first mirror14and the emission timing of the image light beam52based on the detection result of the detection light beam54emitted at each side of the image range82. As described above, use of the detection light beam54emitted at each side of the image range82enables to more precisely adjust the oscillation of the first mirror14and the emission timing of the image light beam52.

In the second embodiment, the oscillation of the first mirror14and the emission timing of the image light beam52may be adjusted based on the average of the detection result of the detection light beam54emitted at one side of the image range82and the detection result of the detection light beam54emitted at the other side of the image range82.

Third Embodiment

FIG. 13illustrates an image projection device300in accordance with a third embodiment as viewed from above. In the image projection device300of the third embodiment, as illustrated inFIG. 13, the light source12and the light detector18are located in the temple32of the spectacle type frame30. The detection light beam54is reflected by the second region16bof the second mirror16toward the light detector18located in the temple32of the spectacle type frame30. Other structures are the same as or similar to those of the first embodiment, and the description thereof is thus omitted.

In the third embodiment, the first mirror14, the second mirror16, and the light detector18are located in the spectacle type frame30. This configuration enables to easily achieve the structure in which the detection light beam54reflected by the second mirror16is detected by the light detector18.

In the third embodiment, as in the first embodiment and the second embodiment, the light source12may be included in the external device40. In the first embodiment and the second embodiment, as in the third embodiment, the light source12may be located in the temple32of the spectacle type frame30.

In the first through third embodiments, when the detection light beam54entering the second region16bof the second mirror16is a diffusion light, the second region16bmay be structured to have a reflecting surface with a protruding shape. This configuration allows the detection light beam54to be collected to the optical fiber62in the first embodiment and the second embodiment, and allows the detection light beam54to be collected to the light detector18in the third embodiment.

Fourth Embodiment

FIG. 14illustrates an image projection device400in accordance with a fourth embodiment as viewed from above. In the image projection device400of the fourth embodiment, as illustrated inFIG. 14, the light source12is located in the temple32of the spectacle type frame30. The light detector18is located on the opposite surface of the lens34of the spectacle type frame30from the eye ball70. In the second mirror16, the second region16bwhere the detection light beam54is incident has a shape that is flat with respect to the first region16a, where the image light beam52is incident, and optically discontinuous with the first region16a. This structure inhibits the detection light beam54from being projected onto the retina72of the eye ball70together with the image light beam52. Since the second mirror16is a half mirror, a part of the detection light beam54passes through the second mirror16. The light detector18detects the detection light beam54passing through the second mirror16. The dimensions of the light receiving region of the light detector18are not greater than the width of the detection light beam54. Other structures are the same as or similar to those of the first embodiment, and the description thereof is thus omitted.

As described in the fourth embodiment, the light detector18may be located on the opposite surface of the lens34of the spectacle type frame30from the eye ball70. Since the second mirror16is a half mirror, the light detector18can detect the detection light beam54passing through the second mirror16. Since the light detector18has a light receiving region not larger than the width of the detection light beam54, the oscillation of the first mirror14and the emission timing of the image light beam52can be easily adjusted.

In the fourth embodiment, as in the first embodiment and the second embodiment, the light source12may be included in the external device40.

The first through fourth embodiments describe reciprocation scanning in which the image light beam52is scanned in the going path and the return path of the reciprocal oscillation in the main scanning direction of the first mirror14as an example, but one-way scanning in which the image light beam52is scanned in only one of the going path and the return path may be employed. The first through fourth embodiments use as an example of the light beam50emitted from the light source12a laser light having an efficiency advantage, but the light beam50is not limited to the laser light. The second mirror16is not limited to a mirror that splits the intensity of the reflected light and the transmitted light to 1:1.

Although the desirable embodiments of the present invention has been described in detail, the present invention is not limited to a certain embodiment, and it should be understood that the various change, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.