Patent Description:
In recent years, augmented reality (AR) glasses that display a virtual image, various information, and the like in a superimposed manner on an actual view have been in practical use. The AR glasses are also referred to as smart glasses, a head mounted display (HMD), AR eyeglasses, and the like.

Some AR glasses employ a method of directly scanning laser light emitted from a light source to retinas of eyes of a user by directionally changing the laser light using a movable mirror (also referred to as a micro electro mechanical systems (MEMS) mirror) configured with MEMS. This method is referred to as a retinal scanning method. In the AR glasses of the retinal scanning method, the laser light directionally changed by the movable mirror is condensed to pupils of the eyes of the user by a condensing optical system and is scanned to the retinas. Since the retinal scanning method does not depend on a focus adjustment function of crystalline lenses of the eyes, the user can clearly see a video projected to the retinas even in a case where the user is nearsighted or farsighted or has presbyopia. In addition, the AR glasses of the retinal scanning method have high energy efficiency and thus, can be driven for a long time period.

On the other hand, the AR glasses of the retinal scanning method have a problem in that the video is not seen in a case where a condensing point of the laser light by the condensing optical system does not match positions of the pupils. That is, the video is not seen in a case where the positions of the pupils deviate from the condensing point because the user moves the eyes. This problem is known as a narrow movable range of the eyes for clearly seeing the video, that is, a narrow eyebox.

Accordingly, an objective for the AR glasses of the retinal scanning method is to expand the eyebox. <CIT> discloses a technology for expanding an eyebox by replicating laser light directionally changed by a movable mirror using a prism or a light guide plate. In addition, <NPL> discloses a technology for expanding an eyebox by condensing laser light to positions of pupils using a mirror while tracking the positions of the pupils using eye tracking.

<CIT> discloses a compact, HUD eyeglass display system that makes it possible to superimpose a wide-angle computer-generated view on the real-world view. Without obscuring the wearer's vision or requiring any additional optical element such as beam splitters or contact lenses.

<CIT> discloses an augmented reality headset that may include a reflective holographic combiner to direct light from a light engine into a user's eye while also transmitting light from the environment.

<CIT> discloses an object displaying system including a right light signal generator, a left light signal generator, a right combiner, and a left combiner.

<CIT> discloses a direct retinal projector that may include a gaze tracking system that tracks position of a subject's pupil and automatically adjusts projection of a scanned light field so that the light field enters the pupil.

<CIT> discloses a near-to-eye display system for forming an image as an illuminated region on a retina of at least one eye of a user. The system includes a source of modulated light, a proximal optic positionable adjacent an eye of the user to receive the modulated light.

However, the technologies disclosed in <CIT> and <NPL> have a complicated configuration for expanding the eyebox. Thus, a technology that can expand the eyebox with a simpler configuration is desired.

An object of the disclosed technology is to provide a light scanning device that can expand an eyebox with a simple configuration.

In order to accomplish the above object, a light scanning device according to an aspect of the present disclosure comprises a light source that emits laser light, a mirror device that includes a movable mirror swinging about at least one axis and directionally changes the laser light emitted from the light source by reflecting the laser light using the movable mirror, and a condensing optical system that condenses the laser light directionally changed by the mirror device to a center of an eyeball.

The condensing optical system is a half-silvered mirror or a mirror having a concave surface and condenses at least a part of the laser light directionally changed by the mirror device to the center of the eyeball by reflecting at least the part of the laser light using the concave surface.

The concave surface is an elliptical surface, and a swinging axis of the movable mirror is positioned at one focal point of the elliptical surface, and the center of the eyeball is positioned at the other focal point of the elliptical surface.

In an illustrative example not according to the invention, the condensing optical system is composed of a grating or a hologram.

It is preferable that the movable mirror is configured to be swingable about a first axis and a second axis that are orthogonal to each other.

According to the disclosed technology, a light scanning device that can expand an eyebox with a simple configuration can be provided.

Hereinafter, an embodiment according to the disclosed technology will be described in detail with reference to the drawings. As an example, a form of applying a light scanning device according to the embodiment of the disclosed technology to AR glasses will be described in each embodiment below.

<FIG> illustrates a configuration of AR glasses <NUM> according to the present embodiment. As illustrated in <FIG>, the AR glasses <NUM> are configured with a frame <NUM>, two lenses <NUM>, two temples <NUM>, a module <NUM>, and a half-silvered mirror <NUM>. The two lenses <NUM> are held in the frame <NUM>. Each of the two temples <NUM> is connected to an end part of the frame <NUM> through a hinge (not illustrated).

The module <NUM> is provided in one of the two temples <NUM>. In addition, the half-silvered mirror <NUM> is provided in the lens <NUM> on a temple <NUM> side in which the module <NUM> is provided out of the two lenses <NUM>. In the present embodiment, the module <NUM> is provided in the temple <NUM> on a right eye side, and the half-silvered mirror <NUM> is provided in the lens <NUM> on the right eye side. The module <NUM> may be provided in both of the two temples <NUM>, and the half-silvered mirror <NUM> may be provided in both of the lenses <NUM>.

The module <NUM> emits laser light L modulated in accordance with an image signal toward the half-silvered mirror <NUM>. The half-silvered mirror <NUM> reflects the laser light L and condenses the laser light L to a center of an eyeball of a user wearing the AR glasses <NUM>. Reference numeral P denotes a condensing position of the laser light L by the half-silvered mirror <NUM>. The half-silvered mirror <NUM> is an example of a "condensing optical system" according to the embodiment of the disclosed technology.

<FIG> illustrates configurations of the module <NUM> and the half-silvered mirror <NUM>. As illustrated in <FIG>, the module <NUM> comprises a control device <NUM>, a micro electro mechanical systems (MEMS) driver <NUM>, a light emitting device <NUM>, a multiplexing optical system <NUM>, a collimator <NUM>, and a MEMS mirror <NUM>. The MEMS mirror <NUM> is an example of a "mirror device" according to the embodiment of the disclosed technology.

The light emitting device <NUM> includes a laser driver <NUM> and a laser light source <NUM>. The laser driver <NUM> of the present embodiment drives the laser light source <NUM> based on an intensity modulation signal supplied from the control device <NUM> and causes the laser light L for forming an image to be output from the laser light source <NUM>. For example, the laser light source <NUM> outputs the laser light L of three colors of red (R), green (G), and blue (B). The laser light source <NUM> is an example of "light source" according to the embodiment of the disclosed technology.

The laser light L output from the laser light source <NUM> is multiplexed by the multiplexing optical system <NUM>. Then, the MEMS mirror <NUM> is irradiated with the multiplexed laser light L through the collimator <NUM>. The laser light L with which the MEMS mirror <NUM> is irradiated is reflected toward the half-silvered mirror <NUM> by the MEMS mirror <NUM>.

The MEMS driver <NUM> drives the MEMS mirror <NUM> under control of the control device <NUM>. In the MEMS mirror <NUM>, a mirror portion <NUM> (refer to <FIG>) that reflects the laser light independently swings about each of two axes orthogonal to each other as a central axis. In the present embodiment, the laser light is scanned in a state of drawing a Lissajous curve on the half-silvered mirror <NUM> by the swing of the mirror portion <NUM> based on a driving signal. The Lissajous curve is a curve that is decided by a swing frequency about a first axis, a swing frequency about a second axis, and a phase difference therebetween. The mirror portion <NUM> is an example of a "movable mirror" according to the embodiment of the disclosed technology. The MEMS mirror <NUM> directionally changes the laser light L by reflecting the laser light L using the mirror portion <NUM>. Directional changing refers to changing a traveling direction of the laser light L.

The control device <NUM> of the present embodiment includes a field programmable gate array (FPGA) 20A and a memory 20B. For example, the memory 20B is a volatile memory and stores various information such as the image signal representing the image projected to the half-silvered mirror <NUM>. For example, the memory 20B stores the image signal input from an outside of the AR glasses <NUM>.

A concave surface 15A that specularly reflects at least a part of the laser light L incident from the MEMS mirror <NUM> is formed in the half-silvered mirror <NUM>. In addition to specularly reflecting at least a part of the laser light L, the half-silvered mirror <NUM> transmits external light. In the present embodiment, the concave surface 15A is an elliptical surface. More specifically, the concave surface 15A is a surface of a part of a rotational ellipsoid obtained by rotating an ellipse about an axis passing through two focal points of the ellipse. That is, the concave surface 15A is an off-axis elliptical surface. Light output from one focal point always reaches the other focal point in a case where the light is specularly reflected by the concave surface 15A.

The AR glasses <NUM> are configured such that a swinging axis of the MEMS mirror <NUM> is positioned at one focal point of the concave surface 15A and a center of an eyeball EB of the user is positioned at the other focal point. Based on this geometrical relationship, the laser light L incident on the half-silvered mirror <NUM> from the MEMS mirror <NUM> is reflected by the concave surface 15A and is condensed to the center of the eyeball EB.

<FIG> illustrates an example of a configuration of the MEMS mirror <NUM>. The MEMS mirror <NUM> includes the mirror portion <NUM>, a first support portion <NUM>, a first movable frame <NUM>, a second support portion <NUM>, a second movable frame <NUM>, a connecting portion <NUM>, and a fixed frame <NUM>.

The mirror portion <NUM> has a reflecting surface 40A on which an incidence ray is reflected. For example, the reflecting surface 40A is formed with a thin metal film of gold (Au), aluminum (Al), silver (Ag), or a silver alloy. For example, a shape of the reflecting surface 40A is a circular shape.

The first support portion <NUM> is arranged outside the mirror portion <NUM> at each of positions that face with a second axis a<NUM> interposed therebetween. The first support portions <NUM> are connected to the mirror portion <NUM> on a first axis a<NUM> and support the mirror portion <NUM> in a swingable manner about the first axis a<NUM>.

The first movable frame <NUM> is a rectangular frame surrounding the mirror portion <NUM> and is connected to the mirror portion <NUM> through the first support portions <NUM> on the first axis a<NUM>. A piezoelectric element <NUM> is formed on the first movable frame <NUM> at each of positions that face with the first axis a<NUM> interposed therebetween. In such a manner, a pair of first actuators <NUM> are configured by forming two piezoelectric elements <NUM> on the first movable frame <NUM>.

The pair of first actuators <NUM> are arranged at positions that face with the first axis a<NUM> interposed therebetween. The first actuators <NUM> cause the mirror portion <NUM> to swing about the first axis a<NUM> by applying rotational torque about the first axis a<NUM> to the mirror portion <NUM>.

The second support portion <NUM> is arranged outside the first movable frame <NUM> at each of positions that face with the first axis a<NUM> interposed therebetween. The second support portions <NUM> are connected to the first movable frame <NUM> on the second axis a<NUM> and support the first movable frame <NUM> and the mirror portion <NUM> in a swingable manner about the second axis a<NUM>. In the present embodiment, the second support portions <NUM> are torsion bars that stretch along the second axis a<NUM>.

The second movable frame <NUM> is a rectangular frame surrounding the first movable frame <NUM> and is connected to the first movable frame <NUM> through the second support portions <NUM> on the second axis a<NUM>. The piezoelectric element <NUM> is formed on the second movable frame <NUM> at each of positions that face with the second axis a<NUM> interposed therebetween. In such a manner, a pair of second actuators <NUM> are configured by forming two piezoelectric elements <NUM> on the second movable frame <NUM>.

The pair of second actuators <NUM> are arranged at positions that face with the second axis a<NUM> interposed therebetween. The second actuators <NUM> cause the mirror portion <NUM> to swing about the second axis a<NUM> by applying rotational torque about the second axis a<NUM> to the mirror portion <NUM> and the first movable frame <NUM>.

The connecting portion <NUM> is arranged outside the second movable frame <NUM> at each of positions that face with the first axis a<NUM> interposed therebetween. The connecting portions <NUM> are connected to the second movable frame <NUM> on the second axis a<NUM>.

The fixed frame <NUM> is a rectangular frame surrounding the second movable frame <NUM> and is connected to the second movable frame <NUM> through the connecting portions <NUM> on the second axis a<NUM>.

In the present embodiment, the first axis a<NUM> and the second axis a<NUM> are orthogonal to each other. In the following description, a direction parallel to the first axis a<NUM> will be referred to as an X direction, a direction parallel to the second axis a<NUM> will be referred to as a Y direction, and a direction orthogonal to the first axis a<NUM> and the second axis a<NUM> will be referred to as a Z direction.

<FIG> illustrates a positional relationship among the MEMS mirror <NUM>, the half-silvered mirror <NUM>, and the eyeball EB. As illustrated in <FIG>, the MEMS mirror <NUM> is arranged such that the first axis a<NUM> that is one swinging axis passes through one focal point of the concave surface 15A that is an elliptical surface. Specifically, the MEMS mirror <NUM> is arranged such that an intersection between the first axis a<NUM> and the second axis a<NUM> matches one focal point of the concave surface 15A that is an elliptical surface. Based on this geometrical relationship, a condensing point P of the laser light L reflected by the concave surface 15A matches the other focal point of the concave surface 15A.

The AR glasses <NUM> are configured such that the center of the eyeball EB matches the condensing point P in a case where the user wears the AR glasses <NUM>. Thus, in a case where the user sees the concave surface 15A of the half-silvered mirror <NUM> in a state of wearing the AR glasses <NUM>, a part of the laser light L reflected by the concave surface 15A is incident into the eyeball EB through a pupil and is condensed to the condensing point P and then, is incident on a retina. The laser light L incident into the eyeball EB is mainly incident on a region corresponding to a macula lutea including a fovea centralis in the retina. The fovea centralis is a part in which cells for recognizing colors and shapes are concentrated and has the highest resolution in the retina. The user recognizes a video based on the laser light L projected to the retina.

In the video projected to the concave surface 15A of the half-silvered mirror <NUM> by the MEMS mirror <NUM>, the user can clearly recognize a part positioned at a center in a visual line direction.

While <FIG> illustrates a state where the concave surface 15A condenses the laser light L to the condensing point P in a YZ plane orthogonal to the first axis a<NUM>, the concave surface 15A is not limited to the YZ plane and also condenses the laser light L to the condensing point P in a plane other than the YZ plane including the two focal points.

<FIG> are diagrams for describing expansion of an eyebox by the AR glasses <NUM> according to the present embodiment. <FIG> illustrates a state where the user sees the front. In this case, the laser light L related to the video at the center of the video projected to the concave surface 15A of the half-silvered mirror <NUM> is mainly incident near the fovea centralis of the retina through the pupil. Reference numeral <NUM> denotes an image recognized by the user in a brain. Reference numeral <NUM> denotes a region (hereinafter, referred to as a high-definition region) that can be clearly recognized by the user in the entire image <NUM>. The high-definition region <NUM> corresponds to a region near the fovea centralis of the retina. In <FIG>, the high-definition region <NUM> is positioned at a center of the image <NUM>.

<FIG> illustrates a state where the user moves a visual line to a right side from the front. In this case, the laser light L related to the video on a right side of the video projected to the concave surface 15A of the half-silvered mirror <NUM> is mainly incident near the fovea centralis of the retina through the pupil. In <FIG>, the high-definition region <NUM> is positioned on a right side of the image <NUM>.

<FIG> illustrates a state where the user moves the visual line to a left side from the front. In this case, the laser light L related to the video on a left side of the video projected to the concave surface 15A of the half-silvered mirror <NUM> is mainly incident near the fovea centralis of the retina through the pupil. In <FIG>, the high-definition region <NUM> is positioned on a left side of the image <NUM>.

As illustrated in <FIG>, in the AR glasses <NUM> according to the present embodiment, since the laser light L reflected by the concave surface 15A of the half-silvered mirror <NUM> is condensed to the center of the eyeball EB, the laser light L of a region (corresponds to the high-definition region <NUM>) that the user focuses on in the video projected to the concave surface 15A is always incident near the fovea centralis of the retina even in a case where a position of the pupil is moved because the user moves the visual line. In the embodiment of the disclosed technology, while the region that can be clearly recognized by the user in the video projected to the concave surface 15A of the half-silvered mirror <NUM> is slightly narrow, the region that the user focuses on can be always clearly recognized even in a case where the visual line is moved. That is, according to the embodiment of the disclosed technology, the eyebox can be expanded with a simple configuration.

<FIG> is a diagram for describing a retinal scanning method of the related art. In the retinal scanning method of the related art, the laser light L is condensed near a center of the pupil and then, is incident on the retina. <FIG> illustrates a state where the user sees the front. In this case, since the condensing point P of the laser light L is positioned near the center of the pupil, an incidence angle of the laser light L incident on the retina is wide. That is, in the retinal scanning method of the related art, in a case where the user sees the front, a visual field is wide, and the entire image <NUM> can be recognized. On the other hand, in the retinal scanning method of the related art, in a case where the user moves the visual line, the position of the pupil deviates from the condensing point P. Thus, there is a problem that the eyebox is narrow.

<FIG> illustrates a state where the user moves the visual line to the right side from the front in the retinal scanning method of the related art. In this case, for example, the laser light incident from a right side of the pupil is blocked by an iris positioned on a left side of the pupil. Consequently, the video in a region on the right side of the image <NUM> is not seen. Since the video on the right side is not seen even in a case where the user moves the visual line to the right side in order to see the right side, the user feels stressed.

On the other hand, in a retinal scanning method according to the embodiment of the present disclosure, the laser light L is condensed to the center of the eyeball EB. Thus, even in a case where the position of the pupil is moved because the user moves the visual line, the user can always clearly recognize near a center of the visual line and does not feel stressed unlike in the related art. In the retinal scanning method according to the embodiment of the present disclosure, the visual field is slightly narrowed compared to the retinal scanning method of the related art. However, generally, a person can only clearly recognize near a center of the visual field and needs to move eyes in accordance with a region of interest in a case of, for example, reading a text. Thus, as long as the user can always clearly recognize near the center of the visual line as in the retinal scanning method according to the embodiment of the present disclosure, there is no practical problem even in a case where an edge part region cannot be clearly recognized.

Next, various modification examples of the embodiment will be described. In the embodiment, while the condensing optical system is composed of the half-silvered mirror <NUM>, various modifications can be made to the condensing optical system.

The condensing optical system is not limited to a half-silvered mirror and may be a mirror that is provided with a metal film or the like on a concave surface and highly reflects the laser light L. By using a mirror as the condensing optical system, a light scanning device that projects an immersive video can be configured.

In addition, the condensing optical system is not limited to a half-silvered mirror or a mirror and can be composed of a grating or a hologram (for example, refer to <CIT>). By using a grating or a hologram as the condensing optical system, the laser light L incident from the MEMS mirror <NUM> can be reflected in a direction other than a reflection direction of specular reflection and condensed to the center of the eyeball EB. That is, by using a grating or a holographic reflective plate as the condensing optical system, even in a case where the lenses <NUM> are flat surfaces or surfaces having a slight gradient, the condensing optical system can be provided on surfaces of the lenses <NUM>, and a degree of freedom in design of the AR glasses <NUM> is improved.

In addition, the configuration of the MEMS mirror <NUM> illustrated in the embodiment can be appropriately changed. For example, in the embodiment, while the first actuator <NUM> and the second actuator <NUM> have a ring shape, one or both of the first actuator <NUM> and the second actuator <NUM> can have a meander structure. In addition, a support member having a configuration other than a torsion bar can be used as the first support portion <NUM> and the second support portion <NUM>.

Claim 1:
Ahead mounted display comprising:
a light source (<NUM>) that emits laser light;
a mirror device (<NUM>) that includes a movable mirror (<NUM>) swinging about at least one axis and directionally changes the laser light emitted from the light source (<NUM>) by reflecting the laser light using the movable mirror (<NUM>); and
a condensing optical system configured to condense the laser light directionally changed by the mirror device (<NUM>) to a centre of an eyeball of a user wearing the head mounted display, wherein the centre of the eyeball of the user is positioned away from the centre of the pupil of the eyeball of the user, wherein the condensing optical system is a half-silvered mirror or a mirror (<NUM>) having a concave surface (15A) and configured to condense at least a part of the laser light directionally changed by the mirror device (<NUM>) to the centre of the eyeball by reflecting at least the part of the laser light using the concave surface (15A), wherein the concave surface (15A) is an elliptical surface, and
wherein the head mounted display is configured such that a swinging axis of the movable mirror (<NUM>) is positioned at one focal point of the elliptical surface, and the centre of the eyeball is positioned at the other focal point of the elliptical surface.