Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B30/00—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
  • G02B30/50—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images the image being built up from image elements distributed over a three-dimensional [3D] volume, e.g. voxels
  • G02B30/56—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images the image being built up from image elements distributed over a three-dimensional [3D] volume, e.g. voxels by projecting aerial or floating images

Definitions

• This disclosure relates to an aerial image display device.
• an aerial image display device is known, for example, as described in Patent Document 1.
• the aerial image display device of the present disclosure is an aerial image display device including a display unit and an optical system that forms an image light emitted from the display unit into a real aerial image
• the area S1 is obtained by integrating the first modulation transfer function of the aerial image formed by the optical system on the spatial frequency axis
• the optical system is an ideal optical system having a diffraction-limited resolution
• the area S2 is obtained by integrating the second modulation transfer function of the ideal aerial image formed by the ideal optical system on the spatial frequency axis
• the ratio S1/S2 of the area S1 to the area S2 is 0.58 or more.
• FIG. 1 is a cross-sectional view showing a configuration of an aerial image display device according to an embodiment of the present disclosure.
• 11 is a cross-sectional view showing a configuration of an aerial image display device according to another embodiment of the present disclosure.
• 1 is a graph showing an example of a modulation transfer function.
• 2 is a diagram showing an example of an aerial image visually recognized by a user of the aerial image display device of FIG. 1 .
• 4A and 4B are diagrams for explaining the definition of the curvature of a first concave mirror.
• 1 is a perspective view showing a measurement system for calculating a modulation transfer function of an aerial image formed by an aerial image display device.
• FIG. 13 is a diagram showing an example of a test pattern for calculating a modulation transfer function.
• FIG. 2 is a diagram showing a captured image of a test pattern captured by an imaging device.
• 4 is a partial enlarged view showing an image of a test pattern captured by an imaging device.
• FIG. 10 is a graph showing a luminance distribution waveform calculated from the captured image of FIG. 9 .
• FIG. 13 is a diagram showing another example of the test pattern for calculating the modulation transfer function.
• 4 is a partial enlarged view showing an image of a test pattern captured by an imaging device.
• FIG. 11A and 11B are side views illustrating a defocus operation for the imaging apparatus.
• 1 is a partial enlarged view showing an example of a captured image of a test pattern captured by an imaging device.
• FIG. 1 is a partial enlarged view showing an example of a captured image of a test pattern captured by an imaging device
• FIG. 2 is a diagram showing an example of a captured image of a test pattern captured by an imaging device.
• 1 is a graph showing the focal position of each imaging region.
• FIG. 18 is a diagram for explaining the optical axis deviation corresponding to the graph in FIG. 17 .
• 1 is a graph showing the focal position of each imaging region.
• FIG. 20 is a diagram for explaining the optical axis deviation corresponding to the graph in FIG. 19 .
• 1A and 1B are diagrams illustrating a rotation operation for the imaging device.
• 13 is a graph showing the relationship between the MTF area S1 of an aerial image formed by an optical system and the sharpness of the luminance distribution waveform of the aerial image (width ratio W/Q: (half width)/(quarter width)) when the F-number of the imaging device is 3.
• 13 is a graph showing the relationship between the MTF area S1 of an aerial image formed by an optical system and the sharpness of the luminance distribution waveform of the aerial image (width ratio W/Q: (half width)/(quarter width)) when the F-number of the imaging device is 8.
• Conventional aerial image display devices are configured to focus the image light emitted from the display panel as a real aerial image using optical components such as polarizing filters and beam splitters. Conventional aerial image display devices can sometimes result in reduced resolution and brightness of the aerial image.
• the drawings referred to below are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.
• a Cartesian coordinate system XYZ is defined in some of the drawings.
• the X-axis direction is also referred to as the first direction or height direction.
• the Y-axis direction is also referred to as the second direction or width direction (horizontal direction, lateral direction).
• the Z-axis direction is also referred to as the third direction or depth direction.
• Figures 1 to 23 are diagrams or graphs illustrating an aerial image display device according to one embodiment of the present disclosure.
• the second band-shaped image black image
• Figures 7 to 9, 11, 12, and 14 to 16 the second band-shaped image (black image) is shown at a higher brightness than its actual brightness to facilitate illustration.
• the aerial image display device 2 includes a display unit 3 and an optical system 5.
• the display unit 3 includes a display panel 4.
• the display panel 4 has a display surface 4a, and displays an image that is formed as an aerial image R on the display surface 4a. That is, the display panel 4 emits image light Lp that is formed as an aerial image R from the display surface 4a.
• the display panel 4 may be a transmissive display panel or a self-luminous display panel. If the display panel 4 is a transmissive display panel, the display unit 3 may include an illuminator such as a backlight. If the display panel 4 is a self-luminous display panel, the display unit 3 does not need to include an illuminator.
• the transmissive display panel may include a liquid crystal panel.
• the transmissive display panel may have a known liquid crystal panel configuration.
• various liquid crystal panels such as IPS (In-Plane Switching) type, FFS (Fringe Field Switching) type, VA (Vertical Alignment) type, ECB (Electrically Controlled Birefringence) type, etc. may be used.
• the transmissive display panel includes MEMS (Micro Electro Mechanical Systems) shutter type display panels.
• the self-luminous display panel may include a plurality of self-luminous elements.
• various self-luminous elements such as LEDs (Light Emitting Diodes), organic EL (Electro Luminescence), inorganic EL, etc. may be used.
• the optical system 5 focuses the image light Lp emitted from the display unit 3 into a real aerial image R.
• the optical system 5 may be composed of a reflective member such as a concave mirror or a convex mirror. As shown in FIG. 1, the optical system 5 may be composed of a first concave mirror 5a, a convex mirror 5b, and a second concave mirror 5c.
• the first concave mirror 5a is configured to reflect the image light Lp emitted from the display unit 3 in a direction different from the direction toward the display unit 3.
• the first concave mirror 5a may be a free-form concave mirror.
• the first concave mirror 5a is not limited to being a free-form concave mirror, and may be a spherical concave mirror or an aspherical concave mirror.
• the convex mirror 5b is configured to reflect the image light Lp reflected by the first concave mirror 5a in a direction different from the direction toward the first concave mirror 5a.
• the convex mirror 5b may be a free-form convex mirror.
• the convex mirror 5b is not limited to being a free-form convex mirror, and may be a spherical convex mirror or an aspherical convex mirror.
• the second concave mirror 5c is configured to reflect the image light Lp reflected by the convex mirror 5b in a direction different from the direction toward the convex mirror 5b, forming an aerial image R.
• the second concave mirror 5c may be a free-form concave mirror.
• the second concave mirror 5c is not limited to being a free-form concave mirror, and may be a spherical concave mirror or an aspherical concave mirror.
• the aerial image display device 2 may be configured such that the first concave mirror 5a and the second concave mirror 5c face each other in a tilted state, the display panel 4 is located between the first concave mirror 5a and the second concave mirror 5c, and the tilt of the display surface 4a of the display panel 4 with respect to the reflecting surface (also called the first reflecting surface) 5ar of the first concave mirror 5a is smaller than the tilt of the display surface 4a of the display panel 4 with respect to the reflecting surface (also called the second reflecting surface) 5cr of the second concave mirror 5c.
• the aerial image display device 2 Since the first concave mirror 5a and the second concave mirror 5c face each other in a tilted state, and the display panel 4 is located between the first concave mirror 5a and the second concave mirror 5c, the aerial image display device 2 is made smaller. In particular, the vertical dimension of the aerial image display device 2 (X-axis direction in FIG. 1) is reduced.
• the display surface 4a of the display panel 4 and the first reflecting surface 5ar of the first concave mirror 5a become nearly parallel.
• the angle of incidence of the light beam of the image light Lp emitted from the display surface 4a with respect to the first reflecting surface 5ar becomes smaller, and the distortion of the aerial image R can be reduced and the brightness of the aerial image R can be increased.
• the inclination of the display surface 4a of the display panel 4 with respect to the first reflecting surface 5ar of the first concave mirror 5a may be defined as an inclination angle between the display surface 4a (or a virtual surface 4ai including the display surface 4a in space) and a tangent plane (or a virtual surface 5ai including the tangent plane in space) that is in contact with the apex 5ap of the curvature of the first reflecting surface 5ar.
• the inclination of the display surface 4a of the display panel 4 with respect to the second reflecting surface 5cr of the second concave mirror 5c may be defined as the inclination angle between the display surface 4a (or a virtual surface 4ai in space that includes the display surface 4a) and a tangent plane (or a virtual surface 5ci in space that includes the tangent plane) that is tangent to the apex 5cp of the curvature of the second reflecting surface 5cr.
• the convex mirror 5b may be located between the first concave mirror 5a and the second concave mirror 5c.
• the optical system 5 of the aerial image display device 2 is made smaller.
• the vertical dimension of the optical system 5 is made smaller.
• the convex mirror 5b may be closer to the first concave mirror 5a and the second concave mirror 5c than the display panel 4.
• the optical system 5 of the aerial image display device 2 is made even smaller.
• the horizontal dimension of the optical system 5 (Z-axis direction in FIG. 1) is made smaller.
• the aerial image display device 2 is not limited to the configuration shown in FIG. 1.
• the optical system 5 may be composed of a first concave mirror 5d and a second concave mirror 5e, as shown in FIG. 2.
• the first concave mirror 5d is configured to reflect the image light Lp emitted from the display unit 3 in a direction different from the direction toward the display unit 3.
• the first concave mirror 5d may be a free-form concave mirror.
• the first concave mirror 5d is not limited to being a free-form concave mirror, and may be a spherical concave mirror or an aspherical concave mirror.
• the second concave mirror 5e is configured to reflect the image light Lp reflected by the first concave mirror 5d in a direction different from the direction toward the first concave mirror 5d, and form an aerial image R.
• the second concave mirror 5e may be a free-form concave mirror.
• the second concave mirror 5e is not limited to being a free-form concave mirror, and may be a spherical concave mirror or an aspherical concave mirror.
• the aerial image display device 2 may be configured such that the curvature of the first concave mirror 5d is greater than the curvature of the second concave mirror 5e, the first concave mirror 5d and the second concave mirror 5e face each other in a tilted state, and the display panel 4 is located between the first concave mirror 5d and the second concave mirror 5e. Since the curvature of the first concave mirror 5d is greater than the curvature of the second concave mirror 5e, the display panel 4 can be positioned closer to the first concave mirror 5d. As a result, the aerial image display device 2 is made smaller. In particular, the horizontal dimension of the aerial image display device 2 is reduced. Since the display panel 4 is located between the first concave mirror 5d and the second concave mirror 5e, the aerial image display device 2 is made even smaller. In particular, the vertical dimension of the aerial image display device 2 is reduced.
• the free-form surface that defines the reflecting surface of the free-form concave mirror and the reflecting surface of the free-form convex mirror may be an XY polynomial surface (also called an SPS XYP surface) defined by the following formulas (1) and (2).
• the XY polynomial surface is expanded into a polynomial of up to the 10th order that is added to the reference conic surface. Therefore, in formulas (1) and (2), the sum of m and n is 10 or less.
• z is the sag of the surface parallel to the z axis (optical axis)
• c is the vertex curvature
• k is the conic constant
• Cj is the coefficient of the monomial xmyn .
• the aerial image display device 2 may include a housing 6, as shown in Figures 1 and 2.
• Components 2a of the aerial image display device 2, such as the display unit 3 and the optical system 5, may be located within the housing 6.
• the components 2a may include a circuit board, wiring, cables, heat dissipation components such as a heat sink, a holding member for holding the optical system 5, an adjustment member for adjusting the position of the optical system 5, etc.
• the housing 6 may be made of, for example, a resin material, a metal material, a ceramic material, etc.
• At least a portion of the housing 6 that faces the user of the aerial image display device 2 is configured as an image light emitting section 6a.
• Image light Lp that is focused as an aerial image R is emitted from inside the housing 6 to outside the housing 6 via the image light emitting section 6a.
• the image light emitting section 6a may be configured to include, for example, a light-shielding film or light-shielding glass. In this case, when using the aerial image display device 2, it becomes difficult for the user 20 to see the components 2a located inside the housing 6, and the visibility of the aerial image R can be improved.
• the resolution of the aerial image R can be expressed by the modulation transfer function (MTF).
• the modulation transfer function is a performance index for evaluating the resolution of the optical system 5, and can be used as a resolution index for comparing the high and low resolution of the aerial image R.
• the modulation transfer function may be normalized so that the maximum value is 1. In this case, the closer the value of the modulation transfer function is to 1, the higher the resolution of the optical system 5 (i.e., the resolution of the aerial image R).
• the value of the modulation transfer function itself may be used as the performance index of the optical system 5, but the resolution of the optical system 5 (i.e., the resolution of the aerial image R) can be evaluated with high accuracy by using the area obtained by integrating the modulation transfer function on the spatial frequency axis as the performance index of the optical system 5.
• the aerial image R formed by the optical system 5 is an aerial image with degraded resolution due to the above factors.
• An ideal optical system has the same configuration as the optical system 5, but has a resolution at the diffraction limit.
• an ideal optical system is an optical system in which the degradation of resolution is limited only to the degradation that inevitably occurs due to the diffraction of light.
• An ideal aerial image formed by an ideal optical system is an aerial image in which the degradation of resolution is theoretically minimized.
• the diffraction limit even when light from a point light source is geometrically optically concentrated at a single focal point by an aberration-free optical system in a vacuum, for example, the light actually spreads to a certain size due to the wave properties of the light.
• FIG. 3 is a graph showing an example of a modulation transfer function.
• the modulation transfer function K1 of the aerial image R formed by the optical system 5 (hereinafter also referred to as the first modulation transfer function) is shown by a dashed line
• the modulation transfer function K2 of an ideal aerial image formed by an ideal optical system (hereinafter also referred to as the second modulation transfer function) is shown by a solid line.
• the first modulation transfer function K1 is smaller than the second modulation transfer function K2.
• the area S1 obtained by integrating the first modulation transfer function K1 on the spatial frequency axis (hereinafter also referred to as the MTF area) is smaller than the area S2 obtained by integrating the second modulation transfer function K2 on the spatial frequency axis, and the area ratio S1/S2 is smaller than 1. It can be said that the closer the area ratio S1/S2 is to 1, the higher the resolution of the aerial image R actually formed by the aerial image display device 2.
• the aerial image display device 2 is configured such that when the area S1 is the area obtained by integrating the first modulation transfer function K1 of the aerial image R formed by the optical system 5 on the spatial frequency axis, the optical system 5 is an ideal optical system having a diffraction-limited resolution, and the area S2 is the area obtained by integrating the second modulation transfer function K2 of the ideal aerial image formed by the ideal optical system on the spatial frequency axis, the ratio S1/S2 of the area S1 to the area S2 is 0.85 or more. Therefore, the aerial image display device 2 can suppress degradation of resolution.
• the modulation transfer function can be calculated using a measurement system 1 described below.
• the measurement system 1 includes an imaging device 7 capable of capturing an aerial image R.
• the modulation transfer function can be calculated based on the imaging data of the aerial image R output from the imaging device 7.
• the first modulation transfer function K1 and the second modulation transfer function K2 may be normalized so that the maximum value is 1.
• the area S1 obtained by integrating the first modulation transfer function K1 on the spatial frequency axis may be 6 or more. This can improve the resolution when the eye 20e of the user 20 views the aerial image R.
• the area S1 obtained by integrating the first modulation transfer function K1 on the spatial frequency axis may be 12.7 or more. This can allow the user 20 to view the aerial image R with reduced degradation in resolution and reduced optical axis deviation.
• the optical axis deviation refers to the deviation between the actual optical axis direction Da of the aerial image R formed by the aerial image display device 2 and the designed optical axis direction Dad of the aerial image R formed by the aerial image display device 2 (see Figures 1 and 2).
• FIG. 23 is a graph showing the relationship between the MTF area S1 of the aerial image R formed by the optical system 5 and the width ratio W/Q, which represents the sharpness of the luminance distribution waveform of the aerial image R, when the F-number (aperture value) of the imaging device 7 is 8.
• the luminance distribution waveform is also called the line spread function (LSF) shown in FIG. 10.
• W is the half-width of the LSF shown in FIG. 10
• Q is the quarter-width (hereinafter also referred to as the half-width or quarter-width) of the LSF shown in FIG. 10.
• the width ratio W/Q is (half-width)/(quarter-width), which is the ratio of the half-width W to the quarter-width Q of the line spread function, as shown in FIG. 10.
• the value on the upper horizontal axis indicates the value of the MTF area S1
• the value on the lower horizontal axis indicates the value of the area ratio S1/S2
• the value of the area S2 is 7.25.
• the sharpness of the luminance distribution waveform tends to be low and the value of the MTF area S1 of the aerial image R tends to be small overall.
• the smaller the value of the MTF area S1 of the aerial image R that is, the lower the contrast of the aerial image R, the lower the sharpness of the luminance distribution waveform tends to be.
• the numerical value on the upper horizontal axis indicates the value of the MTF area S1
• the numerical value on the lower horizontal axis indicates the value of the area ratio S1/S2
• the value of the area S2 is 14.9.
• the sharpness of the luminance distribution waveform tends to be high, and the value of the MTF area S1 of the aerial image R tends to be large overall.
• the larger the value of the MTF area S1 of the aerial image R that is, the higher the contrast of the aerial image R, the higher the sharpness of the luminance distribution waveform tends to be.
• S1/S2 may be 0.85 or more.
• the aerial image display device 2 can reduce the distortion of the aerial image R formed by the optical system 5 to 5% or less.
• FIG. 4 shows a simulation result of the aerial image R viewed by the user 20 of the aerial image display device 2 of FIG. 1.
• the aerial image R is shown as an aerial image with a lattice pattern, and coordinate axes indicating the direction and amount of distortion are shown.
• the solid line shows the aerial image R viewed by the user 20, and the dashed line shows a virtual aerial image IR without distortion.
• the distortion of the aerial image R can include distortion in the planar direction (direction parallel to the paper surface) and distortion in the depth direction (direction perpendicular to the paper surface), but FIG. 4 shows only distortion in the planar direction. Note that in FIG. 4, unlike FIGS. 1 and 2, the X-axis direction is the horizontal direction and the Y-axis direction is the height direction.
• distortion of the aerial image R is likely to occur on the outer periphery of the aerial image R, and distortion is particularly likely to be large at the four corners of the aerial image R (lower right corner LR, upper right corner UR, lower left corner LL, and upper left corner UL).
• Table 1 shows the distortion from the aerial image IR at the corners LR, UR, LL, and UL.
• the aerial image display device 2 can suppress distortion at the corners LR, UR, LL, and UL to within ⁇ 5%.
• the + (plus) direction of the X direction is the right direction in FIG. 4, and the - (minus) direction of the X direction is the left direction in FIG. 4.
• the + (plus) direction of the Y direction is the upward direction in FIG. 4, and the - (minus) direction of the Y direction is the downward direction in FIG. 4.
• the distortion of the aerial image R in each of the X and Y directions is a positive value when it is distorted outward from the aerial image IR, and a negative value when it is distorted inward from the aerial image IR.
• the outward direction in the X direction (rightward: expanding direction) is the + (plus) direction
• the inward direction in the X direction (leftward: shrinking direction) is the - (minus) direction
• the outward direction in the Y direction (downward: expanding direction) is the + (plus) direction
• the inward direction in the Y direction (upward: shrinking direction) is the - (minus) direction.
• the upper right corner UR, the lower left corner LL, and the upper left corner UL The same applies to the following tables showing distortion of the aerial image R.
• the distortion at the corners LR, UR, LL, and UL is calculated as follows.
• the distortion in the X direction at the corners LR, UR, LL, and UL is defined as the length of deviation in the X direction relative to the length LX of the top side (the bottom side is the same length as the top side) of the rectangular aerial image IR. Because the length of the bottom side of the aerial image IR is the same as the length LX of the top side, the length LX of the top side is used as the reference.
• the distortion in the X direction at the corner UR is defined as the length of deviation ⁇ XUR in the X direction from the upper right corner CUR of the aerial image IR relative to the length LX of the top side.
• the distortion in the X direction at the corner UR is defined as ( ⁇ XUR/LX) x 100 (%). Because the corner UR is distorted inward of the aerial image IR in the X direction, the value is - (negative). The distortion in the X direction at the corners LR, LL, and UL is defined similarly. If the aerial image IR has a shape other than rectangular, the reference length in the X direction may be the average length or the maximum length.
• the distortion in the Y direction of the corners LR, UR, LL, and UL is specified by the deviation length in the Y direction relative to the length LY of the right side (the left side is the same length as the right side) of the rectangular aerial image IR. Since the length of the left side of the aerial image IR is the same as the length LY of the right side, the length LY of the right side is used as the reference.
• the distortion in the Y direction of the corner UR is specified by the deviation length ⁇ YUR in the Y direction from the upper right corner CUR of the aerial image IR relative to the length LY of the right side. In other words, the distortion in the Y direction of the corner UR is specified by ( ⁇ YUR/LY) ⁇ 100(%).
• the corner UR is distorted inward of the aerial image IR in the Y direction, it has a negative (negative) value.
• the distortion in the Y direction of the corners LR, LL, and UL is specified in the same way. If the aerial image IR is a shape other than rectangular, the reference length in the Y direction may be the average length or the maximum length.
• the curvature Sa of the first concave mirror 5a may be about 0.35 to 0.45
• the curvature Sb of the convex mirror 5b may be about 0.15 to 0.25
• the curvature Sc of the second concave mirror 5c may be about 0.25 to 0.35.
• the area ratio S1/S2 can be 0.85 or more while suppressing the distortion of the aerial image R to 5% or less.
• the curvature Sd of the first concave mirror 5d may be about 0.2 to 0.3
• the curvature Se of the second concave mirror 5e may be about 0.05 to 0.15.
• the area ratio S1/S2 can be 0.85 or more while suppressing the distortion of the aerial image R to 5% or less.
• the curvatures Sa, Sb, Sc, Sd, and Se are not limited to the above ranges because they can change depending on the size, shape, and angle of view (spread of light) of the display panel 4.
• the curvature Sa of the first concave mirror 5a is defined by DMAX/H, where the length of a line segment LS that passes through the center of the reflecting surface 5aa of the first concave mirror 5a and connects both ends of the reflecting surface 5aa is 2 x H, and the maximum value of the length (also called the maximum depth) between a point on the reflecting surface 5aa and the line segment LS in the direction along the optical axis OA is DMAX .
• the maximum value of DMAX /H when the position of the cross section is changed may be taken as the curvature Sa.
• the curvatures Sb, Sc, Sd, and Se are also defined in the same way as the curvature Sa.
• the aerial image display device 2 can achieve a brightness of 800 cd/m2 or more for the aerial image R formed by the optical system 5.
• the aerial image display device 2 has a high utilization rate of the image light Lp because the optical system 5 is composed only of reflective members and does not include optical members that transmit part of the incident light, such as polarizing filters and beam splitters. Therefore, the aerial image display device 2 can form a high-brightness aerial image R while suppressing an increase in power consumption.
• the brightness of the aerial image R may be measured by a commercially available luminance meter.
• the brightness of the aerial image R may be measured by a luminance meter placed at the position of the imaging device 7 (see Figure 6).
• the modulation transfer function of the aerial image R can be calculated using the measurement system 1. As shown in FIG. 6, the measurement system 1 includes an imaging device 7, a control unit 8, and an acquisition unit 14.
• the imaging device 7 is assumed to be the eye 20e of the user 20 (see Figures 1 and 2), and captures the aerial image R formed by the aerial image display device 2.
• the imaging device 7 is located away from the aerial image display device 2 in the design optical axis direction Dad of the aerial image display device 2.
• the imaging device 7 captures the aerial image R formed by the aerial image display device 2 in the design optical axis direction Dad of the aerial image display device 2.
• the design optical axis direction Dad refers to the design optical axis direction of the aerial image R formed by the aerial image display device 2.
• the design optical axis direction Dad may be, for example, a direction perpendicular to the width direction of the housing 6, or a direction perpendicular to the emission surface of the image light emission unit 6a.
• the aerial image display device 2 is disposed so that the design optical axis direction Dad coincides with the depth direction.
• the imaging direction 7d of the imaging device 7 is not limited to the design optical axis direction.
• the control unit 8 may control the first rotation device 12 to rotate the imaging device 7 around a predetermined rotation axis. That is, the control unit 8 may control the imaging device 7 to capture the aerial image R in a direction different from the design optical axis direction (depth direction).
• the imaging device 7 includes an imaging element.
• the imaging element may be, for example, a CCD (Charge Coupled Device) imaging element or a CMOS (Complementary Metal Oxide Semiconductor) imaging element.
• the imaging device 7 may be a camera (for example, a CCD camera) including multiple imaging elements and optical elements such as an objective lens.
• the imaging device 7 may be capable of changing the aperture value (F-number).
• the imaging device 7 may be capable of changing the aperture value within a range of 2 to 22.
• the control unit 8 may function as a control unit of the measurement system 1.
• the control unit 8 may be connected to each component of the measurement system 1 and control each component.
• the control unit 8 may also function as a control unit of the aerial image display device 2 when calculating the modulation transfer function of the aerial image R.
• the control unit 8 may control, for example, the aerial image R formed by the aerial image display device 2.
• the control unit 8 may include one or more processors.
• the processor may include at least one of a general-purpose processor configured to load a specific program and execute a specific function, and a dedicated processor specialized for a specific process.
• the dedicated processor may include an ASIC (Application Specific Integrated Circuit).
• the processor may include a PLD (Programmable Logic Device).
• the PLD may include an FPGA (Field-Programmable Gate Array).
• the control unit 8 may include at least one of a SoC (System-on-a-Chip) and a SiP (System In a Package) configured to cooperate with one or more processors.
• the acquisition unit 14 may store image data of the captured image generated by the imaging device 7.
• the control unit 8 may acquire image data of the captured image via the acquisition unit 14.
• the imaging device 7 When the imaging device 7 generates an captured image, it may automatically output image data of the captured image to the acquisition unit 14.
• the acquisition unit 14 may be a temporary storage device such as a buffer memory.
• the method of transmitting and receiving signals between the control unit 8 and the imaging device 7, the method of transmitting and receiving signals between the acquisition unit 14 and the imaging device 7, and the method of transmitting and receiving signals between the acquisition unit 14 and the control unit 8 may use at least one of a wired communication method, a wireless communication method, an infrared communication method, etc.
• the control unit 8 controls the aerial image display device 2 to form a test pattern (hereinafter, simply referred to as an aerial image) 9 in the air as shown in Figs. 6 and 7.
• Fig. 7 shows a test pattern 9 without blurring (resolution degradation).
• the test pattern 9 may be a repeated pattern of a first band-shaped image 9a and a second band-shaped image 9b.
• the first band-shaped image 9a and the second band-shaped image 9b may be elongated images in the vertical direction (X-axis direction).
• the test pattern 9 may include at least three first band-shaped images 9a.
• first band-shaped image 9a is a white image and the second band-shaped image 9b is a black image, but this is not limited to this.
• the first band-shaped image 9a and the second band-shaped image 9b may differ in at least one of brightness and color.
• the imaging device 7 may be tilted by about 3° to 5° around a rotation axis parallel to the depth direction (Z-axis direction) in the height direction of the imaging device 7 (e.g., a direction perpendicular to the top surface of the imaging device 7).
• the number of samples taken when calculating the modulation transfer function of the test pattern 9 can be increased, making it possible to calculate the modulation transfer function of the test pattern 9 with high accuracy.
• Figure 8 shows an example of an overall image of the test pattern 9 formed by the aerial image display device 2.
• the control unit 8 controls the imaging device 7 to capture at least one imaging portion in the test pattern 9.
• the at least one imaging portion may be, for example, at least one of the multiple imaging portions F1 to F7 shown in Figure 8.
• the at least one imaging portion may be multiple imaging portions F3 to F5, or multiple imaging portions F1 to F7.
• the imaging device 7 captures imaging portions F1 to F7 in the test pattern 9. Note that “to” means “up to,” and the same applies below.
• the imaging portion F4 may be located near the center of the imaging plane Rp (X-axis direction and Y-axis direction) of the aerial image R.
• the imaging portions F3 to F5 may be aligned in a predetermined direction in the imaging plane Rp of the aerial image 9.
• the predetermined direction may be, but is not limited to, the Y-axis direction (width direction).
• the predetermined direction may be the X-axis direction (up-down direction, height direction) or a direction inclined from the X-axis direction and Y-axis direction (diagonal direction).
• the imaging portions F1, F2, F6, and F7 may be located at the four corners of the test pattern 9, respectively, as shown in FIG. 8. In the following, unless otherwise specified, a case will be described in which the imaging portions F3 to F5 are aligned in the Y-axis direction (width direction) in the imaging plane of the aerial image 9.
• the imaging device 7 captures a plurality of imaging portions F1 to F7 of the test pattern 9 and outputs image data of a plurality of captured images P1 to P7.
• the plurality of captured images P1 to P7 are images of a plurality of imaging portions F1 to F7, respectively.
• the test pattern 9 may be configured so that each of the plurality of captured images P1 to P7 includes at least one image of the first strip-shaped image 9a (white image portion in FIG. 7).
• the test pattern 9 may be configured so that each of the plurality of captured images P1 to P7 includes an image of one first strip-shaped image 9a, as shown in FIG. 9.
• FIG. 9 shows the captured image P3, but the same is true for the captured images P1, P2, P4 to P7.
• the distance between the imaging device 7 and the test pattern 9 in the depth direction may be set to a predetermined imaging distance (also referred to as the initial setting distance).
• the initial setting distance may be, for example, 300 mm to 700 mm, or 500 mm.
• the distance between the imaging device 7 and the aerial image 9 may be the distance between the imaging device 7 and the vicinity of the center of the aerial image 9 (for example, the imaging part F4).
• the focal length of the imaging device 7 is fixed to a predetermined focal length.
• the predetermined focal length may be the same as the initial setting distance. In the following, unless otherwise specified, the distance between the imaging device 7 and the aerial image 9 is set to the initial setting distance.
• control unit 8 may control the moving device 11 to change the distance between the imaging device 7 and the aerial image 9 from the initial setting distance. That is, the control unit 8 may perform a defocus operation to make the distance between the imaging device 7 and the aerial image 9 and the focal length of the imaging device 7 different.
• the control unit 8 may control the imaging device 7 to set the aperture value to a value greater than 3, or may control the imaging device 7 to set the aperture value to a value equal to or less than 3.
• the aperture value of the imaging device 7 By setting the aperture value of the imaging device 7 to a relatively large value (e.g., 8), the resolution when the eye 20e of the user 20 visually recognizes the test pattern 9 can be evaluated.
• the aperture value of the imaging device 7 By setting the aperture value of the imaging device 7 to a relatively small value (e.g., 3), the depth of field (also called the focal depth of field) of the imaging device 7 can be made shallow (shortened). That is, the range in which the subject is in focus in the depth direction can be made small (narrowed).
• the position of the subject i.e., the multiple imaging parts F3, F4, F5 in the depth direction can be accurately measured, and the modulation transfer function can be accurately calculated.
• the control unit 8 acquires image data of the multiple captured images P1 to P7 from the imaging device 7 via the acquisition unit 14.
• the control unit 8 scans the luminance values of the pixels arranged in the width direction (left and right direction in FIG. 9) for the multiple captured images P1 to P7, performs binning processing, and calculates the luminance distribution waveforms LSF1 to LSF7 as shown in FIG. 10.
• the luminance distribution waveforms LSF1 to LSF7 refer to the luminance distribution waveforms calculated from the image data of the captured images P1 to P7.
• the luminance distribution waveforms LSF1 to LSF7 are pulse-shaped waveforms that represent the change in luminance depending on the position in the Y-axis direction. The horizontal axis in FIG.
• FIG. 10 represents the change in position in the Y-axis direction.
• FIG. 10 shows the maximum value (peak value) of the luminance distribution waveform at the position of the 30th pixel among multiple pixels (for example, 60 pixels) in the Y-axis direction.
• the luminance distribution waveform is also called a line spread function (LSF).
• the line spread functions LSF1 to LSF7 have a substantially Gaussian shape as shown in FIG. 10.
• the method of measuring the optical axis direction based on the characteristic values of the LSF is also referred to as the LSF method.
• the control unit 8 calculates modulation transfer functions MTF1 to MTF7 such as the first modulation transfer function K1 shown in Fig. 3 by Fourier transforming each of the line spread functions LSF1 to LSF7 as shown in the following formula (3).
• the Fourier transform is an operation for converting, for example, a function represented by a pulse-like waveform into a curve represented by continuous values in the frequency domain (a continuous curve represented by a sine waveform curve, a cosine waveform curve, or a composite curve of these).
• LSF(x) collectively represents the line spread functions LSF1 to LSF7 as a function of position x in the captured images P1 to P7.
• MTF( ⁇ ) collectively represents the modulation transfer functions MTF1 to MTF7 as a function of spatial frequency ⁇ .
• C is a constant for normalizing MTF(0) to "1".
• the MTF( ⁇ ) can be said to be an index representing the resolution based on the contrast of the captured images P1 to P7.
• the modulation transfer functions MTF1 to MTF3 and MTF5 to MTF7 may be replaced with finite values, in which case the processing load on the control unit 8 can be reduced.
• a method such as discrete Fourier transform or fast Fourier transform may be used.
• the control unit 8 measures areas A1 to A7 obtained by integrating the modulation transfer functions MTF1 to MTF7 on the spatial frequency axis, respectively, as expressed in the following formula (4).
• the integral interval in formula (4) may be replaced with a finite interval (for example, a range of 0/mm to 18/mm), in which case the processing load on the control unit 8 can be reduced.
• the control unit 8 may set the average value of the areas A1 to A7 as the area S1 of the first modulation transfer function K1. In this case, the high or low of the average resolution over the entire aerial image R can be evaluated.
• the control unit 8 may set the weighted average of the areas A1 to A7 as the area S1 of the first modulation transfer function K1. In this case, the high or low of the resolution near the center of the aerial image R can be evaluated by increasing the weighting of the areas A3, A4, and A5. Alternatively, the high or low of the resolution at the corners of the aerial image R can be evaluated by increasing the weighting of the areas A1, A2, A6, and A7.
• the control unit 8 may set the minimum value A MIN of the areas A1 to A7 as the area S1 of the first modulation transfer function K1. In this case, the high or low of the resolution over the entire aerial image R can be evaluated.
• the modulation transfer functions MTF1 to MTF7 do not have to be calculated by Fourier transforming the line spread functions LSF1 to LSF7, respectively.
• the modulation transfer functions MTF1 to MTF7 may be calculated directly from the image data of the captured images P1 to P7, respectively, using the chart method.
• the control unit 8 controls the aerial image display device 2 to form a test pattern (hereinafter, also simply referred to as an aerial image) 9' as shown in Figure 11.
• Figure 11 shows an ideal aerial image 9' without blurring (resolution degradation) and optical axis misalignment.
• the aerial image 9' is configured so that each of the imaging portions F1 to F7 includes multiple square wave charts 9c, 9d, 9e, and 9f with different spatial frequencies (pitch of the white image portion). Therefore, each of the captured images P1 to P7 includes images of multiple square wave charts 9c to 9f with different spatial frequencies ⁇ , as shown in Figure 12.
• the control unit 8 controls the imaging device 7 to capture the aerial image 9', generate captured images P1 to P7 by capturing the imaging portions F1 to F7, and output image data of the captured images P1 to P7.
• the imaging device 7 does not need to be inclined with respect to the upper surface 10a of the device stand 10 when capturing the aerial image 9'.
• control unit 8 normalizes the contrast ratio c ⁇ of each spatial frequency ⁇ with the contrast ratio c ⁇ of the lowest spatial frequency ⁇ to calculate the square wave response function (Square Wave Response Function: SWRF).
• SWRF Square Wave Response Function
• the control unit 8 converts the square wave response function into a sine wave response function and calculates the modulation transfer functions MTF1 to MTF7.
• Coltman's formula may be used. The Coltman's formula may use up to the fourth term or up to the twelfth term.
• the above describes a method for calculating the first modulation transfer function of the aerial image 9 actually formed by the aerial image display device 2.
• the second modulation transfer function K2 of the ideal aerial image formed by an ideal optical system may be calculated by simulation.
• a simulated image that mimics the ideal aerial image may be placed on the imaging plane Rp, and the second modulation transfer function may be calculated based on image data obtained by the imaging device 7 capturing the simulated image.
• the simulated image may be a repeating pattern of a first band-shaped image 9a and a second band-shaped image 9b, similar to the test pattern 9 shown in Figures 7 and 8.
• a misalignment (hereinafter also referred to as optical axis misalignment) may occur between the optical axis direction Da of the aerial image R formed by the aerial image display device 2 and the design optical axis direction Dad.
• optical axis misalignment occurs, a bias occurs in the display quality such as brightness and resolution within the imaging plane Rp of the aerial image R, and it may not be possible to accurately calculate the modulation transfer functions MTF1 to MTF7.
• the measurement system 1 may be configured to measure the optical axis misalignment of the aerial image display device 2.
• the measurement system 1 may be configured to calibrate the optical axis misalignment of the aerial image display device 2.
• the following describes the measurement system 1 that measures the optical axis deviation of the aerial image display device 2.
• the measurement system 1 may include a moving device 11 that moves the imaging device 7 along the depth direction (Z direction).
• the moving device 11 is configured to be able to move the imaging device 7 in a predetermined distance ⁇ Z unit.
• the predetermined distance ⁇ Z may be, for example, about 1 mm to 5 mm, or about 1 mm to 2 mm.
• the moving device 11 includes, for example, a rail 11r, a holding member (also called a support member) 11h, and a moving table (also called a slider) 11t on whose upper surface the holding member 11h is installed.
• the rail 11r is located on the upper surface 10a of the device table 10 and extends along the depth direction.
• the holding member 11h supports and holds the imaging device 7. With the holding member 11h holding the imaging device 7, the moving table 11t can move along the depth direction on the rail 11r.
• the movement of the moving table 11t along the depth direction may be controlled by the control unit 8.
• the measurement system 1 may include a first rotation device 12 that rotates the imaging device 7 around a first rotation axis RA1.
• the first rotation axis RA1 may be parallel to a direction (e.g., X-axis direction) perpendicular to a predetermined direction (e.g., Y-axis direction) in which the imaging portions F3, F4, and F5 are arranged in the imaging plane Rp.
• the first rotation axis RA1 may be a rotation axis passing through the imaging device 7.
• the first rotation device 12 is configured to rotate the imaging device 7 in units of a predetermined angle ⁇ .
• the predetermined angle ⁇ may be, for example, about 0.1° to 2.0°, or about 0.5° to 1°.
• the first rotation device 12 may be provided in the moving device 11.
• the first rotation device 12 may be installed between the moving table 11t and the holding member 11h.
• the first rotation device 12 may rotate the holding member 11h of the moving device 11 and the imaging device 7 held by the holding member about the first rotation axis RA1.
• the first rotation device 12 may rotate only the imaging device 7 about the first rotation axis RA1 without rotating the holding member 11h of the moving device 11.
• the rotation of the imaging device 7 about the first rotation axis RA1 is controlled by the control unit 8.
• the first rotation device 12 may be a manual rotation device equipped with a stepping motor device, a linear motor device, an ultrasonic motor device, a manually rotated knob, a rotation adjustment device such as a screw, or the like.
• the aerial image display device 2 may include a second rotation device 13 located within the housing 6 for rotating the entire component 2a around the second rotation axis RA2.
• the second rotation axis RA2 may be parallel to a direction (e.g., the X-axis direction) perpendicular to a predetermined direction in which the imaging portions F3, F4, and F5 are aligned within the imaging plane Rp.
• the second rotation device 13 may rotate only the entire component 2a around the second rotation axis RA2 without rotating the housing 6.
• the rotation of the aerial image display device 2 or the entire component 2a around the second rotation axis RA2 is controlled by the control unit 8.
• the imaging direction 7d of the imaging device 7 may be the optical axis direction (also called the central axis direction) of the objective lens of the camera, or may be a direction perpendicular to the imaging surface of a CCD imaging element or the like.
• the imaging direction 7d of the imaging device 7 may be assumed to be the line of sight of the eye 20e of the user 20 facing the aerial image display device 2.
• the aerial image display device 2 faces the imaging device 7. Then, if the actual optical axis direction Da of the aerial image 9 does not coincide with the imaging direction 7d of the imaging device 7 (if the actual optical axis direction Da is misaligned with the imaging direction 7d), the amount of misalignment between the optical axis direction Da and the imaging direction 7d can be measured by a method (defocus method) of translating the imaging device 7 forward and backward in the depth direction, which will be described later, and the optical axis direction Da can be measured. In addition, by rotating the imaging device 7 around the first rotation axis RA1 to align the imaging direction 7d with the optical axis direction Da, the optical axis direction Da can be measured and the aerial image display device 2 can be accurately faced toward the imaging device 7.
• a method defocus method
• the positional deviation between the actual optical axis direction Da and the imaging direction 7d may exist only in the height direction (X-axis direction), only in the width direction (Y-axis direction), or in both the height direction (X-axis direction) and the width direction (Y-axis direction). In each case, the positional deviation can be measured and adjustments can be made to eliminate the positional deviation.
• the aerial image display device 2 When measuring whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad (see Figures 1 and 2) of the aerial image display device 2, the aerial image display device 2 is accurately positioned at a predetermined position directly facing the imaging device 7.
• the aerial image display device 2 may be positioned so that the image light emission section 6a of the aerial image display device 2 is perpendicular to the imaging direction 7d of the imaging device 7.
• the imaging direction 7d is a predetermined imaging direction 7da (imaging direction 7da that coincides with the design optical axis direction Dad).
• the amount of misalignment between the optical axis direction Da and the imaging direction 7da is not measured, and if there is an optical axis misalignment between the actual optical axis direction Da and the design optical axis direction Dad, the amount of misalignment between the optical axis direction Da and the imaging direction 7da is measured by a method (defocus method) of moving the imaging device 7 back and forth in the depth direction in parallel, which will be described later.
• the optical axis direction Da and the design optical axis direction Dad may be aligned by adjusting the arrangement of the components 2a of the aerial image display device 2, replacing the components 2a, etc.
• the optical axis misalignment between the actual optical axis direction Da and the design optical axis direction Dad may exist only in the height direction (X-axis direction), only in the width direction (Y-axis direction), or in both the height direction (X-axis direction) and the width direction (Y-axis direction).
• the position misalignment can be measured and adjustments can be made to eliminate the position misalignment.
• the measurement system 1 which measures the agreement or mismatch between the actual optical axis direction Da of the aerial image 9 and the design optical axis direction Dad in a plane perpendicular to the height direction (X-axis direction) based on the image data of the captured images P3 to P5, but is not limited to this.
• the control unit 8 acquires image data of the plurality of captured images P3 to P5 from the imaging device 7.
• the control unit 8 calculates luminance distribution waveforms LSF3 to LSF5 as shown in FIG. 10 based on the image data of the plurality of captured images P3 to P5.
• the control unit 8 calculates the characteristic values V3, V4, and V5 of the line spread functions LSF3 to LSF5.
• the characteristic values V1 to V7 refer to the characteristic values of the line spread functions LSF1 to LSF7, respectively.
• the characteristic value may be the peak value H of the line spread function, the half-width W of the line spread function, or the ratio of the half-width W to the quarter-width Q of the line spread function (hereinafter also referred to as the width ratio W/Q) (see FIG. 10).
• the peak value H is the maximum value of the line spread function. For example, the larger the peak value H of the line spread function LSF4 is (in the case of FIG.
• the half-width W is the width of the line spread function having a brightness of approximately 50% of the peak value H, and is expressed in units of the number of pixels.
• the smaller the half-width W of the line spread function LSF4 the closer the distance between the imaging portion F4 and the imaging device 7 is to the focal length of the imaging device 7.
• the same is true for the half-width W of the line spread functions LSF3 and LSF5.
• the smaller the half-width W of the line spread function LSF4 the higher the resolution (contrast value) of the aerial image R is.
• the quarter-value width Q is the width of the line spread function having a brightness of approximately 25% of the peak value H, and is expressed in units of the number of pixels.
• W/Q the closer to 1
• the larger the width ratio W/Q the higher the resolution (contrast value) of the aerial image R can be determined.
• the characteristic value may be a combination value obtained from the peak value H and the half-width W.
• the combination value may be a value obtained by dividing the peak value H by the half-width W, or may be some other value.
• the characteristic value is a combination value obtained by dividing the peak value H by the half-width W, it can be determined that the distance between the imaging portion F4 and the imaging device 7 is closer to the focal length of the imaging device 7 as the combination value of the line spread function LSF4 is larger.
• the resolution (contrast value) of the aerial image R is higher as the combination value of the line spread function LSF4 is larger.
• the control unit 8 may calculate multiple differences between the multiple characteristic values V3 to V5 (i.e., V3-V4, V3-V5, and V4-V5), and if all of the absolute values of the multiple differences are equal to or less than the threshold value T1, may determine that the actual optical axis direction Da of the aerial image 9 coincides with the depth direction (i.e., the design optical axis direction Dad). If at least one of the absolute values of the multiple differences exceeds the threshold value T1, the control unit 8 may determine that the optical axis direction Da of the aerial image 9 does not coincide with the depth direction.
• the threshold value T1 may be set appropriately based on the required specifications of the aerial image display device 2.
• control unit 8 may determine that the optical axis direction of the aerial image 9 coincides with the depth direction when the absolute value of the difference between the multiple characteristic values V3 to V5 is equal to or less than a threshold value T1.
• the control unit 8 may determine that the optical axis direction Da of the aerial image 9 coincides with the depth direction when all of the characteristic values V3 to V5 are equal to or greater than the threshold value T2.
• the control unit 8 may determine that the optical axis direction Da of the aerial image 9 does not coincide with the depth direction when at least one of the characteristic values V3 to V5 is less than the threshold value T2.
• the threshold value T2 may be set appropriately based on the required specifications of the aerial image display device 2.
• the control unit 8 may determine that the optical axis direction Da of the aerial image R coincides with the depth direction when all of the characteristic values V3 to V5 are equal to or less than the threshold value T3.
• the control unit 8 may determine that the optical axis direction Da of the aerial image 9 does not coincide with the depth direction when at least one of the characteristic values V3 to V5 exceeds the threshold value T3.
• the threshold value T3 may be set appropriately based on the required specifications of the aerial image display device 2, etc.
• the measurement system 1 can systematically measure whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad based on the characteristic values V3 to V5 of the line spread functions LSF3 to LSF5. Therefore, the measurement system 1 makes it possible to calibrate the optical axis direction Da of the aerial image R formed by the aerial image display device 2. That is, in order to match the actual optical axis direction Da with the design optical axis direction Dad, measures such as adjusting the arrangement of at least some of the components 2a of the aerial image display device 2 or replacing at least some of the components 2a can be adopted.
• the measurement system 1 can determine whether the actual optical axis direction Da of the aerial image 9 coincides with the imaging direction 7d and whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad based on the area of the modulation transfer function (see FIG. 3).
• the operation of the measurement system 1 that determines whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad based on the area of the modulation transfer function will be described.
• the optical axis direction measurement method based on the area of the modulation transfer function (hereinafter also referred to as the MTF area) is also referred to as the MTF area method.
• the control unit 8 calculates modulation transfer functions MTF3 to MTF5 by Fourier transforming each of the line spread functions LSF3 to LSF5 calculated from the captured images P3 to P5, as expressed in equation (3). Furthermore, the control unit 8 integrates each of the modulation transfer functions MTF3 to MTF5 on the spatial frequency axis, as expressed in equation (4), to measure the MTF areas A3 to A5. Note that the modulation transfer functions MTF3 to MTF5 do not have to be calculated by Fourier transforming the line spread functions LSF3 to LSF5.
• the modulation transfer functions MTF3 to MTF5 may be calculated directly from the image data of the captured images P3 to P5 using the chart method.
• the control unit 8 may calculate multiple differences between the multiple MTF areas A3 to A5 (i.e., A3-A4, A3-A5, and A4-A5), and if all of the absolute values of the multiple differences are equal to or less than the threshold value T4, may determine that the actual optical axis direction Da of the aerial image 9 coincides with the depth direction (design optical axis direction Dad). If at least one of the absolute values of the multiple differences exceeds the threshold value T4, the control unit 8 may determine that the optical axis direction of the aerial image 9 does not coincide with the depth direction.
• the threshold value T4 may be set appropriately based on the required specifications of the aerial image display device 2.
• the control unit 8 may determine that the actual optical axis direction Da of the aerial image 9 coincides with the depth direction when all of the MTF areas A3 to A5 are equal to or greater than the threshold value T5.
• the control unit 8 may determine that the actual optical axis direction Da of the aerial image 9 does not coincide with the depth direction when at least one of the MTF areas A3 to A5 is less than the threshold value T5.
• the threshold value T5 may be set appropriately based on the required specifications of the aerial image display device 2.
• the measurement system 1 can systematically measure whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad based on the MTF areas A3 to A5. Because the area of the modulation transfer function MTF is not easily affected by external light, etc., it is possible to accurately measure whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad by using the MTF areas A3 to A5. Therefore, the measurement system 1 makes it possible to accurately calibrate the actual optical axis direction Da of the aerial image R formed by the aerial image display device 2.
• the control unit 8 determines that the actual optical axis direction Da of the aerial image 9 does not match the design optical axis direction (depth direction) Dad, it may measure the optical axis shift of the actual optical axis direction Da of the aerial image 9 from the design optical axis direction Dad.
• the control unit 8 may measure the optical axis shift of the actual optical axis direction Da of the aerial image 9 from the design optical axis direction Dad without determining whether the actual optical axis direction Da of the aerial image 9 matches the design optical axis direction Dad.
• the control unit 8 controls the moving device 11 to move the imaging device 7 along the imaging direction (Z-axis direction) 7d as shown in FIG. 13, and position the imaging device 7 at multiple positions with different coordinates (Z coordinates) in the imaging direction 7d.
• Z0 is the initial coordinate of the imaging device 7 in the imaging direction 7d, and is the Z coordinate of the imaging device 7 when the distance between the imaging device 7 and the aerial image 9 becomes the initial setting distance.
• ⁇ Z may be, for example, about 0.1 mm to 5 mm, or about 0.2 mm to 2 mm.
• j is an integer in the range of -m1 ⁇ j ⁇ m2 (m1 and m2 are natural numbers).
• m1 and m2 may be, for example, natural numbers from 1 to 20, but are not limited to natural numbers from 1 to 20.
• the control unit 8 controls the imaging device 7 to capture an aerial image 9 in the imaging direction 7d from each position represented by Z coordinate Zj (-m1 ⁇ j ⁇ m2).
• FIG. 14 shows an example of an aerial image 9 captured by the imaging device 7 located at a position where the Z coordinate is Z0
• FIG. 15 shows an example of an aerial image 9 captured by the imaging device 7 located at a position where the Z coordinate is Zja (ja is a positive integer)
• FIG. 16 shows an example of an aerial image 9 captured by the imaging device 7 located at a position where the Z coordinate is Zjb (jb is a negative integer). Since the focal length of the imaging device 7 is fixed to the initial setting distance, it can be seen that the blur of the imaging parts F3, F4, and F5 changes as the imaging device 7 moves.
• the imaging device 7 outputs image data of (m1+m2+1) captured images P3 to P5 for each of the imaging parts F3 to F5 to the control unit 8.
• the control unit 8 acquires image data of (m1+m2+1) captured images P3-P5 from the imaging device 7 for each of the imaging regions F3-F5.
• the control unit 8 may acquire image data from the imaging device 7 via the acquisition unit 14.
• the control unit 8 calculates (m1+m2+1) line spread functions LSF3, LSF4, and LSF5 for each of the imaging portions F3 to F5 based on the image data of the (m1+m2+1) captured images P3 to P5, and calculates (m1+m2+1) characteristic values V3 to V5.
• the characteristic values V3 to V5 are the peak values H of the line spread functions LSF3 to LSF5, or a combination value obtained by dividing the peak value H by the half-width W.
• the control unit 8 calculates the maximum value VMAX of the (m1+m2+1) characteristic values V3 to V5 for each of the imaging portions F3 to F5, and calculates the Z coordinate (hereinafter also referred to as the focusing position) of the imaging device 7 when the characteristic values V3 to V5 become the maximum value VMAX .
• FIG. 17 is a graph showing the focusing positions FP3 to FP5 of the imaging parts F3 to F5.
• the focusing positions FP1 to FP7 respectively refer to the focusing positions when the characteristic values V1 to V7 are the maximum value VMAX .
• FIG. 17 also shows the focusing positions FP1, FP2, FP6, and FP7 of the imaging parts F1, F2, F6, and F7.
• the focusing positions FP1, FP2, FP6, and FP7 can be calculated in the same manner as the focusing positions FP3 to FP5.
• the focusing positions FP3 to FP5 of the imaging parts F3 to F5 are shown with the focusing position FP4 of the imaging part F4 as the reference position (0 mm).
• FIG. 17 shows the focusing positions FP3 to FP5 of the imaging parts F3 to F5 when the optical axis deviation occurs.
• the sign of the focal position FP3 (+1.0 mm) of the imaging part F3 is different from the sign of the focal position FP5 (-0.8 mm) of the imaging part F5.
• the control unit 8 determines that the optical axis of the aerial image 9 is deviated from the depth direction by an angle ⁇ that satisfies the following formula (5).
• is the absolute value of the in-focus position FP3
• is the absolute value of the in-focus position FP5 (see FIG. 17).
• L is the designed length of the aerial image 9 in the width direction (Y-axis direction).
• control unit 8 determines that the optical axis direction Da of the aerial image 9 is deviated from the design optical axis direction (depth direction) Dad by an angle ⁇ , it controls the second rotation device 13 (see Figures 1 and 2), which rotates the entire component 2a of the aerial image display device 2, to rotate the aerial image display device 2 by an angle ⁇ around the second rotation axis RA2.
• This makes it possible to calibrate the optical axis deviation of the aerial image R formed by the aerial image display device 2.
• the control unit 8 controls the second rotation device 13 to rotate the aerial image display device 2 by an angle ⁇ clockwise or counterclockwise when viewed from above the device stand 10.
• the control unit 8 may determine the direction in which to rotate the aerial image display device 2 based on the signs of the focus positions FP3 and FP5 so that the optical axis direction Da of the aerial image 9 is parallel to (i.e., coincides with) the design optical axis direction Dad.
• the second rotation device 13 may be a manual rotation device equipped with a stepping motor device, a linear motor device, an ultrasonic motor device, a manually rotated knob, a rotation adjustment device such as a screw, etc.
• Figure 19 shows focus positions FP3 to FP5 of imaging portions F3 to F5 when no optical axis misalignment occurs.
• Figure 19 also shows focus positions FP1, FP2, FP6, and FP7 of imaging portions F1, F2, F6, and F7.
• Focus positions FP1, FP2, FP6, and FP7 can be calculated in the same way as focus positions FP3 to FP5.
• the sign of focus position FP3 (-0.6 mm) of imaging portion F3 and the sign of focus position FP5 (-0.6 mm) of imaging portion F5 are the same, which indicates that no optical axis misalignment occurs (or the optical axis misalignment is reduced), as shown in Figure 20.
• the control unit 8 determines that the actual optical axis direction Da of the aerial image 9 does not deviate from the designed optical axis direction (depth direction) Dad, and does not need to rotate the component 2a of the aerial image display device 2.
• the above-described operation of the measurement system 1 is an operation in the case where the peak value H or a combination value obtained by dividing the peak value H by the half-width W is used as the characteristic values V3 to V5 of the line spread functions LSF3 to LSF5.
• the control unit 8 calculates the minimum value V MIN of the (m1+m2+1) characteristic values V3 to V5 for each of the imaging portions F3 to F5, and sets the Z coordinate of the imaging device 7 when the characteristic values V3 to V5 become the minimum value V MIN as the focusing positions FP3 to FP5.
• the minimum value V MIN may be the same as the threshold value T1.
• the measurement system 1 can systematically measure the optical axis deviation between the actual optical axis direction Da of the aerial image 9 and the design optical axis direction Dad based on the characteristic values V3 to V5 of the line spread functions LSF3 to LSF5. Therefore, the measurement system 1 makes it possible to calibrate the optical axis direction Da of the aerial image R formed by the aerial image display device 2.
• optical axis shift shift between the optical axis direction Da and the design optical axis direction Dad
• the control unit 8 calculates (m1+m2+1) modulation transfer functions MTF3-MTF5 for each of the imaging portions F3-F5 based on the image data of the (m1+m2+1) captured images P3-P5, and measures (m1+m2+1) MTF areas A3-A5.
• the control unit 8 calculates the maximum value AMAX of the (m1+m2+1) MTF areas A3-A5 for each of the imaging portions F3-F5, and calculates the Z coordinate (focus position FP3-FP5) of the imaging device 7 where the MTF areas A3-A5 are maximum value AMAX .
• the control unit 8 can measure the optical axis shift (tilt angle ⁇ ) of the aerial image 9 based on the focusing positions FP3 to FP5 at which the MTF areas A3 to A5 reach their maximum value A MAX , and calibrate the optical axis shift of the aerial image R formed by the aerial image display device 2.
• the operation of the measurement system 1 that measures the optical axis shift of the aerial image 9 based on the MTF areas A3 to A5 and calibrates the optical axis shift of the aerial image is similar to the operation of the measurement system 1 that measures the optical axis shift of the aerial image 9 based on the characteristic values V3 to V5 and calibrates the optical axis shift of the aerial image, and therefore a detailed description thereof will be omitted.
• the control unit 8 may calculate (m1+m2+1) line spread functions LSF3-LSF5 for each imaging portion F3-F5 based on the image data of the (m1+m2+1) captured images P3-P5, and calculate (m1+m2+1) modulation transfer functions MTF3-MTF5 by Fourier transforming the (m1+m2+1) line spread functions LSF3-LSF5.
• the control unit 8 may calculate (m1+m2+1) modulation transfer functions MTF3-MTF5 for each imaging portion F3-F5 based on the image data of the (m1+m2+1) captured images P3-P5 using the chart method.
• the measurement system 1 performs a defocus operation on the imaging device 7, and can systematically measure the optical axis deviation between the optical axis direction of the aerial image 9 and the design optical axis direction based on the change in the MTF areas A3 to A5 accompanying the movement of the imaging device 7.
• the defocus operation is an operation that changes the degree of focus (degree of focus, degree of blur of the captured image) of each imaging part of the aerial image 9 by moving the imaging device 7 back and forth in the imaging direction 7d, as shown in FIG. 13. Since the area of the modulation transfer function MTF is not easily affected by external light, etc., it is possible to accurately measure whether the actual optical axis direction Da of the aerial image 9 coincides with the design optical axis direction Dad by using the MTF areas A3 to A5. Therefore, the measurement system 1 makes it possible to accurately calibrate the actual optical axis direction Da of the aerial image R formed by the aerial image display device 2.
• the control unit 8 controls the first rotation device 12 to rotate the imaging device 7 around the first rotation axis RA1 as shown in FIG. 21, and captures the aerial image 9 in a plurality of imaging directions 7d that have different angles with the depth direction (Z-axis direction).
• the plurality of imaging directions 7d are directions that form an angle collectively represented by ⁇ k with the depth direction (design optical axis direction Dad). ⁇ k is also referred to as the imaging angle.
• ⁇ may be, for example, about 0.1° to 2°, or about 0.5° to 1°.
• k is an integer in the range of -n1 ⁇ k ⁇ n2 (n1, n2 are natural numbers).
• n1 and n2 may be, for example, a natural number between 1 and 20, but is not limited to a natural number between 1 and 20.
• Fig. 21 shows a case where the rotation angle of the imaging device 7 is ⁇ ka (ka is a positive integer) and a case where the rotation angle of the imaging device 7 is ⁇ kb (kb is a negative integer).
• the control unit 8 controls the imaging device 7 to capture an aerial image 9 in each direction represented by an imaging angle ⁇ k (-n1 ⁇ k ⁇ n2).
• the imaging device 7 outputs image data of (n1+n2+1) captured images P3-P5 for each imaging portion F3-F5 to the control unit 8.
• the control unit 8 acquires image data of (n1+n2+1) captured images P3-P5 from the imaging device 7 for each imaging portion F3-F5.
• the control unit 8 may acquire image data from the imaging device 7 via the acquisition unit 14.
• the control unit 8 calculates (n1+n2+1) line spread functions LSF3 to LSF5 based on the image data of the (n1+n2+1) captured images P3 to P5, and calculates (n1+n2+1) characteristic values V3 to V5.
• the characteristic values V3 to V5 may be the peak value H or the half width W of the line spread functions LSF3 to LSF5.
• the characteristic values V3 to V5 may be a combination value obtained by dividing the peak value H by the half width W.
• the control unit 8 calculates multiple differences between the multiple characteristic values V3 to V5 for each imaging angle ⁇ k (i.e., V3-V4, V3-V5, and V4-V5), and when the absolute value of the multiple differences at a certain imaging angle ⁇ 1 is equal to or less than a threshold value T6, it may determine that the actual optical axis direction Da of the aerial image 9 is inclined at the inclination angle ⁇ 1 with respect to the depth direction (design optical axis direction Dad).
• the threshold value T6 may be set appropriately based on the required specifications of the aerial image display device 2.
• the control unit 8 may determine that the actual optical axis direction Da of the aerial image is inclined by the inclination angle ⁇ 2 with respect to the design optical axis direction Dad when all of the characteristic values V3 to V5 are equal to or greater than the threshold value T7 at a certain imaging angle ⁇ 2.
• the threshold value T7 may be set appropriately based on the required specifications of the aerial image display device 2.
• the control unit 8 may determine that the actual optical axis direction Da of the aerial image is inclined by the inclination angle ⁇ 3 with respect to the design optical axis direction Dad when all of the characteristic values V3 to V5 are equal to or smaller than the threshold value T8 at a certain imaging angle ⁇ 3.
• the threshold value T8 may be set appropriately based on the required specifications of the aerial image display device 2.
• control unit 8 determines that the actual optical axis direction Da of the aerial image 9 is deviated from the design optical axis direction (depth direction) Dad by the inclination angles ⁇ 1, ⁇ 2, and ⁇ 3, the control unit 8 controls the second rotation device 13 to rotate the aerial image display device 2 by a rotation angle equal to the inclination angles ⁇ 1, ⁇ 2, and ⁇ 3 around the second rotation axis RA2.
• This makes it possible to calibrate the optical axis shift of the aerial image R formed by the aerial image display device 2.
• the control unit 8 controls the second rotation device 13 to rotate the aerial image display device 2 clockwise or counterclockwise by a rotation angle equal to the inclination angles ⁇ 1, ⁇ 2, and ⁇ 3 when viewed from above the device stand 10.
• the control unit 8 may determine the direction in which to rotate the aerial image display device 2 so that the optical axis shift of the aerial image 9 is eliminated.
• the measurement system 1 can systematically measure the optical axis deviation between the actual optical axis direction Da of the aerial image 9 and the design optical axis direction Dad based on the changes in the characteristic values V3 to V5 that accompany the rotation of the imaging device 7. Therefore, the measurement system 1 makes it possible to calibrate the optical axis direction Da of the aerial image R formed by the aerial image display device 2.
• the control unit 8 calculates (n1+n2+1) modulation transfer functions MTF for each of the imaging portions F3 to F5 based on the image data of the (n1+n2+1) captured images P3 to P5, and measures (n1+n2+1) MTF areas A3 to A5.
• the control unit 8 calculates multiple differences between the multiple MTF areas A3 to A5 (i.e., A3-A4, A3-A5, and A4-A5) for each imaging angle ⁇ k, and if the absolute value of the multiple differences at a certain imaging angle ⁇ 4 is equal to or less than a threshold value T9, it may determine that the actual optical axis direction Da of the aerial image 9 is inclined by the inclination angle ⁇ 4 with respect to the depth direction (design optical axis direction Dad).
• the threshold value T9 may be set appropriately based on the required specifications of the aerial image display device 2.
• the control unit 8 may determine that the actual optical axis direction Da of the aerial image is inclined by the inclination angle ⁇ 5 with respect to the design optical axis direction Dad when all of the MTF areas A3 to A5 are equal to or greater than the threshold value T10 at a certain imaging angle ⁇ 5.
• the threshold value T10 may be set appropriately based on the required specifications of the aerial image display device 2.
• the control unit 8 may calculate (n1+n2+1) line spread functions LSF3-LSF5 for each imaging region F3-F5 based on the image data of the (n1+n2+1) captured images P3-P5, and calculate (n1+n2+1) modulation transfer functions MTF3-MTF5 by Fourier transforming the (n1+n2+1) line spread functions LSF3-LSF5.
• the control unit 8 may calculate (n1+n2+1) modulation transfer functions MTF3-MTF5 for each imaging region F3-F5 based on the image data of the (n1+n2+1) captured images P3-P5 using the chart method.
• the measurement system 1 can systematically measure the optical axis misalignment between the actual optical axis direction Da of the aerial image 9 and the design optical axis direction Dad based on the MTF areas A3 to A5. Because the area of the modulation transfer function MTF is not easily affected by external light, etc., it is possible to accurately measure whether the actual optical axis direction Da of the aerial image 9 matches the design optical axis direction Dad by using the MTF areas A3 to A5. Therefore, the measurement system 1 makes it possible to accurately calibrate the optical axis direction Da of the aerial image R formed by the aerial image display device 2.
• the above describes the operation of the measurement system 1, which measures the optical axis shift around the height direction (X-axis direction) perpendicular to the width direction (Y-axis direction) based on multiple captured images P3 to P5 captured from multiple imaging sites F3 to F5 aligned in the width direction (Y-axis direction) in the imaging plane Rp of the aerial image 9, and calibrates the optical axis shift, but is not limited to this.
• the measurement system 1 can also measure the optical axis shift around the width direction (Y-axis direction) perpendicular to the height direction (X-axis direction) based on multiple captured images (e.g., multiple captured images P1, P3, P6 or multiple captured images P2, P5, P7) captured from multiple imaging sites (e.g., multiple imaging sites F1, F3, F6 or multiple imaging sites F2, F5, F7) aligned in the height direction (X-axis direction) in the imaging plane Rp of the aerial image 9, and calibrate the optical axis shift.
• multiple captured images e.g., multiple captured images P1, P3, P6 or multiple captured images P2, P5, P7
• multiple imaging sites e.g., multiple imaging sites F1, F3, F6 or multiple imaging sites F2, F5, F7 aligned in the height direction (X-axis direction) in the imaging plane Rp of the aerial image 9, and calibrate the optical axis shift.
• the measurement system 1 can measure the optical axis shift in the height direction (X-axis direction) and the optical axis shift in the width direction (Y-axis direction) based on a plurality of captured images of a plurality of captured portions F1 to F7 in the imaging plane Rp of the aerial image 9, and can also calibrate these optical axis shifts.
• the line spread functions LSF1, LSF2, LSF6, and LSF7 can be calculated in the same manner as the line spread functions LSF3 to LSF5.
• the characteristic values V1, V2, V6, and V7 can be calculated in the same manner as the characteristic values V3, V4, and V5.
• the modulation transfer functions MTF1, MTF2, MTF6, and MTF7 can be calculated in the same manner as the modulation transfer functions MTF3, MTF4, and MTF5.
• the MTF areas A1, A2, A6, and A7 can be measured in the same manner as the MTF areas A3 to A5.
• the optical axis shift is measured using the measurement system 1, and if an optical axis shift is present, the optical axis shift is calibrated, allowing the modulation transfer functions MTF1 to MTF7 to be calculated with high accuracy. As a result, degradation of the resolution of the aerial image display device 2 can be suppressed.
• This disclosure can be implemented in the following configurations (1) to (15).
• An aerial image display device including a display unit and an optical system that forms an image light emitted from the display unit into a real aerial image
• An aerial image display device wherein when S1 is the area obtained by integrating a first modulation transfer function of an aerial image formed by the optical system on a spatial frequency axis, the optical system is an ideal optical system having a diffraction-limited resolution, and S2 is the area obtained by integrating a second modulation transfer function of an ideal aerial image formed by the ideal optical system on a spatial frequency axis, the ratio S1/S2 of area S1 to area S2 is 0.58 or greater.
• An aerial image display device according to any one of the above configurations (1) to (4), in which the distortion of the aerial image is 5% or less.
• An aerial image display device in which the distortion of the aerial image is defined by the distortion of a corner when the corner of the aerial image located at the end of an ideal rectangular aerial image is used as a reference and the deviation length from the edge, expressed as a percentage, of the corner is defined as the distortion of the corner.
• An aerial image display device in which the distortion of the aerial image is a distortion of the four corners.
• An aerial image display device according to the above configuration (6) or (7), in which the distortion of the aerial image is greatest at the four corners.
• the optical system includes: a first concave mirror that reflects the image light emitted from the display unit in a direction different from a direction toward the display unit; a convex mirror that reflects the image light reflected by the first concave mirror in a direction different from a direction toward the first concave mirror; a second concave mirror that reflects the image light reflected by the convex mirror in a direction different from the direction toward the convex mirror, and forms a real aerial image;
• the aerial image display device according to any one of the above configurations (1) to (9), comprising:
• the first concave mirror and the second concave mirror are free-form concave mirrors,
• the first concave mirror and the second concave mirror face each other in a tilted state
• the optical system comprises: a first concave mirror that reflects the image light emitted from the display unit in a direction different from a direction toward the display unit; a second concave mirror that reflects the image light reflected by the first concave mirror in a direction different from the direction toward the first concave mirror, and forms a real aerial image;
• the aerial image display device according to any one of the above configurations (1) to (9), comprising:
• the curvature of the first concave mirror is greater than the curvature of the second concave mirror, the first concave mirror and the second concave mirror face each other in a tilted state,
• the aerial image display device according to the above configuration (13) or (14), wherein the display unit is located between the first concave mirror and the second concave mirror.
• the aerial image display device disclosed herein can suppress a decrease in the resolution of the aerial image. Furthermore, the aerial image display device disclosed herein can reduce distortion of the aerial image and suppress a decrease in the brightness of the aerial image.

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• 2024
  • 2024-06-11 JP JP2025527945A patent/JPWO2024257770A1/ja active Pending
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