Display apparatus capable of multi-depth expression

Provided is a display apparatus including an image forming device configured to form an image, an optical system configured to provide an output image by combining light containing an outside landscape with the image formed by the image forming device, and a driving device configured to adjust a distance between the image forming device and the optical system, wherein the driving device includes a fixed frame, a movable frame which faces the fixed frame and is movable, an actuator configured to change a distance between the fixed frame and the movable frame, and a fixing member configured to fix the distance between the fixed frame and the movable frame, wherein the image forming device is fixed to the movable frame.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No. 10-2019-0138196, filed on Oct. 31, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Example embodiments of the present disclosure relate to a display apparatus capable of multi-depth expression, and more particularly, to a display apparatus capable of multi-depth expression and configured to reduce power consumption in a depth maintaining state.

2. Description of Related Art

3D image display technology has been used in various fields, and recently, the application of 3D image display technology has also been extended to image devices related to virtual reality (VR) displays and augmented reality (AR) displays.

Head mounted displays providing VR have been commercially available and widely used in the entertainment industry. In addition, head mounted displays have been developed into types applicable to the fields of medicine, education, and other industries.

AR displays, an advanced form of VR displays, are image devices combining the real world with VR and capable of bringing out interactions between reality and VR. The interaction between reality and VR is based on the function of providing real-time information about real situations, and the effect of reality is further increased by overlaying virtual objects or information on a real-world environment.

In these devices, a stereoscopy technique is commonly used for displaying three-dimensional (3D) images, and in this case, the alignment of a display with an optical system may be a problem in a process of changing the distance between the display and the optical system for multi-depth expression. Accordingly, there are attempts to find a 3D image display method for more precise alignment between a display and an optical system.

SUMMARY

One or more example embodiments provide display apparatuses capable of multi-depth expression and having an actuator structure for reducing power consumption in a depth maintaining state.

According to an aspect of an example embodiment, there is provided a display apparatus including an image forming device configured to form an image, an optical system configured to provide an output image by combining light containing an outside landscape with the image formed by the image forming device, and a driving device configured to adjust a distance between the image forming device and the optical system, wherein the driving device includes a fixed frame, a movable frame which faces the fixed frame and is movable, an actuator configured to change a distance between the fixed frame and the movable frame, and a fixing member configured to fix the distance between the fixed frame and the movable frame, wherein the image forming device is fixed to the movable frame.

The actuator may include a first elastic bridge having a curved surface which is convex toward the fixed frame, a second elastic bridge having a curved surface which is convex toward the movable frame, and a variable length element fixed between both ends of the first elastic bridge and both ends of the second elastic bridge, and respectively having a length that is variable.

The variable length element may include a shape memory alloy or an electroactive polymer, and the length of the variable length element may change based on an electrical control.

The first elastic bridge may have elastic restoring force in a direction in which a radius of curvature of the first elastic bridge increases, and a center portion of the first elastic bridge is fixed to the fixed frame.

The second elastic bridge may have elastic restoring force in a direction in which a radius of curvature of the second elastic bridge increases, and a center portion of the second elastic bridge is fixed to the movable frame.

The fixing member may include a pair of side frames respectively fixed to opposite side edges of the fixed frame.

The pair of side frames may extend from the fixed frame toward the movable frame, and the pair of side frames may have fixed ends fixed to the fixed frame and free ends which are opposite the fixed ends.

The pair of side frames may include a plurality of protrusions which protrude from surfaces of the free ends and are provided at different distances from the fixed frame, the plurality of protrusions being configured to contact with opposite sides of the movable frame and restrain movement of the movable frame.

The pair of side frames may be configured such that the free ends of the pair of side frames which face each other move away from each other while the distance between the fixed frame and the movable frame is changed and move closer to each other while the distance between the fixed frame and the movable frame is maintained.

The pair of side frames may include bimetal or piezoelectric elements which respectively bend or stretch based on a temperature control or an electrical control, and the pair of side frames may be bent while the distance between the fixed frame and the movable frame is changed, and may be stretched while the distance between the fixed frame and the movable frame is maintained.

The fixing member may further include variable length elements fixed between the fixed ends and the free ends and having variable lengths, the pair of side frames may have elastic restoring force in directions in which the free ends face each other, and the variable length elements fixed between the fixed ends and the free ends may be contracted based on the distance between the fixed frame and the movable frame being changed.

The fixing member may include a pair of first rods configured to rotate and provided at both side edges of the fixed frame, and a pair of second rods configured to rotate and provided at both side edges of the movable frame, wherein end portions of the pair of first rods and end portions of the pair of second rods corresponding to the end portions of the pair of first rods are configured to contact each other and interfere with each other.

The fixing member may be configured to be switched between a first state in which the pair of first rods and the pair of second rods corresponding to the pair of first rods are fixed in a straight line with each other and a second state in which the pair of first rods and the pair of second rods corresponding to the pair of first rods are fixed at an inclined angle with respect to each other.

The fixing member may be switched from the second state to the first state based on the distance between the fixed frame and the movable frame being increased, and is switched from the first state to the second state based on the distance between the fixed frame and the movable frame being decreased.

The end portions of the pair of first rods may include recesses and barriers surrounding the recesses, wherein a width of each of the end portions of the pair of second rods is less than a width of each of the recesses, and each of the end portions of the pair of second rods are provided in each of the recesses, and wherein the fixing member is configured such that the end portions of the pair of second rods are in contact with bottom surfaces of the recesses in the first state and are in contact with inner walls of the barriers in the second state.

The end portions of the pair of second rods may include recesses and barriers surrounding the recesses, wherein a width of each of the end portions of the pair of first rods is less than a width of each of the recesses and each of the end portions of the pair of first rods are provided in each of the recesses, and wherein the fixing member is configured such that the end portions of the pair of first rods are in contact with bottom surfaces of the recesses in the first state and are in contact with inner walls of the barriers in the second state.

The fixing member may further include variable length elements respectively connected between both side edges of the fixed frame and the end portions of the pair of first rods and respectively having a length that is variable, and the variable length elements respectively connected between both side edges of the fixed frame and the end portions of the pair of first rods may be contracted based on the fixing member being switched from the first state to the second state.

The fixing member may further include variable length elements respectively connected between both side edges of the movable frame and the end portions of the pair of second rods, and respectively having a length that is variable, and the variable length elements respectively connected between both side edges of the movable frame and the end portions of the pair of second rods may be contracted based on the fixing member being switched from the first state to the second state.

The end portions of the pair of first rods and the end portions of the pair of second rods corresponding to the end portions of the pair of first rods may have complementary shapes and are configured to be engaged with each other, wherein the fixing member may further include variable length elements respectively connected between both side edges of the movable frame and the end portions of the pair of second rods, and respectively having a length that is variable, and wherein the variable length elements respectively connected between both side edges of the movable frame and the end portions of the pair of second rods may be contracted based on the fixing member being switched from the first state to the second state.

The fixing member may include a pair of first rods configured to rotate and provided at both side edges of the fixed frame, and a pair of second rods configured to rotate and provided at both side edges of the movable frame, wherein end portions of the pair of first rods and end portions of the pair of second rods corresponding to the end portions of the pair of first rods are configured to contact each other and interfere with each other.

The actuator may include first variable length elements connected between the fixed frame and inner lateral surfaces of the pair of first rods, and respectively having a length that is variable, and second variable length elements connected between the fixed frame and outer lateral surfaces of the pair of first rods, and respectively having a length that is variable.

The fixing member may be configured to be switched between a first state in which the pair of first rods and the pair of second rods corresponding to the pair of first rods are fixed in a straight line with each other and a second state in which the pair of first rods and the pair of second rods corresponding to the pair of first rods are fixed at an inclined angle with respect to each other, wherein based on the distance between the fixed frame and the movable frame being increased, the first variable length elements are shortened and the second variable length elements are elongated to switch the fixing member from the second state to the first state, and based on the distance between the fixed frame and the movable frame being decreased, the first variable length elements are elongated and the second variable length elements are shortened to switch the fixing member from the first state to the second state.

The actuator may include first variable length elements connected between the movable frame and inner lateral surfaces of the pair of second rods, and respectively having a length that is variable, and second variable length elements connected between the movable frame and outer lateral surfaces of the pair of second rods, and respectively having a length that is variable.

The display apparatus may further include a processor configured to determine the distance between the image forming device and the optical system based on depth information of the image to be displayed and control the driving device.

The display apparatus may be a virtual reality (VR), augmented reality (AR), or mixed reality (MR) display apparatus which is implemented in a head mounted type apparatus, a glasses type apparatus, or a goggle type apparatus.

According to another aspect of an example embodiment, there is provided a display apparatus including an image forming device configured to form an image, an optical system configured to provide combine the image formed by the image forming device and light provided from an outside of the display apparatus, and a driving device configured to change a distance between the image forming device and the optical system, wherein the driving device includes a fixed frame, a movable frame which faces the fixed frame and is movable, an actuator configured to control a distance between the fixed frame and the movable frame based on a voltage applied, and a fixing member configured to fix the distance between the fixed frame and the movable frame.

The voltage may be applied while the distance between the fixed frame and the movable frame changes, and the voltage may not be applied while the distance between the fixed frame and the movable frame is maintained.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the example embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, the expression, “at least one of a, b, and c,” should be understood as including only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

Hereinafter, display apparatuses capable of multi-depth expression will be described with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements, and the sizes of elements may be exaggerated for clarity of illustration. Example embodiments described herein are for illustrative purposes only, and various modifications may be made therefrom. In the following description, when an element is referred to as being “above” or “on” another element in a layered structure, it may be directly on an upper, lower, left, or right side of the other element while making contact with the other element or may be above an upper, lower, left, or right side of the other element without making contact with the other element.

FIG. 1is a schematic view schematically illustrating a structure and operation of a display apparatus100according to an example embodiment. Referring toFIG. 1, the display apparatus100of the example embodiment may include an image forming device110configured to form images, a combiner member130, for example, a light system, an optical system, or an optical device, configured to provide images formed by the image forming device110together with light containing and propagating from an outside landscape, a driving device120configured to adjust the distance between the image forming device110and the combiner member130, and a processor140configured to control the image forming device110and the driving device120according to information about the depths of images to be displayed.

The image forming device110forms images by modulating light according to information on images to be provided to a viewer. Images formed by the image forming device110may be, for example, stereo images which are respectively provided to the left eye and the right eye of the viewer, holographic images, light field images, or integral photography (IP) images, and may include multi-view images or super multi-view images. In addition, images formed by the image forming device110may be general two-dimensional images, but embodiments are not limited thereto.

For example, the image forming device110may include a liquid crystal on silicon (LCoS) device, a liquid crystal display (LCD) device, an organic light emitting diode (OLED) display device, or a digital micromirror device (DMD). In addition, the image forming device110may include a next generation display device such as a micro LED display device or a quantum dot (QD) LED display device. When the image forming device110is a self-emissive display device such as an OLED display device or a micro LED, the image forming device110may include only one display panel. When the image forming device110is a non-emissive display device such as an LCoS device or an LCD device, the image forming device110may further include a light source configured to provide illumination light and a beam splitter configured to adjust the path of illumination light.

The combiner member130may change the path of an image formed by the image forming device110and output the image such that the image may have a size suitable for the viewer's field of view and may be delivered to a viewer's eye. The combiner member130may include a focusing optical system131and may also include a beam splitter132configured to change the path of light by splitting the light. The focusing optical system131may be an imaging member having refractive power and configured to enlarge or reduce images formed by the image forming device110. InFIG. 1, the focusing optical system131is illustrated as a concave mirror, but embodiments are not limited thereto. For example, the focusing optical system131may be provided as a combination of a convex lens, a concave lens, and the like.

The beam splitter132may be a half mirror that transmits a portion of incident light and reflects the other portion of the incident light. However, embodiments are not limited thereto. For example, the beam splitter132may be a polarization beam splitter that transmits or reflects incident light according to the polarization of the incident light. When the beam splitter132is a polarization beam splitter, additional optical elements for polarization conversion may be further included in the combiner member130.

As shown inFIG. 1, the combiner member130may have an integrated structure in which the focusing optical system131and the beam splitter132are fixed through a transparent light guide plate133. For example, the beam splitter132may be arranged in a diagonal direction inside the light guide plate133, and an end portion of the light guide plate133may have a convexly curved surface. A concave mirror may be formed on the end portion of the light guide plate133by coating the convexly curved surface of the light guide plate133with a reflective film. In this example embodiment, an image formed by the image forming device110enters the inside of the light guide plate133through a light entrance surface of the light guide plate133. Thereafter, the image may be transmitted through the beam splitter132, enlarged and reflected by the focusing optical system131, and then reflected by the beam splitter132onto the viewer's eye. However, this is an example, and the structure of the combiner member130is not limited thereto.

The combiner member130may not only transmit light L10containing an image formed by the image forming device110to the viewer's eye, but may also transmit light L20containing and propagating from a front outside landscape to the viewer's eye. For example, the light guide plate133and the beam splitter132of the combiner member130may be configured to transmit the light L20containing and propagating from the outside landscape. The light L20propagating from the outside does not contain an artificial image displayed by a separate display device, but contains an actual foreground existing in front of the viewer. Therefore, the viewer may simultaneously recognize the actual foreground and a virtual image which is artificially generated by the image forming device110. Therefore, the display apparatus100may function as a see-through-type display. In this regard, the display apparatus100of the example embodiment may be used for implementing augmented reality (AR) or mixed reality (MR). For example, the display apparatus100of the example embodiment may be a near-eye AR display apparatus.

The combiner member130is not limited to the illustrated shape and structure. Additional optical elements may be further provided to transmit an image formed by the image forming device110to a viewer's pupil together with a real-environment image of the front side of the viewer, and optical windows having various shapes and structures may be employed.

As described above, an image formed by the image forming device110reaches the viewer's eye along a propagating path in which the image is transmitted through the beam splitter132, reflected by the focusing optical system131, and then reflected by the beam splitter132. In the propagating path, the viewer recognizes a virtual image formed on a virtual image plane VP which is at a position in front of the viewer, and the depth of the virtual image, which the viewer recognizes, varies depending on the position of the virtual image plane VP.

The display apparatus100of the example embodiment may change the position of the virtual image plane VP to reflect the depth of the image to be displayed rather than fixing the position of the virtual image plane VP. To this end, the display apparatus100may include the driving device120configured to change the position of the image forming device110. The driving device120may move the image forming device110in parallel such that the distance between the image forming device110and the focusing optical system131of the combiner member130may change. Then, when the position of the image forming device110is changed in directions A1, the position of the virtual image plane VP may be changed in directions A2. For example, when the image forming device110is moved away from the focusing optical system131of the combiner member130, the depth of an image that the viewer feels may be increased by an amount from the virtual image plane VP to a virtual image plane VP′.

The processor140may generate a light modulation signal SG1and a driving signal SG2which are to be respectively transmitted to the image forming device110and the driving device120according to information about an image that the viewer will recognize. The image forming device110and the driving device120may be controlled respectively by the light modulation signal SG1and the driving signal SG2generated by the processor140. For example, the image forming device110forms an image based on the light modulation signal SG1provided from the processor140. In addition, the driving device120adjusts the position of the image forming device110based on the driving signal SG2provided from the processor140such that the virtual image plane VP may be positioned in accordance with the depth of the image formed by the image forming device110. To this end, the processor140may generate the driving signal SG2by determining the distance between the image forming device110and the combiner member130based on information about the depth of the image which is included in the light modulation signal SG1to be transmitted to the image forming device110.

Image information may include pixel-specific data, related to color values of a plurality of pixels, and depth information associated with the positions of the virtual image plane VP to which the images are respectively to be formed, for each of a plurality of frame images to be provided to the viewer. The processor140may generate, as the light modulation signal SG1, an electrical signal for implementing color values determined by referring to the pixel-specific data included in the image information. In addition, the processor140may generate the driving signal SG2to place the image forming device110such that the virtual image plane VP may be formed at a position corresponding to a representative depth value which is set with reference to the depth information. When the light modulation signal SG1and the driving signal SG2generated by the processor140are respectively transmitted to the image forming device110and the driving device120, the viewer may recognize an image from the position of the virtual image plane VP which corresponds to the depth of the image.

In addition, the driving signal SG2for driving the driving device120may be transmitted after a predetermined delay time from the transmission time of the light modulation signal SG1. For example, the predetermined delay time may be set to be greater than the convergence-accommodation time of the viewer's eye that is the time necessary for the human eye to perceive an image at a changed depth position.

The driving device120employed in the display apparatus100of the example embodiment may include a shape-variable material to widen the position driving range of the image forming device110while reducing the volume of the driving device120as much as possible. For example, the driving device120may move the image forming device110while being changed in shape according to a signal applied to the driving device120. For this variable shape, the driving device120may include a material of which the shape is changed in a certain condition. For example,FIGS. 2A and 2Bare views schematically illustrating a structure and operation of the driving device120according to an example embodiment.

Referring toFIG. 2A, the driving device120may include a fixed frame11which is fixed to the inside of the display apparatus100, a movable frame12which is arranged to face the fixed frame11and is movable, an actuator20which is configured to change the distanced between the fixed frame11and the movable frame12, and a fixing member30configured to fix the distance between the fixed frame11and the movable frame12. The fixed frame11and the movable frame12may have flat plate shapes which are parallel to each other. The movable frame12may be configured to be movable in a direction perpendicular to a surface facing the fixed frame11. In addition, the driving device120may further include a driving circuit for applying a driving voltage to the actuator20under the control of the processor140.

The image forming device110may be fixed to a lower surface of the movable frame12and may face the light entrance surface of the combiner member130. For example, the image forming device110may be a display panel of a self-emissive display device.

The actuator20may be configured to move the movable frame12to change the distance between the fixed frame11and the movable frame12. For example, the actuator20may include a first elastic bridge21having a curved surface which is convex toward the fixed frame11, a second elastic bridge22having a curved surface which is convex toward the movable frame12, and a variable length element23fixed between both ends of the first elastic bridge21and both ends of the second elastic bridge22and having a variable length.

The first elastic bridge21and the second elastic bridge22may include a plate-like elastic material such as a metal or plastic. Since both ends of the first elastic bridge21and both ends of the second elastic bridge22are fixed to the variable length element23which is shorter than the length of the first elastic bridge21and the length of the second elastic bridge22, respectively, the first elastic bridge21and the second elastic bridge22may be curved in an arch shape by the variable length element23. Therefore, each of the first elastic bridge21and the second elastic bridge22has elastic restoring force in a direction in which the radius of curvature thereof increases. A convex center portion of the first elastic bridge21may be fixed to a lower surface of the fixed frame11, for example, by using a fixing plate24. In addition, a convex center portion of the second elastic bridge22may be fixed to an upper surface of the movable frame12, for example, by using a fixing plate25. Then, when the first elastic bridge21and the second elastic bridge22are elastically deformed, the convex center portion of the first elastic bridge21may not move on the lower surface of the fixed frame11, and the convex center portion of the second elastic bridge22may not move on the upper surface of the movable frame12.

The variable length element23may be configured to be changed in length by electrical control. For example, the variable length element23may include a material such as a shape memory alloy (SMA) or an electroactive polymer which is deformable into a predetermined shape by a certain drive signal. The SMA may include, for example, a nickel-titanium (Ni—Ti) alloy, a copper-zinc (Cu—Zn) alloy, a gold-cadmium (Au—Cd) alloy, an indium-titanium (In—Ti) alloy, or the like. In this case, when a driving voltage is applied to the variable length element23, heat may be generated in the variable length element23, and the variable length element23may contract because of the heat. In addition, when the driving voltage is not applied to the variable length element23, the variable length element23may extend to its original length.

The fixing member30, which fixes the distance between the fixed frame11and the movable frame12while the movable frame12is not moving, may include, for example, a pair of side frames13arespectively fixed to both side edges of the fixed frame11. Each of the pair of side frames13amay include a plate-shaped elastic material extending in a direction from the fixed frame11toward the movable frame12. In addition, the pair of side frames13amay include fixed ends which are fixed to the fixed frame11and free ends which are opposite the fixed ends. The free ends of the pair of side frames13amay face both sides of the movable frame12.

In addition, the pair of side frames13amay include a plurality of first and second protrusions13band13cprotruding from surfaces of the free ends such that the first protrusion13band the second protrusion13cmay make contact with both sides of the movable frame12to restrain the movable frame12from moving. The first protrusion13band the second protrusion13cmay be located at different distances from the fixed frame11in the direction from the fixed frame11toward the movable frame12. For example, the first protrusions13bmay be arranged at a first distance from the fixed frame11, and the second protrusions13cmay be are arranged at a second distance from the fixed frame11which is greater than the first distance. Thus, when both sides of the movable frame12are in contact with the first protrusions13b, the movable frame12may be fixed at the first distance from the fixed frame11, and when both sides of the movable frame12are in contact with the second protrusions13c, the movable frame12may be fixed at the second distance from the fixed frame11.

In an initial state, the variable length element23may not be contracted. In addition, as shown inFIG. 2A, both sides of the movable frame12may be located between the first protrusions13band the second protrusions13c. The movable frame12may be forced to move toward the fixed frame11because of the elastic restoring force of the first elastic bridge21and the second elastic bridge22. Therefore, both sides of the movable frame12are brought into contact with the first protrusions13band are not further moved toward the fixed frame11because of the first protrusions13b, such that the position of the movable frame12is fixed. Then, the image forming device110fixed to the movable frame12is also fixed at a position relatively distant from the combiner member130.

When the driving device120applies a driving voltage to the variable length element23under the control of the processor140, the variable length element23contracts such that both ends of the first elastic bridge21may be pulled close to each other and both ends of the second elastic bridge22may be pulled close to each other. Then, the radius of curvature of the first elastic bridge21and the radius of curvature of the second elastic bridge22are reduced because of the contraction force of the variable length element23. Therefore, the movable frame12may be forced to move away from the fixed frame11.

In this case, the free ends of the pair of side frames13aare driven away from each other. To this end, the pair of side frames13amay include a bimetal element or a piezoelectric element that is bendable or extendable by temperature control or electrical control. For example, the pair of side frames13amay be bent in a curved shape when a driving voltage is applied thereto, and may stretch in a straight shape when the driving voltage is not applied thereto. In this case, while the distance between the fixed frame11and the movable frame12is changed, the driving device120may apply a driving voltage to the pair of side frames13aunder the control of the processor140to bend the pair of side frames13asuch that the free ends of the pair of side frames13awhich face each other may be moved away from each other as shown inFIG. 2B. Then, the movable frame12is moved away from the fixed frame11while being pushed by the second elastic bridge22.

Thereafter, when the movable frame12passes by the positions of the second protrusions13c, the driving device120stops applying the driving voltage to the variable length element23and the driving voltage to the pair of side frames13aunder the control of the processor140. As a result, the pair of side frames13astretch in a straight shape, and the free ends of the pair of side frames13abecome close to each other. In addition, due to the elastic restoring force of the first elastic bridge21and the second elastic bridge22, the movable frame12may be forced to move toward to the fixed frame11. Therefore, both sides of the movable frame12are brought into contact with the second protrusions13cand are not further moved toward the fixed frame11because of the second protrusions13c, such that the position of the movable frame12is fixed. Then, as shown inFIG. 2B, the image forming device110fixed to the movable frame12is fixed at a position closer to the combiner member130than the position as shown inFIG. 2A.

When the image forming device110is moved from the position shown inFIG. 2Bback to the position shown inFIG. 2A, the driving device120applies a driving voltage only to the pair of side frames13aunder the control of the processor140. Then, as the pair of side frames13aare bent, the free ends of the pair of side frames13aare moved away from each other. At this time, because of the elastic restoring force of the first elastic bridge21and the second elastic bridge22, the movable frame12may be forced to move toward to the fixed frame11. Then, when the movable frame12passes by the positions of the second protrusions13c, the driving device120stops applying the driving voltage to the pair of side frames13a. As a result, both side surfaces of the movable frame12are caught by the first protrusions13bas the pair of side frames13astretch in a straight shape.

As described above, the pair of side frames13aare operated in such a manner that the pair of side frames13aare in a bent state having a curved shape while the distance between the fixed frame11and the movable frame12is changed and are in a straight state while the distance between the fixed frame11and the movable frame12is maintained. Therefore, while the distance between the fixed frame11and the movable frame12is changed, the mutually-facing free ends of the pair of side frames13aare moved away from each other, and thus the movable frame12is allowed to move. While the distance between the fixed frame11and the movable frame12is maintained, the mutually-facing free ends of the pair of side frames13abecome closer to each other than in the bent state, and thus the fixed frame11is caught by the first protrusions13bor the second protrusions13cand may not move.

In addition, when the image forming device110is moved from the position shown inFIG. 2Ato the position shown inFIG. 2B, driving voltage is applied to both the variable length element23and the pair of side frames13a. When the image forming device110is moved from the position shown inFIG. 2Bto the position shown inFIG. 2A, driving voltage is applied to only the pair of side frames13a. In addition, while the image forming device110is fixed at the position shown inFIG. 2Aor the position shown inFIG. 2B, no voltage is applied to both the variable length element23and the pair of side frames13a.

Therefore, in the display apparatus100of the example embodiment, power is consumed only while the position of the image forming device110is changed to change the depth of an image that the viewer views. While the depth of an image is maintained, since the position of the image forming device110is fixed using the fixing member30, power is not consumed. Therefore, according to the example embodiment, power consumption of the display apparatus100may be reduced while the depth of an image is maintained.

Meanwhile, the pair of side frames13aare not limited to bimetal elements or piezoelectric elements. For example,FIGS. 3A and 3Bare views schematically illustrating a structure and operation of the fixing member30according to another example embodiment. Referring toFIGS. 3A and 3B, the fixing member30may further include variable length elements26fixed between the free ends and the fixed ends of the pair of side frames13a. In this case, each of the pair of side frames13amay include a plate-like material having elastic restoring force such as a metal or a plastic. For example, each of the pair of side frames13amay have elastic restoring force in a stretching direction thereof. For example, the pair of side frames13amay have elastic restoring force in directions in which the mutually-facing free ends of the pair of side frames13aapproach each other.

While the distance between the fixed frame11and the movable frame12is changed, the driving device120applies a driving voltage to the variable length elements26under the control of the processor140to contract the variable length elements26as shown inFIG. 3A. Then, the free ends of the pair of side frames13aare moved away from each other while being bent. While the distance between the fixed frame11and the movable frame12is maintained, the driving voltage is not applied to the variable length elements26as shown inFIG. 3B. Then, the lengths of the variable length elements26increases, and the pair of side frames13abecome straight due to the elastic restoring force thereof. Therefore, the free ends of the pair of side frames13abecome closer to each other than when they are bent.

FIGS. 4A and 4Bare views schematically illustrating a structure and operation of a driving device120aaccording to another example embodiment. Referring toFIGS. 4A and 4B, the driving device120amay include a fixed frame11which is fixed to the inside of the display apparatus100, a movable frame12which is arranged to face the fixed frame11and is movable; an actuator20which is configured to change the distance between the fixed frame11and the movable frame12, and a fixing member40which is configured to fix the distance between the fixed frame11and the movable frame12. The driving device120ashown inFIGS. 4A and 4Bis different from the driving device120shown inFIGS. 2A and 2Bin terms of the structure of the fixing member40.

The fixing member40may include a pair of first rods31rotatably arranged at both side edges of the fixed frame11, and a pair of second rods32rotatably arranged at both side edges of the movable frame12. For example, the pair of first rods31may be rotatably fixed to a lower surface of the fixed frame11via hinges33, and the pair of second rods32may be rotatably fixed to an upper surface of the movable frame12via hinges34.

To adjust the distance between the fixed frame11and the movable frame12, end portions of the pair of first rods31and corresponding end portions of the pair of second rods32may be configured to make contact with each other and interfere with each other. For example, the end portions of the pair of first rods31may include recesses31aand barriers31bsurrounding the recesses31a. In addition, the end portions of the pair of second rods32may be placed in the recesses31aof the pair of first rods31which correspond thereto. The widths of the end portions of the pair of second rods32may be respectively less than the widths of the recesses31aof the pair of first rods31which correspond thereto, such that the end portions of the pair of second rods32may move within predetermined ranges inside the recesses31a. That is, in the recesses31a, there may be predetermined gaps between the end portions of the pair of second rods32and the barriers31b. The recesses31aand the end portions of the pair of second rods32may have a straight shape, but are not limited thereto and may have, for example, a circular shape or polygonal shape. For example, the recesses31amay be provided in the form of circular hollow cylinders or polygonal hollow cylinders, and the end portions of the pair of second rods32may be provided in the form of cylindrical or polygonal solid cylinders.

InFIGS. 4A and 4B, the recesses31aand the barriers31bare formed at the pair of first rods31, but embodiments are not limited thereto. In another example embodiment, the recesses31aand the barriers31bmay be formed at the pair of second rods32instead of being formed at the pair of first rods31.

The fixing member40may have a first state in which the pair of first rods31and the pair of second rods32corresponding the pair of first rods31are fixed in a straight line with each other, and a second state in which the pair of first rods31and the pair of second rods32corresponding to the pair of first rods31are fixed in at an inclined angle with respect to each other. In the first state, the end portions of the pair of second rods32come into contact with bottom surfaces of the recesses31aof the pair of first rods31corresponding thereto, and the pair of first rods31and the pair of second rods32are restrained from moving further. Furthermore, in the second state, the end portions of the pair of second rods32come into contact with inner walls of the barriers31bof the pair of first rods31corresponding thereto, and at the same time, portions of the barriers31bof the pair of first rods31come into contact with side walls of the pair of second rods32corresponding thereto, such that the pair of first rods31and the pair of second rods32may be restrained from moving further.

As shown inFIG. 4A, the fixing member40is initially in the second state in which the pair of first rods31and the pair of second rods32corresponding to the pair of first rods31are fixed at an inclined angle with respect to each other. In the second state, the movable frame12is closer to the fixed frame11. Therefore, the image forming device110fixed to a lower surface of the movable frame12is distant from the light entrance surface of the combiner member130. Although the movable frame12may be forced to move toward the fixed frame11because of the elastic restoring force of a first elastic bridge21and a second elastic bridge22, the position of the movable frame12may be fixed because the end portions of the pair of second rods32are in contact with the inner walls of the barriers of the pair of first rods31, and thus are restrained from moving.

When the driving device120aapplies a driving voltage to the variable length element23under the control of the processor140, the variable length element23contracts such that both ends of the first elastic bridge21may be pulled close to each other and both ends of the second elastic bridge22may be pulled close to each other. Then, the radius of curvature of the first elastic bridge21and the radius of curvature of the second elastic bridge22are reduced because of the contraction force of the variable length element23. Therefore, the movable frame12may be forced to move away from the fixed frame11.

Then, as shown inFIG. 4B, the fixing member40enters into the second state in which the pair of first rods31and the pair of second rods32corresponding to the pair of first rods31are fixed in a straight line with each other. In the first state, the movable frame12is farther away from the fixed frame11than the second state. Therefore, the image forming device110fixed to the lower surface of the movable frame12is closer to the light entrance surface of the combiner member130.

After the pair of first rods31and the pair of second rods32corresponding to the pair of first rods31are completely arranged in a straight line with each other, the driving device120amay stop applying the driving voltage to the variable length element23. Then, the movable frame12may be forced toward the fixed frame11by the elastic restoring force of the first elastic bridge21and the second elastic bridge22. However, since the end portions of the pair of second rods32are in contact with the bottom surfaces of the recesses31aof the pair of first rods31, and thus are restrained from moving, the position of the movable frame12may be fixed.

In addition, the fixing member30may further include variable length elements35respectively connected between both side edges of the fixed frame11and the end portions of the pair of first rods31. For example, the variable length elements35may be connected between an upper surface of the fixed frame11and outer walls of the barriers31bof the pair of first rods31. When a driving voltage is applied to the variable length elements35, the variable length elements35may contract. Therefore, the pair of first rods31may rotate in outward directions of both sides of the fixed frame11as the end portions of the pair of first rods31are pulled.

When the image forming device110is moved from the position shown inFIG. 4Bto the position shown inFIG. 4A, the driving device120aapplies a driving voltage to the variable length elements35under the control of the processor140. Then, as the variable length elements35contract, the pair of first rods31rotate in the outward directions of both sides of the fixed frame11. In addition, as the pair of first rods31rotate, the pair of second rods32also rotate in the outward directions of both sides of the fixed frame11. When the pair of first rods31and the pair of second rods32rotate by a predetermined angle, the end portions of the pair of second rods32come into contact with the inner walls of the barriers31bof the pair of first rods31corresponding thereto, and at the same time, portions of the barriers31bof the pair of first rods31come into contact with the sides of the pair of second rods32corresponding thereto. Therefore, the pair of first rods31and the pair of second rods32are restrained from moving such that the movable frame12may be fixed.

As described above, when the fixing member40changes from the second state to the first state, the distance between the fixed frame11and the movable frame12increases. In this case, the image forming device110moves closer to the light entrance surface of the combiner member130. Driving voltage is applied only to the actuator20while the fixing member40is changed from the second state to the first state. When the fixing member40changes from the first state to the second state, the distance between the fixed frame11and the movable frame12decreases. In this case, the image forming device110is farther away from the light entrance surface of the combiner member130than in the first state. Driving voltage is applied only to the variable length elements35while the fixing member40is changed from the second state to the first state. In addition, power is not consumed while the distance between the fixed frame11and the movable frame12is maintained.

FIGS. 5A and 5bare views schematically illustrating a structure and operation of a driving device120baccording to another example embodiment. The structure of the driving device120bshown inFIGS. 5A and 5Bis similar to the structure of the driving device120ashown inFIGS. 4A and 4Bexcept for the structure of a fixing member50.

Referring toFIGS. 5A and 5B, the fixing member50may include a pair of first rods36rotatably arranged at both side edges of a fixed frame11, and a pair of second rods37rotatably arranged at both side edges of a movable frame12. For example, the pair of first rods36may be rotatably fixed to a lower surface of the fixed frame11via hinges33, and the pair of second rods37may be rotatably fixed to an upper surface of the movable frame12via hinges34. End portions of the pair of first rods36and end portions of the pair of second rods37corresponding thereto may have complementary shapes to engage with each other. For example, the end portions of the pair of first rods36may have a stepped shape, and the end portions of the pair of second rods37corresponding thereto may have a stepped shape complementary to the stepped shape of the end portions of the pair of first rods36.

The fixing member50may have a first state in which the pair of first rods36and the pair of second rods37corresponding the pair of first rods36are fixed in a straight line with each other, and a second state in which the pair of first rods36and the pair of second rods37corresponding to the pair of first rods36are fixed at an inclined angle with respect to each other. In the first state, the end portions of the pair of first rods36engage with the end portions of the pair of second rods37corresponding thereto such that the pair of first rods36and the pair of second rods37are restrained from moving further. In this case, lateral surfaces36aof the end portions of the pair of first rods36are in parallel with and in tight contact with lateral surfaces37aof the end portions of the pair of second rods37corresponding thereto. In addition, end surfaces36bof the end portions of the pair of first rods36are in contact with stop surfaces37cof the end portions of the pair of second rods37corresponding thereto, and end surfaces37bof the end portions of the pair of second rods37are in contact with stop surfaces36cof the end portions of the pair of first rods36corresponding thereto. In the second state, the end surfaces36bof the end portions of the pair of first rods36are in contact with the lateral surfaces37aof the end portions of the pair of second rods37corresponding thereto, and thus the pair of first rods36and the pair of second rods37are restrained from moving further.

In addition, the fixing member50may include first stoppers41arranged on the lower surface of the fixed frame11to limit the rotation angles of the pair of first rods36, and second stoppers42arranged on the upper surface of the movable frame12to limit the rotation angles of the pair of second rods37. The first stoppers41protrude from the lower surface of the fixed frame11around the hinges33of the pair of first rods36. Therefore, the rotations of the pair of first rods36are limited when the pair of first rods36come into contact the first stoppers41while the rotation angles of the pair of first rods36increase. The second stoppers42protrude from the upper surface of the movable frame12around the hinges34of the pair of second rods37. Therefore, the rotations of the pair of second rods37are limited when the pair of second rods37come into contact with the second stoppers42while the rotation angles of the pair of second rods37increase. The first and second stoppers41and42may also be applied to the example embodiment shown inFIGS. 4A and 4B.

In addition, the fixing member50may further include variable length elements35respectively connected between both side edges of the fixed frame11and the end portions of the pair of first rods36. The variable length elements35are contracted by electrical control to switch the fixing member50from the first state to the second state.

The operation of the driving device120bshown inFIGS. 5A and 5Bis similar to the operation of the driving device120ashown inFIGS. 4A and 4B. As shown inFIG. 5A, the fixing member50is initially in the second state in which the pair of first rods36and the pair of second rods37corresponding to the pair of first rods36are fixed at an inclined angle with respect to each other. In the second state, the image forming device110fixed to a lower surface of the movable frame12is farther away from the light entrance surface of the combiner member130than the first state. Although the movable frame12may be forced to move toward the fixed frame11by the elastic restoring force of a first elastic bridge21and a second elastic bridge22, the pair of first rods36and the pair of second rods37are restrained from moving further because the end surfaces37bof the end portions of the pair of second rods37are in contact with the lateral surfaces36aof the end portions of the pair of first rods36corresponding thereto, the pair of first rods36are in contact with the first stoppers41, and the pair of second rods37are in contact with the second stoppers42. Thus, the position of the movable frame12may be fixed.

When the depth of an image displayed on the image forming device110changes, the processor140controls the driving device120bto apply a driving voltage to a variable length element23. Then, since the variable length element23is contracted to further bend the first elastic bridge21and the second elastic bridge22, the movable frame12may be forced to move in a direction away from the fixed frame11. As a result, as shown inFIG. 5B, the fixing member50enters into the first state in which the pair of first rods36and the pair of second rods37corresponding to the pair of first rods36are fixed in a straight line with each other. At this time, the end portions of the pair of first rods36and the end portions of the pair of second rods37engage with each other, and thus the pair of first rods36and the pair of second rods37are restrained from moving further. Thus, the position of the movable frame12may be fixed.

When the image forming device110is moved from the position shown inFIG. 5Bto the position shown inFIG. 5A, the driving device120bapplies a driving voltage to the variable length elements35under the control of the processor140. Then, as the variable length elements35contract, the pair of first rods36rotate in outward directions of both sides of the fixed frame11. In addition, as the pair of second rods37are pushed by the pair of first rods36, the pair of second rods37are also rotated in the outward directions of both sides of the fixed frame11. When the pair of first rods36and the pair of second rods37rotate by a predetermined angle, the end surfaces36bof the end portions of the pair of first rods36come into contact with the lateral surfaces37aof the end portions of the pair of second rods37corresponding thereto, and thus the pair of first rods36and the pair of second rods37are restrained from moving further.

FIGS. 6A and 6bare views schematically illustrating a structure and operation of a driving device120caccording to another example embodiment. The structure of the driving device120cshown inFIGS. 6A and 6Bis similar to the structure of the driving device120bshown inFIGS. 5A and 5Bexcept for the structure of a fixing member60. Referring toFIGS. 6A and 6B, the fixing member60may include a pair of first rods46that are rotatable and arranged at both side edges of a fixed frame11, and a pair of second rods47that are rotatable and arranged at both side edges of a movable frame12. End portions of the pair of first rods46and end portions of the pair of second rods47corresponding thereto may have complementary shapes to engage with each other. For example, the end portions of the pair of first rods46may have a stepped shape, and the end portions of the pair of second rods47corresponding thereto may have a stepped shape complementary to the stepped shape of the end portions of the pair of first rods46.

The pair of first rods46and the pair of second rods47shown inFIGS. 6A and 6Bhave left-right reversed shapes compared to the pair of first rods36and the pair of second rods37shown inFIGS. 5A and 5B. Thus, in a second state in which the pair of first rods46and the pair of second rods47corresponding thereto are fixed at an inclined angle to each other, end surfaces47bof the end portions of the pair of second rods47are in contact with lateral surfaces46aof the end portions of the pair of first rods46corresponding thereto.

In addition, the fixing member60may further include variable length elements35respectively connected between both side edges of the movable frame12and the end portions of the pair of second rods47. When the fixing member60changes from a first state to the second state, the variable length elements35contract, and thus the pair of second rods47are rotated in outward directions of both sides of the movable frame12. In addition, as the pair of first rods46are pushed by the pair of second rods47, the pair of first rods46are also rotated in the outward directions of both sides of the movable frame12.

FIGS. 7A and 7Bare views schematically illustrating a structure and operation of a driving device120daccording to another example embodiment. Referring toFIGS. 7A and 7B, the driving device120dmay include a fixed frame11which is fixed to the inside of the display apparatus100, a movable frame12which is arranged to face the fixed frame11and is movable, an actuator70which is configured to change the distance between the fixed frame11and the movable frame12, and a fixing member80which is configured to fix the distance between the fixed frame11and the movable frame12.

The fixing member80may include a pair of first rods31rotatably arranged at both side edges of the fixed frame11, and a pair of second rods32rotatably arranged at both side edges of the movable frame12. End portions of the pair of first rods31and end portions of the pair of second rods32corresponding thereto may be configured to make contact with each other and interfere with each other. InFIGS. 7A and 7B, the fixing member80is illustrated as including the same pairs of first and second rods31and32as those shown inFIGS. 4A and 4B, but is not limited thereto. The fixing member80may include the pair of first rods36and the pair of second rods37which are shown inFIGS. 5A and 5B, or the pair of first rods46and the pair of second rods47which are shown inFIGS. 6A and 6B.

The actuator70may include first variable length elements38connected between the fixed frame11and inner lateral surfaces of the pair of first rods31, and second variable length elements39connected between the fixed frame11and outer lateral surfaces of the pair of first rods31. A length of the first variable length elements38and a length of the second variable length elements39may change by electrical control. For example, when a driving voltage is applied to the first variable length elements38and the second variable length elements39, the first variable length elements38and the second variable length elements39may contract and decrease in length. The first variable length elements38and the second variable length elements39may be connected to opposite lateral surfaces of the end portions of the pair of first rods31. For example, the first variable length elements38may be connected between the inner lateral surfaces of the pair of first rods31and near-center portions of a lower surface of the fixed frame11. In addition, the second variable length elements39may be connected between the outer lateral surfaces of the pair of first rods31and near-edge portions of the lower surface of the fixed frame11.

The fixing member80may have a first state in which the pair of first rods31and the pair of second rods32corresponding to the pair of first rods31are fixed in a straight line with each other, and a second state in which the pair of first rods31and the pair of second rods32corresponding to the pair of first rods31are fixed at an inclined angle with respect to each other. When the distance between the fixed frame11and the movable frame12is decreased, the first variable length elements38may be elongated and the second variable length elements39may be shortened as shown inFIG. 7Asuch that the fixing member80may be switched from the first state to the second state. To this end, the driving device120dmay apply a driving voltage to the second variable length elements39under the control of the processor140. After the fixing member80is switched to the second state, application of the driving voltage to the second variable length elements39may be stopped.

In addition, when the distance between the fixed frame11and the movable frame12is increased, the first variable length elements38may be shortened and the second variable length elements39may be elongated such that the fixing member80may be switched from the second state to the first state. To this end, the driving device120dmay apply a driving voltage to the first variable length elements38under the control of the processor140. After the fixing member80is switched to the first state, application of the driving voltage to the first variable length elements38may be stopped.

FIGS. 8A and 8Bare views schematically illustrating a structure and operation of a driving device120eaccording to another example embodiment. InFIGS. 7A and 7B, the first variable length elements38and the second variable length elements39are illustrated as being connected between the fixed frame11and the pair of first rods31. However, embodiments are not limited thereto. As shown inFIGS. 8A and 8B, first variable length elements38may be connected between near-center portions of an upper surface of the movable frame12and inner lateral surfaces of the pair of second rods32. In addition, second variable length elements39may be connected between near-edge portions of the upper surface of the movable frame12and outer lateral surfaces of the pair of second rods32. Apart from the configurations of the first variable length element38and the second variable length element39, the driving device120eshown inFIGS. 8A and 8Bhaving the same structure and operation as the driving device120dshown inFIGS. 7A and 7B.

The display apparatus100described above may provide images to only one eye of a viewer. However, display apparatus may be configured to provide images to both eyes of a viewer. For example,FIG. 9schematically illustrates a structure of a display apparatus200according to another example embodiment. Referring toFIG. 9, the display apparatus200of the example embodiment may include a left-eye image forming device110L configured to form left-eye images, a left-eye combiner member130L configured to provide the left-eye images to a viewer together with light containing and propagating from an outside landscape, a left-eye driving device120L configured to adjust the distance between the left-eye image forming device110L and the left-eye combiner member130L, a right-eye image forming device110R configured to form right-eye images, a right-eye combiner member130R configured to provide the right-eye images to the viewer together with light containing and propagating from the outside landscape, and a right-eye driving device120R configured to adjust the distance between the right-eye image forming device110R and the right-eye combiner member130R.

In addition,FIG. 10schematically illustrates a structure of a display apparatus300according to another example embodiment. Referring toFIG. 10, the display apparatus300of the example embodiment may include a left-eye image forming device110L configured to form left-eye images, a left-eye combiner member130L configured to provide the left-eye images to a viewer together with light containing and propagating from an outside landscape, a right-eye image forming device110R configured to form right-eye images, a right-eye combiner member130R configured to provide the right-eye images to the viewer together with light containing and propagating from the outside landscape, and a driving device120RL configured to adjust the positions of the left-eye image forming device110L and the right-eye image forming device110R. The driving device120RL may simultaneously adjust the distance between the right-eye image forming device110R and the right-eye combiner member130R and the distance between the left-eye image forming device110L and the left-eye combiner member130L.

The combiner member130described above may have an integral structure in which the focusing optical system131and the beam splitter132are fixed through the light guide plate133which is transparent. However, the structure of the combiner member130is not limited thereto and may have various other structures. For example,FIG. 11is a schematic view illustrating a structure and operation of a display apparatus400according to another example embodiment. Referring toFIG. 11, the display apparatus400may include an image forming device110, a combiner member230, a driving device120, and a processor140.

The combiner member230may include a beam splitter232and a concave mirror231. The beam splitter232may be a half mirror that reflects a portion of incident light and transmits the other portion of the incident light, or may be a polarization beam splitter light that reflects light having a first linear polarization component and transmits light having a second linear polarization component which is perpendicular to the first linear polarization component. The concave mirror231is configured to reflect light propagating from beam splitter232to focus the light on a viewer's eye. In addition, the concave mirror231may be configured to transmit light propagating from the outside to the viewer's eye. To this end, the concave mirror231may have a concave reflective surface231afacing the beam splitter232and a light-transmissive surface231bwhich is opposite the reflective surface231a.

In addition, when the image forming device110is a non-emissive image forming device such as an LCoS device or an LCD device, elements in addition to the display panel may be fixed to the movable frame12. For example,FIG. 12schematically illustrates the configuration of an image forming device110and a driving device120of a display apparatus500according to another example embodiment. Referring toFIG. 12, a light source301configured to provide illumination light, a beam splitter302configured to adjust the path of the illumination light, and a spatial light modulator310may be fixed together to a movable frame12.

The display apparatuses according to the above-described example embodiments may constitute wearable devices. In other words, the display apparatuses may be applied to wearable devices. For example, the display apparatuses may be applied to head mounted displays (HMD), glasses-type displays, goggle-type displays, or the like. Wearable electronic devices to which the display apparatuses of the above-described example embodiments are applied may be operated in conjunction with smartphones. The display apparatuses may be head-mounted, glasses-type, or goggle-type VR display apparatuses, AR display apparatuses, or MR display apparatuses which are capable of providing VR or providing virtual images together with a real outside landscape.

In addition, the display apparatuses may be provided in smartphones, and the smartphones may be used as VR, AR, or MR display apparatuses. For example, the display apparatuses may be applied to small electronic devices such as mobile electronic devices. In addition, the display apparatuses may be used in various other fields. For example, the display apparatuses may be used in the field of VR, AR, or MR and in other fields as well. For example, the display apparatuses may also be applied to small televisions or small monitors configured to be worn by users.

While the display apparatuses capable of multi-depth expression have been described according to example embodiments with reference to the accompanying drawings, the example embodiments are merely examples, and it will be understood by those of ordinary skill in the art that various modifications and other equivalent embodiments may be made therein without departing from the spirit and scope of the present disclosure. Therefore, the example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. The scope of the present disclosure is defined not by the above description but by the following claims, and all differences within equivalent ranges of the scope of the present disclosure should be considered as being included in the scope of the present disclosure.