Patent Description:
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.

<CIT>) discloses a device for generating a 3D light field. The device comprises a first lens having a fixed focal length, and an imaging element arranged to send light into the first lens and configured to send the light from different positions within a defined distance on the optical axis of the first lens.

<CIT>) discloses a virtual reality headset configured for displaying a three-dimensional (3D) virtual scene and including a varifocal element to dynamically adjust a focal length of an optics block included in the virtual reality headset based on a location in the virtual scene where the user is looking.

<CIT>) discloses a lens driving mechanism comprising two link members formed to be square and bonded at either corner part, and configured to perform pantographic operation for displacing the lens upon actuation.

<CIT>) discloses a display apparatus including: a frame that is mounted on a head part of a viewer; and an image display device that is mounted on the frame. The image display device includes an image forming device, and an optical system that guides an image, which originates from the image forming device, into a pupil of the viewer.

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.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the example embodiments of the disclosure.

According to an aspect of an example embodiment, there is provided a display apparatus according to claim <NUM>. The display apparatus includes 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 includes 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 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.

The above and/or other aspects, features, and advantages of example embodiments will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:.

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> is a schematic view schematically illustrating a structure and operation of a display apparatus <NUM> according to an example embodiment. Referring to <FIG>, the display apparatus <NUM> of the example embodiment may include an image forming device <NUM> configured to form images, a combiner member <NUM>, for example, a light system, an optical system, or an optical device, configured to provide images formed by the image forming device <NUM> together with light containing and propagating from an outside landscape, a driving device <NUM> configured to adjust the distance between the image forming device <NUM> and the combiner member <NUM>, and a processor <NUM> configured to control the image forming device <NUM> and the driving device <NUM> according to information about the depths of images to be displayed.

The image forming device <NUM> forms images by modulating light according to information on images to be provided to a viewer. Images formed by the image forming device <NUM> may 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 device <NUM> may be general two-dimensional images, but embodiments are not limited thereto.

For example, the image forming device <NUM> may 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 device <NUM> may 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 device <NUM> is a self-emissive display device such as an OLED display device or a micro LED, the image forming device <NUM> may include only one display panel. When the image forming device <NUM> is a non-emissive display device such as an LCoS device or an LCD device, the image forming device <NUM> may further include a light source configured to provide illumination light and a beam splitter configured to adjust the path of illumination light.

The combiner member <NUM> may change the path of an image formed by the image forming device <NUM> and 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 member <NUM> may include a focusing optical system <NUM> and may also include a beam splitter <NUM> configured to change the path of light by splitting the light. The focusing optical system <NUM> may be an imaging member having refractive power and configured to enlarge or reduce images formed by the image forming device <NUM>. In <FIG>, the focusing optical system <NUM> is illustrated as a concave mirror, but embodiments are not limited thereto. For example, the focusing optical system <NUM> may be provided as a combination of a convex lens, a concave lens, and the like.

The beam splitter <NUM> may 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 splitter <NUM> may be a polarization beam splitter that transmits or reflects incident light according to the polarization of the incident light. When the beam splitter <NUM> is a polarization beam splitter, additional optical elements for polarization conversion may be further included in the combiner member <NUM>.

As shown in <FIG>, the combiner member <NUM> may have an integrated structure in which the focusing optical system <NUM> and the beam splitter <NUM> are fixed through a transparent light guide plate <NUM>. For example, the beam splitter <NUM> may be arranged in a diagonal direction inside the light guide plate <NUM>, and an end portion of the light guide plate <NUM> may have a convexly curved surface. A concave mirror may be formed on the end portion of the light guide plate <NUM> by coating the convexly curved surface of the light guide plate <NUM> with a reflective film. In this example embodiment, an image formed by the image forming device <NUM> enters the inside of the light guide plate <NUM> through a light entrance surface of the light guide plate <NUM>. Thereafter, the image may be transmitted through the beam splitter <NUM>, enlarged and reflected by the focusing optical system <NUM>, and then reflected by the beam splitter <NUM> onto the viewer's eye. However, this is an example, and the structure of the combiner member <NUM> is not limited thereto.

The combiner member <NUM> may not only transmit light L10 containing an image formed by the image forming device <NUM> to the viewer's eye, but may also transmit light L20 containing and propagating from a front outside landscape to the viewer's eye. For example, the light guide plate <NUM> and the beam splitter <NUM> of the combiner member <NUM> may be configured to transmit the light L20 containing and propagating from the outside landscape. The light L20 propagating 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 device <NUM>. Therefore, the display apparatus <NUM> may function as a see-through-type display. In this regard, the display apparatus <NUM> of the example embodiment may be used for implementing augmented reality (AR) or mixed reality (MR). For example, the display apparatus <NUM> of the example embodiment may be a near-eye AR display apparatus.

The combiner member <NUM> is not limited to the illustrated shape and structure. Additional optical elements may be further provided to transmit an image formed by the image forming device <NUM> to 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 device <NUM> reaches the viewer's eye along a propagating path in which the image is transmitted through the beam splitter <NUM>, reflected by the focusing optical system <NUM>, and then reflected by the beam splitter <NUM>. 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 apparatus <NUM> of 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 apparatus <NUM> may include the driving device <NUM> configured to change the position of the image forming device <NUM>. The driving device <NUM> may move the image forming device <NUM> in parallel such that the distance between the image forming device <NUM> and the focusing optical system <NUM> of the combiner member <NUM> may change. Then, when the position of the image forming device <NUM> is changed in directions A1, the position of the virtual image plane VP may be changed in directions A2. For example, when the image forming device <NUM> is moved away from the focusing optical system <NUM> of the combiner member <NUM>, 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 processor <NUM> may generate a light modulation signal SG1 and a driving signal SG2 which are to be respectively transmitted to the image forming device <NUM> and the driving device <NUM> according to information about an image that the viewer will recognize. The image forming device <NUM> and the driving device <NUM> may be controlled respectively by the light modulation signal SG1 and the driving signal SG2 generated by the processor <NUM>. For example, the image forming device <NUM> forms an image based on the light modulation signal SG1 provided from the processor <NUM>. In addition, the driving device <NUM> adjusts the position of the image forming device <NUM> based on the driving signal SG2 provided from the processor <NUM> such that the virtual image plane VP may be positioned in accordance with the depth of the image formed by the image forming device <NUM>. To this end, the processor <NUM> may generate the driving signal SG2 by determining the distance between the image forming device <NUM> and the combiner member <NUM> based on information about the depth of the image which is included in the light modulation signal SG1 to be transmitted to the image forming device <NUM>.

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 processor <NUM> may 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 processor <NUM> may generate the driving signal SG2 to place the image forming device <NUM> such 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 SG1 and the driving signal SG2 generated by the processor <NUM> are respectively transmitted to the image forming device <NUM> and the driving device <NUM>, 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 SG2 for driving the driving device <NUM> may 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 device <NUM> employed in the display apparatus <NUM> of the example embodiment may include a shape-variable material to widen the position driving range of the image forming device <NUM> while reducing the volume of the driving device <NUM> as much as possible. For example, the driving device <NUM> may move the image forming device <NUM> while being changed in shape according to a signal applied to the driving device <NUM>. For this variable shape, the driving device <NUM> may include a material of which the shape is changed in a certain condition. For example, <FIG> and <FIG> are views schematically illustrating a structure and operation of the driving device <NUM> according to an example embodiment.

Referring to <FIG>, the driving device <NUM> includes a fixed frame <NUM> which may be fixed to the inside of the display apparatus <NUM>, a movable frame <NUM> which is arranged to face the fixed frame <NUM> and is movable, an actuator <NUM> which is configured to change the distanced between the fixed frame <NUM> and the movable frame <NUM>, and a fixing member <NUM> configured to fix the distance between the fixed frame <NUM> and the movable frame <NUM>. The fixed frame <NUM> and the movable frame <NUM> may have flat plate shapes which are parallel to each other. The movable frame <NUM> may be configured to be movable in a direction perpendicular to a surface facing the fixed frame <NUM>. In addition, the driving device <NUM> may further include a driving circuit for applying a driving voltage to the actuator <NUM> under the control of the processor <NUM>.

The image forming device <NUM> may be fixed to a lower surface of the movable frame <NUM> and may face the light entrance surface of the combiner member <NUM>. For example, the image forming device <NUM> may be a display panel of a self-emissive display device.

The actuator <NUM> is configured to move the movable frame <NUM> to change the distance between the fixed frame <NUM> and the movable frame <NUM>. The actuator <NUM> includes a first elastic bridge <NUM> having a curved surface which is convex toward the fixed frame <NUM>, a second elastic bridge <NUM> having a curved surface which is convex toward the movable frame <NUM>, and a variable length element <NUM> fixed between both ends of the first elastic bridge <NUM> and both ends of the second elastic bridge <NUM> and having a variable length.

The first elastic bridge <NUM> and the second elastic bridge <NUM> may include a plate-like elastic material such as a metal or plastic. Since both ends of the first elastic bridge <NUM> and both ends of the second elastic bridge <NUM> are fixed to the variable length element <NUM> which is shorter than the length of the first elastic bridge <NUM> and the length of the second elastic bridge <NUM>, respectively, the first elastic bridge <NUM> and the second elastic bridge <NUM> may be curved in an arch shape by the variable length element <NUM>. Therefore, each of the first elastic bridge <NUM> and the second elastic bridge <NUM> has elastic restoring force in a direction in which the radius of curvature thereof increases. A convex center portion of the first elastic bridge <NUM> may be fixed to a lower surface of the fixed frame <NUM>, for example, by using a fixing plate <NUM>. In addition, a convex center portion of the second elastic bridge <NUM> may be fixed to an upper surface of the movable frame <NUM>, for example, by using a fixing plate <NUM>. Then, when the first elastic bridge <NUM> and the second elastic bridge <NUM> are elastically deformed, the convex center portion of the first elastic bridge <NUM> may not move on the lower surface of the fixed frame <NUM>, and the convex center portion of the second elastic bridge <NUM> may not move on the upper surface of the movable frame <NUM>.

The variable length element <NUM> may be configured to be changed in length by electrical control. For example, the variable length element <NUM> may 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 element <NUM>, heat may be generated in the variable length element <NUM>, and the variable length element <NUM> may contract because of the heat. In addition, when the driving voltage is not applied to the variable length element <NUM>, the variable length element <NUM> may extend to its original length.

The fixing member <NUM>, which fixes the distance between the fixed frame <NUM> and the movable frame <NUM> while the movable frame <NUM> is not moving, may include, for example, a pair of side frames 13a respectively fixed to both side edges of the fixed frame <NUM>. Each of the pair of side frames 13a may include a plate-shaped elastic material extending in a direction from the fixed frame <NUM> toward the movable frame <NUM>. In addition, the pair of side frames 13a may include fixed ends which are fixed to the fixed frame <NUM> and free ends which are opposite the fixed ends. The free ends of the pair of side frames 13a may face both sides of the movable frame <NUM>.

In addition, the pair of side frames 13a may include a plurality of first and second protrusions 13b and 13c protruding from surfaces of the free ends such that the first protrusion 13b and the second protrusion 13c may make contact with both sides of the movable frame <NUM> to restrain the movable frame <NUM> from moving. The first protrusion 13b and the second protrusion 13c may be located at different distances from the fixed frame <NUM> in the direction from the fixed frame <NUM> toward the movable frame <NUM>. For example, the first protrusions 13b may be arranged at a first distance from the fixed frame <NUM>, and the second protrusions 13c may be are arranged at a second distance from the fixed frame <NUM> which is greater than the first distance. Thus, when both sides of the movable frame <NUM> are in contact with the first protrusions 13b, the movable frame <NUM> may be fixed at the first distance from the fixed frame <NUM>, and when both sides of the movable frame <NUM> are in contact with the second protrusions 13c, the movable frame <NUM> may be fixed at the second distance from the fixed frame <NUM>.

In an initial state, the variable length element <NUM> may not be contracted. In addition, as shown in <FIG>, both sides of the movable frame <NUM> may be located between the first protrusions 13b and the second protrusions 13c. The movable frame <NUM> may be forced to move toward the fixed frame <NUM> because of the elastic restoring force of the first elastic bridge <NUM> and the second elastic bridge <NUM>. Therefore, both sides of the movable frame <NUM> are brought into contact with the first protrusions 13b and are not further moved toward the fixed frame <NUM> because of the first protrusions 13b, such that the position of the movable frame <NUM> is fixed. Then, the image forming device <NUM> fixed to the movable frame <NUM> is also fixed at a position relatively distant from the combiner member <NUM>.

When the driving device <NUM> applies a driving voltage to the variable length element <NUM> under the control of the processor <NUM>, the variable length element <NUM> contracts such that both ends of the first elastic bridge <NUM> may be pulled close to each other and both ends of the second elastic bridge <NUM> may be pulled close to each other. Then, the radius of curvature of the first elastic bridge <NUM> and the radius of curvature of the second elastic bridge <NUM> are reduced because of the contraction force of the variable length element <NUM>. Therefore, the movable frame <NUM> may be forced to move away from the fixed frame <NUM>.

In this case, the free ends of the pair of side frames 13a are driven away from each other. To this end, the pair of side frames 13a may 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 frames 13a may 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 frame <NUM> and the movable frame <NUM> is changed, the driving device <NUM> may apply a driving voltage to the pair of side frames 13a under the control of the processor <NUM> to bend the pair of side frames 13a such that the free ends of the pair of side frames 13a which face each other may be moved away from each other as shown in <FIG>. Then, the movable frame <NUM> is moved away from the fixed frame <NUM> while being pushed by the second elastic bridge <NUM>.

Thereafter, when the movable frame <NUM> passes by the positions of the second protrusions 13c, the driving device <NUM> stops applying the driving voltage to the variable length element <NUM> and the driving voltage to the pair of side frames 13a under the control of the processor <NUM>. As a result, the pair of side frames 13a stretch in a straight shape, and the free ends of the pair of side frames 13a become close to each other. In addition, due to the elastic restoring force of the first elastic bridge <NUM> and the second elastic bridge <NUM>, the movable frame <NUM> may be forced to move toward to the fixed frame <NUM>. Therefore, both sides of the movable frame <NUM> are brought into contact with the second protrusions 13c and are not further moved toward the fixed frame <NUM> because of the second protrusions 13c, such that the position of the movable frame <NUM> is fixed. Then, as shown in <FIG>, the image forming device <NUM> fixed to the movable frame <NUM> is fixed at a position closer to the combiner member <NUM> than the position as shown in <FIG>.

When the image forming device <NUM> is moved from the position shown in <FIG> back to the position shown in <FIG>, the driving device <NUM> applies a driving voltage only to the pair of side frames 13a under the control of the processor <NUM>. Then, as the pair of side frames 13a are bent, the free ends of the pair of side frames 13a are moved away from each other. At this time, because of the elastic restoring force of the first elastic bridge <NUM> and the second elastic bridge <NUM>, the movable frame <NUM> may be forced to move toward to the fixed frame <NUM>. Then, when the movable frame <NUM> passes by the positions of the second protrusions 13c, the driving device <NUM> stops applying the driving voltage to the pair of side frames 13a. As a result, both side surfaces of the movable frame <NUM> are caught by the first protrusions 13b as the pair of side frames 13a stretch in a straight shape.

As described above, the pair of side frames 13a are operated in such a manner that the pair of side frames 13a are in a bent state having a curved shape while the distance between the fixed frame <NUM> and the movable frame <NUM> is changed and are in a straight state while the distance between the fixed frame <NUM> and the movable frame <NUM> is maintained. Therefore, while the distance between the fixed frame <NUM> and the movable frame <NUM> is changed, the mutually-facing free ends of the pair of side frames 13a are moved away from each other, and thus the movable frame <NUM> is allowed to move. While the distance between the fixed frame <NUM> and the movable frame <NUM> is maintained, the mutually-facing free ends of the pair of side frames 13a become closer to each other than in the bent state, and thus the fixed frame <NUM> is caught by the first protrusions 13b or the second protrusions 13c and may not move.

In addition, when the image forming device <NUM> is moved from the position shown in <FIG> to the position shown in <FIG>, driving voltage is applied to both the variable length element <NUM> and the pair of side frames 13a. When the image forming device <NUM> is moved from the position shown in <FIG> to the position shown in <FIG>, driving voltage is applied to only the pair of side frames 13a. In addition, while the image forming device <NUM> is fixed at the position shown in <FIG> or the position shown in <FIG>, no voltage is applied to both the variable length element <NUM> and the pair of side frames 13a.

Therefore, in the display apparatus <NUM> of the example embodiment, power is consumed only while the position of the image forming device <NUM> is 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 device <NUM> is fixed using the fixing member <NUM>, power is not consumed. Therefore, according to the example embodiment, power consumption of the display apparatus <NUM> may be reduced while the depth of an image is maintained.

Meanwhile, the pair of side frames 13a are not limited to bimetal elements or piezoelectric elements. For example, <FIG> are views schematically illustrating a structure and operation of the fixing member <NUM> according to another example embodiment. Referring to <FIG>, the fixing member <NUM> may further include variable length elements <NUM> fixed between the free ends and the fixed ends of the pair of side frames 13a. In this case, each of the pair of side frames 13a may include a plate-like material having elastic restoring force such as a metal or a plastic. For example, each of the pair of side frames 13a may have elastic restoring force in a stretching direction thereof. For example, the pair of side frames 13a may have elastic restoring force in directions in which the mutually-facing free ends of the pair of side frames 13a approach each other.

While the distance between the fixed frame <NUM> and the movable frame <NUM> is changed, the driving device <NUM> applies a driving voltage to the variable length elements <NUM> under the control of the processor <NUM> to contract the variable length elements <NUM> as shown in <FIG>. Then, the free ends of the pair of side frames 13a are moved away from each other while being bent. While the distance between the fixed frame <NUM> and the movable frame <NUM> is maintained, the driving voltage is not applied to the variable length elements <NUM> as shown in <FIG>. Then, the lengths of the variable length elements <NUM> increases, and the pair of side frames 13a become straight due to the elastic restoring force thereof. Therefore, the free ends of the pair of side frames 13a become closer to each other than when they are bent.

<FIG> and <FIG> are views schematically illustrating a structure and operation of a driving device 120a according to another example embodiment. Referring to <FIG> and <FIG>, the driving device 120a may include a fixed frame <NUM> which is fixed to the inside of the display apparatus <NUM>, a movable frame <NUM> which is arranged to face the fixed frame <NUM> and is movable; an actuator <NUM> which is configured to change the distance between the fixed frame <NUM> and the movable frame <NUM>, and a fixing member <NUM> which is configured to fix the distance between the fixed frame <NUM> and the movable frame <NUM>. The driving device 120a shown in <FIG> and <FIG> is different from the driving device <NUM> shown in <FIG> and <FIG> in terms of the structure of the fixing member <NUM>.

The fixing member <NUM> may include a pair of first rods <NUM> rotatably arranged at both side edges of the fixed frame <NUM>, and a pair of second rods <NUM> rotatably arranged at both side edges of the movable frame <NUM>. For example, the pair of first rods <NUM> may be rotatably fixed to a lower surface of the fixed frame <NUM> via hinges <NUM>, and the pair of second rods <NUM> may be rotatably fixed to an upper surface of the movable frame <NUM> via hinges <NUM>.

To adjust the distance between the fixed frame <NUM> and the movable frame <NUM>, end portions of the pair of first rods <NUM> and corresponding end portions of the pair of second rods <NUM> may be configured to make contact with each other and interfere with each other. For example, the end portions of the pair of first rods <NUM> may include recesses 31a and barriers 31b surrounding the recesses 31a. In addition, the end portions of the pair of second rods <NUM> may be placed in the recesses 31a of the pair of first rods <NUM> which correspond thereto. The widths of the end portions of the pair of second rods <NUM> may be respectively less than the widths of the recesses 31a of the pair of first rods <NUM> which correspond thereto, such that the end portions of the pair of second rods <NUM> may move within predetermined ranges inside the recesses 31a. That is, in the recesses 31a, there may be predetermined gaps between the end portions of the pair of second rods <NUM> and the barriers 31b. The recesses 31a and the end portions of the pair of second rods <NUM> may have a straight shape, but are not limited thereto and may have, for example, a circular shape or polygonal shape. For example, the recesses 31a may be provided in the form of circular hollow cylinders or polygonal hollow cylinders, and the end portions of the pair of second rods <NUM> may be provided in the form of cylindrical or polygonal solid cylinders.

In <FIG> and <FIG>, the recesses 31a and the barriers 31b are formed at the pair of first rods <NUM>, but embodiments are not limited thereto. In another example embodiment, the recesses 31a and the barriers 31b may be formed at the pair of second rods <NUM> instead of being formed at the pair of first rods <NUM>.

The fixing member <NUM> may have a first state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding the pair of first rods <NUM> are fixed in a straight line with each other, and a second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed in at an inclined angle with respect to each other. In the first state, the end portions of the pair of second rods <NUM> come into contact with bottom surfaces of the recesses 31a of the pair of first rods <NUM> corresponding thereto, and the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving further. Furthermore, in the second state, the end portions of the pair of second rods <NUM> come into contact with inner walls of the barriers 31b of the pair of first rods <NUM> corresponding thereto, and at the same time, portions of the barriers 31b of the pair of first rods <NUM> come into contact with side walls of the pair of second rods <NUM> corresponding thereto, such that the pair of first rods <NUM> and the pair of second rods <NUM> may be restrained from moving further.

As shown in <FIG>, the fixing member <NUM> is initially in the second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed at an inclined angle with respect to each other. In the second state, the movable frame <NUM> is closer to the fixed frame <NUM>. Therefore, the image forming device <NUM> fixed to a lower surface of the movable frame <NUM> is distant from the light entrance surface of the combiner member <NUM>. Although the movable frame <NUM> may be forced to move toward the fixed frame <NUM> because of the elastic restoring force of a first elastic bridge <NUM> and a second elastic bridge <NUM>, the position of the movable frame <NUM> may be fixed because the end portions of the pair of second rods <NUM> are in contact with the inner walls of the barriers of the pair of first rods <NUM>, and thus are restrained from moving.

When the driving device 120a applies a driving voltage to the variable length element <NUM> under the control of the processor <NUM>, the variable length element <NUM> contracts such that both ends of the first elastic bridge <NUM> may be pulled close to each other and both ends of the second elastic bridge <NUM> may be pulled close to each other. Then, the radius of curvature of the first elastic bridge <NUM> and the radius of curvature of the second elastic bridge <NUM> are reduced because of the contraction force of the variable length element <NUM>. Therefore, the movable frame <NUM> may be forced to move away from the fixed frame <NUM>.

Then, as shown in <FIG>, the fixing member <NUM> enters into the second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed in a straight line with each other. In the first state, the movable frame <NUM> is farther away from the fixed frame <NUM> than the second state. Therefore, the image forming device <NUM> fixed to the lower surface of the movable frame <NUM> is closer to the light entrance surface of the combiner member <NUM>.

After the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are completely arranged in a straight line with each other, the driving device 120a may stop applying the driving voltage to the variable length element <NUM>. Then, the movable frame <NUM> may be forced toward the fixed frame <NUM> by the elastic restoring force of the first elastic bridge <NUM> and the second elastic bridge <NUM>. However, since the end portions of the pair of second rods <NUM> are in contact with the bottom surfaces of the recesses 31a of the pair of first rods <NUM>, and thus are restrained from moving, the position of the movable frame <NUM> may be fixed.

In addition, the fixing member <NUM> may further include variable length elements <NUM> respectively connected between both side edges of the fixed frame <NUM> and the end portions of the pair of first rods <NUM>. For example, the variable length elements <NUM> may be connected between an upper surface of the fixed frame <NUM> and outer walls of the barriers 31b of the pair of first rods <NUM>. When a driving voltage is applied to the variable length elements <NUM>, the variable length elements <NUM> may contract. Therefore, the pair of first rods <NUM> may rotate in outward directions of both sides of the fixed frame <NUM> as the end portions of the pair of first rods <NUM> are pulled.

When the image forming device <NUM> is moved from the position shown in <FIG> to the position shown in <FIG>, the driving device 120a applies a driving voltage to the variable length elements <NUM> under the control of the processor <NUM>. Then, as the variable length elements <NUM> contract, the pair of first rods <NUM> rotate in the outward directions of both sides of the fixed frame <NUM>. In addition, as the pair of first rods <NUM> rotate, the pair of second rods <NUM> also rotate in the outward directions of both sides of the fixed frame <NUM>. When the pair of first rods <NUM> and the pair of second rods <NUM> rotate by a predetermined angle, the end portions of the pair of second rods <NUM> come into contact with the inner walls of the barriers 31b of the pair of first rods <NUM> corresponding thereto, and at the same time, portions of the barriers 31b of the pair of first rods <NUM> come into contact with the sides of the pair of second rods <NUM> corresponding thereto. Therefore, the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving such that the movable frame <NUM> may be fixed.

As described above, when the fixing member <NUM> changes from the second state to the first state, the distance between the fixed frame <NUM> and the movable frame <NUM> increases. In this case, the image forming device <NUM> moves closer to the light entrance surface of the combiner member <NUM>. Driving voltage is applied only to the actuator <NUM> while the fixing member <NUM> is changed from the second state to the first state. When the fixing member <NUM> changes from the first state to the second state, the distance between the fixed frame <NUM> and the movable frame <NUM> decreases. In this case, the image forming device <NUM> is farther away from the light entrance surface of the combiner member <NUM> than in the first state. Driving voltage is applied only to the variable length elements <NUM> while the fixing member <NUM> is changed from the second state to the first state. In addition, power is not consumed while the distance between the fixed frame <NUM> and the movable frame <NUM> is maintained.

<FIG> and <FIG> are views schematically illustrating a structure and operation of a driving device 120b according to another example embodiment. The structure of the driving device 120b shown in <FIG> and <FIG> is similar to the structure of the driving device 120a shown in <FIG> and <FIG> except for the structure of a fixing member <NUM>.

Referring to <FIG> and <FIG>, the fixing member <NUM> may include a pair of first rods <NUM> rotatably arranged at both side edges of a fixed frame <NUM>, and a pair of second rods <NUM> rotatably arranged at both side edges of a movable frame <NUM>. For example, the pair of first rods <NUM> may be rotatably fixed to a lower surface of the fixed frame <NUM> via hinges <NUM>, and the pair of second rods <NUM> may be rotatably fixed to an upper surface of the movable frame <NUM> via hinges <NUM>. End portions of the pair of first rods <NUM> and end portions of the pair of second rods <NUM> corresponding thereto may have complementary shapes to engage with each other. For example, the end portions of the pair of first rods <NUM> may have a stepped shape, and the end portions of the pair of second rods <NUM> corresponding thereto may have a stepped shape complementary to the stepped shape of the end portions of the pair of first rods <NUM>.

The fixing member <NUM> may have a first state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding the pair of first rods <NUM> are fixed in a straight line with each other, and a second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed at an inclined angle with respect to each other. In the first state, the end portions of the pair of first rods <NUM> engage with the end portions of the pair of second rods <NUM> corresponding thereto such that the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving further. In this case, lateral surfaces 36a of the end portions of the pair of first rods <NUM> are in parallel with and in tight contact with lateral surfaces 37a of the end portions of the pair of second rods <NUM> corresponding thereto. In addition, end surfaces 36b of the end portions of the pair of first rods <NUM> are in contact with stop surfaces 37c of the end portions of the pair of second rods <NUM> corresponding thereto, and end surfaces 37b of the end portions of the pair of second rods <NUM> are in contact with stop surfaces 36c of the end portions of the pair of first rods <NUM> corresponding thereto. In the second state, the end surfaces 36b of the end portions of the pair of first rods <NUM> are in contact with the lateral surfaces 37a of the end portions of the pair of second rods <NUM> corresponding thereto, and thus the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving further.

In addition, the fixing member <NUM> may include first stoppers <NUM> arranged on the lower surface of the fixed frame <NUM> to limit the rotation angles of the pair of first rods <NUM>, and second stoppers <NUM> arranged on the upper surface of the movable frame <NUM> to limit the rotation angles of the pair of second rods <NUM>. The first stoppers <NUM> protrude from the lower surface of the fixed frame <NUM> around the hinges <NUM> of the pair of first rods <NUM>. Therefore, the rotations of the pair of first rods <NUM> are limited when the pair of first rods <NUM> come into contact the first stoppers <NUM> while the rotation angles of the pair of first rods <NUM> increase. The second stoppers <NUM> protrude from the upper surface of the movable frame <NUM> around the hinges <NUM> of the pair of second rods <NUM>. Therefore, the rotations of the pair of second rods <NUM> are limited when the pair of second rods <NUM> come into contact with the second stoppers <NUM> while the rotation angles of the pair of second rods <NUM> increase. The first and second stoppers <NUM> and <NUM> may also be applied to the example embodiment shown in <FIG> and <FIG>.

In addition, the fixing member <NUM> may further include variable length elements <NUM> respectively connected between both side edges of the fixed frame <NUM> and the end portions of the pair of first rods <NUM>. The variable length elements <NUM> are contracted by electrical control to switch the fixing member <NUM> from the first state to the second state.

The operation of the driving device 120b shown in <FIG> and <FIG> is similar to the operation of the driving device 120a shown in <FIG> and <FIG>. As shown in <FIG>, the fixing member <NUM> is initially in the second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed at an inclined angle with respect to each other. In the second state, the image forming device <NUM> fixed to a lower surface of the movable frame <NUM> is farther away from the light entrance surface of the combiner member <NUM> than the first state. Although the movable frame <NUM> may be forced to move toward the fixed frame <NUM> by the elastic restoring force of a first elastic bridge <NUM> and a second elastic bridge <NUM>, the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving further because the end surfaces 37b of the end portions of the pair of second rods <NUM> are in contact with the lateral surfaces 36a of the end portions of the pair of first rods <NUM> corresponding thereto, the pair of first rods <NUM> are in contact with the first stoppers <NUM>, and the pair of second rods <NUM> are in contact with the second stoppers <NUM>. Thus, the position of the movable frame <NUM> may be fixed.

When the depth of an image displayed on the image forming device <NUM> changes, the processor <NUM> controls the driving device 120b to apply a driving voltage to a variable length element <NUM>. Then, since the variable length element <NUM> is contracted to further bend the first elastic bridge <NUM> and the second elastic bridge <NUM>, the movable frame <NUM> may be forced to move in a direction away from the fixed frame <NUM>. As a result, as shown in <FIG>, the fixing member <NUM> enters into the first state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed in a straight line with each other. At this time, the end portions of the pair of first rods <NUM> and the end portions of the pair of second rods <NUM> engage with each other, and thus the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving further. Thus, the position of the movable frame <NUM> may be fixed.

When the image forming device <NUM> is moved from the position shown in <FIG> to the position shown in <FIG>, the driving device 120b applies a driving voltage to the variable length elements <NUM> under the control of the processor <NUM>. Then, as the variable length elements <NUM> contract, the pair of first rods <NUM> rotate in outward directions of both sides of the fixed frame <NUM>. In addition, as the pair of second rods <NUM> are pushed by the pair of first rods <NUM>, the pair of second rods <NUM> are also rotated in the outward directions of both sides of the fixed frame <NUM>. When the pair of first rods <NUM> and the pair of second rods <NUM> rotate by a predetermined angle, the end surfaces 36b of the end portions of the pair of first rods <NUM> come into contact with the lateral surfaces 37a of the end portions of the pair of second rods <NUM> corresponding thereto, and thus the pair of first rods <NUM> and the pair of second rods <NUM> are restrained from moving further.

<FIG> and <FIG> are views schematically illustrating a structure and operation of a driving device 120c according to another example embodiment. The structure of the driving device 120c shown in <FIG> and <FIG> is similar to the structure of the driving device 120b shown in <FIG> and <FIG> except for the structure of a fixing member <NUM>. Referring to <FIG> and <FIG>, the fixing member <NUM> may include a pair of first rods <NUM> that are rotatable and arranged at both side edges of a fixed frame <NUM>, and a pair of second rods <NUM> that are rotatable and arranged at both side edges of a movable frame <NUM>. End portions of the pair of first rods <NUM> and end portions of the pair of second rods <NUM> corresponding thereto may have complementary shapes to engage with each other. For example, the end portions of the pair of first rods <NUM> may have a stepped shape, and the end portions of the pair of second rods <NUM> corresponding thereto may have a stepped shape complementary to the stepped shape of the end portions of the pair of first rods <NUM>.

The pair of first rods <NUM> and the pair of second rods <NUM> shown in <FIG> and <FIG> have left- right reversed shapes compared to the pair of first rods <NUM> and the pair of second rods <NUM> shown in <FIG> and <FIG>. Thus, in a second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding thereto are fixed at an inclined angle to each other, end surfaces 47b of the end portions of the pair of second rods <NUM> are in contact with lateral surfaces 46a of the end portions of the pair of first rods <NUM> corresponding thereto.

In addition, the fixing member <NUM> may further include variable length elements <NUM> respectively connected between both side edges of the movable frame <NUM> and the end portions of the pair of second rods <NUM>. When the fixing member <NUM> changes from a first state to the second state, the variable length elements <NUM> contract, and thus the pair of second rods <NUM> are rotated in outward directions of both sides of the movable frame <NUM>. In addition, as the pair of first rods <NUM> are pushed by the pair of second rods <NUM>, the pair of first rods <NUM> are also rotated in the outward directions of both sides of the movable frame <NUM>.

<FIG> and <FIG> are views schematically illustrating a structure and operation of a driving device 120d according to another example embodiment. Referring to <FIG> and <FIG>, the driving device 120d may include a fixed frame <NUM> which is fixed to the inside of the display apparatus <NUM>, a movable frame <NUM> which is arranged to face the fixed frame <NUM> and is movable, an actuator <NUM> which is configured to change the distance between the fixed frame <NUM> and the movable frame <NUM>, and a fixing member <NUM> which is configured to fix the distance between the fixed frame <NUM> and the movable frame <NUM>.

The fixing member <NUM> may include a pair of first rods <NUM> rotatably arranged at both side edges of the fixed frame <NUM>, and a pair of second rods <NUM> rotatably arranged at both side edges of the movable frame <NUM>. End portions of the pair of first rods <NUM> and end portions of the pair of second rods <NUM> corresponding thereto may be configured to make contact with each other and interfere with each other. In <FIG> and <FIG>, the fixing member <NUM> is illustrated as including the same pairs of first and second rods <NUM> and <NUM> as those shown in <FIG> and <FIG>, but is not limited thereto. The fixing member <NUM> may include the pair of first rods <NUM> and the pair of second rods <NUM> which are shown in <FIG> and <FIG>, or the pair of first rods <NUM> and the pair of second rods <NUM> which are shown in <FIG> and <FIG>.

The actuator <NUM> may include first variable length elements <NUM> connected between the fixed frame <NUM> and inner lateral surfaces of the pair of first rods <NUM>, and second variable length elements <NUM> connected between the fixed frame <NUM> and outer lateral surfaces of the pair of first rods <NUM>. A length of the first variable length elements <NUM> and a length of the second variable length elements <NUM> may change by electrical control. For example, when a driving voltage is applied to the first variable length elements <NUM> and the second variable length elements <NUM>, the first variable length elements <NUM> and the second variable length elements <NUM> may contract and decrease in length. The first variable length elements <NUM> and the second variable length elements <NUM> may be connected to opposite lateral surfaces of the end portions of the pair of first rods <NUM>. For example, the first variable length elements <NUM> may be connected between the inner lateral surfaces of the pair of first rods <NUM> and near-center portions of a lower surface of the fixed frame <NUM>. In addition, the second variable length elements <NUM> may be connected between the outer lateral surfaces of the pair of first rods <NUM> and near-edge portions of the lower surface of the fixed frame <NUM>.

The fixing member <NUM> may have a first state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed in a straight line with each other, and a second state in which the pair of first rods <NUM> and the pair of second rods <NUM> corresponding to the pair of first rods <NUM> are fixed at an inclined angle with respect to each other. When the distance between the fixed frame <NUM> and the movable frame <NUM> is decreased, the first variable length elements <NUM> may be elongated and the second variable length elements <NUM> may be shortened as shown in <FIG> such that the fixing member <NUM> may be switched from the first state to the second state. To this end, the driving device 120d may apply a driving voltage to the second variable length elements <NUM> under the control of the processor <NUM>. After the fixing member <NUM> is switched to the second state, application of the driving voltage to the second variable length elements <NUM> may be stopped.

In addition, when the distance between the fixed frame <NUM> and the movable frame <NUM> is increased, the first variable length elements <NUM> may be shortened and the second variable length elements <NUM> may be elongated such that the fixing member <NUM> may be switched from the second state to the first state. To this end, the driving device 120d may apply a driving voltage to the first variable length elements <NUM> under the control of the processor <NUM>. After the fixing member <NUM> is switched to the first state, application of the driving voltage to the first variable length elements <NUM> may be stopped.

<FIG> and <FIG> are views schematically illustrating a structure and operation of a driving device 120e according to another example embodiment. In <FIG> and <FIG>, the first variable length elements <NUM> and the second variable length elements <NUM> are illustrated as being connected between the fixed frame <NUM> and the pair of first rods <NUM>. However, embodiments are not limited thereto. As shown in <FIG> and <FIG>, first variable length elements <NUM> may be connected between near-center portions of an upper surface of the movable frame <NUM> and inner lateral surfaces of the pair of second rods <NUM>. In addition, second variable length elements <NUM> may be connected between near-edge portions of the upper surface of the movable frame <NUM> and outer lateral surfaces of the pair of second rods <NUM>. Apart from the configurations of the first variable length element <NUM> and the second variable length element <NUM>, the driving device 120e shown in <FIG> and <FIG> having the same structure and operation as the driving device 120d shown in <FIG> and <FIG>.

The display apparatus <NUM> described 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> schematically illustrates a structure of a display apparatus <NUM> according to another example embodiment. Referring to <FIG>, the display apparatus <NUM> of the example embodiment may include a left-eye image forming device <NUM> configured to form left-eye images, a left-eye combiner member <NUM> configured to provide the left-eye images to a viewer together with light containing and propagating from an outside landscape, a left-eye driving device <NUM> configured to adjust the distance between the left-eye image forming device <NUM> and the left-eye combiner member <NUM>, a right-eye image forming device 110R configured to form right-eye images, a right-eye combiner member 130R 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 device 120R configured to adjust the distance between the right-eye image forming device 110R and the right-eye combiner member 130R.

In addition, <FIG> schematically illustrates a structure of a display apparatus <NUM> according to another example embodiment. Referring to <FIG>, the display apparatus <NUM> of the example embodiment may include a left-eye image forming device <NUM> configured to form left-eye images, a left-eye combiner member <NUM> 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 device 110R configured to form right-eye images, a right-eye combiner member 130R configured to provide the right-eye images to the viewer together with light containing and propagating from the outside landscape, and a driving device 120RL configured to adjust the positions of the left-eye image forming device <NUM> and the right-eye image forming device 110R. The driving device 120RL may simultaneously adjust the distance between the right-eye image forming device 110R and the right-eye combiner member 130R and the distance between the left-eye image forming device <NUM> and the left-eye combiner member <NUM>.

The combiner member <NUM> described above may have an integral structure in which the focusing optical system <NUM> and the beam splitter <NUM> are fixed through the light guide plate <NUM> which is transparent. However, the structure of the combiner member <NUM> is not limited thereto and may have various other structures. For example, <FIG> is a schematic view illustrating a structure and operation of a display apparatus <NUM> according to another example embodiment. Referring to <FIG>, the display apparatus <NUM> may include an image forming device <NUM>, a combiner member <NUM>, a driving device <NUM>, and a processor <NUM>.

The combiner member <NUM> may include a beam splitter <NUM> and a concave mirror <NUM>. The beam splitter <NUM> may 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 mirror <NUM> is configured to reflect light propagating from beam splitter <NUM> to focus the light on a viewer's eye. In addition, the concave mirror <NUM> may be configured to transmit light propagating from the outside to the viewer's eye. To this end, the concave mirror <NUM> may have a concave reflective surface 231a facing the beam splitter <NUM> and a light-transmissive surface 231b which is opposite the reflective surface 231a.

In addition, when the image forming device <NUM> is 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 frame <NUM>. For example, <FIG> schematically illustrates the configuration of an image forming device <NUM> and a driving device <NUM> of a display apparatus <NUM> according to another example embodiment. Referring to <FIG>, a light source <NUM> configured to provide illumination light, a beam splitter <NUM> configured to adjust the path of the illumination light, and a spatial light modulator <NUM> may be fixed together to a movable frame <NUM>.

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.

Claim 1:
A display apparatus comprising:
an image forming device (<NUM>) configured to form an image;
an optical system (<NUM>) configured to provide an output image by combining light containing an outside landscape with the image formed by the image forming device (<NUM>); and
a driving device (<NUM>, 120a, 120b, 120c, 102d, 120e) configured to adjust a distance between the image forming device (<NUM>) and the optical system (<NUM>),
wherein the driving device (<NUM>, 120a, 120b, 120c) comprises:
a fixed frame (<NUM>);
a movable frame (<NUM>) which faces the fixed frame (<NUM>) and is movable;
an actuator (<NUM>, <NUM>) configured to change a distance between the fixed frame (<NUM>) and the movable frame (<NUM>); and
a fixing member (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to be operated in a first state while the distance between the fixed frame (<NUM>) and the movable frame (<NUM>) is changed and to be operated in a second state while the distance between the fixed frame (<NUM>) and the movable frame (<NUM>) is maintained, such as to fix the distance between the fixed frame (<NUM>) and the movable frame (<NUM>) at a first distance or at a second distance greater than the first distance;
wherein the image forming device (<NUM>) is fixed to the movable frame (<NUM>);
wherein the actuator (<NUM>) comprises:
a first elastic bridge (<NUM>) having a curved surface which is convex toward the fixed frame (<NUM>);
a second elastic bridge (<NUM>) having a curved surface which is convex toward the movable frame (<NUM>);
a variable length element (<NUM>) fixed between both ends of the first elastic bridge (<NUM>) and both ends of the second elastic bridge (<NUM>), and respectively having a length that is variable.