Head mounted display with eyetracking capability

[0002] This invention relates to head mounted optical eye tracking apparatus, and in particular to a method and apparatus for the display of a virtual image to a user's eyes while tracking at least one of the user's eyes to detect its sight direction and this Patent Application claims the priority of U.S. Provisional Application 60/116040 filed Jan. 14. 1999.

[0003] In our electronic age, there is a continuing search to reduce the size of the instrumentation that can be used for electronic display of information to the user. The electronic display provides the user's eyes with an image, which can be either real or virtual. A real image refers to an image which is observed directly by the unaided human eye, e.g., a photograph or an electronic display as provided by a computer monitor. The virtual image is an image which, if a viewing surface were positioned at the apparent location of the virtual image, no image would be observed on the viewing surface. The virtual image facilitates enhanced miniaturization since the size or location of the viewing surface no longer limits its display location.

[0004] Head mounted virtual image display systems are well known as illustrated by: Jachinowicz et al in U.S. Pat. No. 5,224,198; Tosaki in U.S. Pat. No. 5,712,649; and Taniguchi et al in U.S. Pat. No. 5,790,284. In the classic head mounted display systems, the light rays emitted by the liquid crystal display (LCD) screen are directed by a lens onto a beam splitter. The beam splitter when oriented toward the user's eye enables the viewer to see the virtual image projected by the LCD

[0005] Hildeband et al in U.S. Pat. No. 5,625,372 teaches a compact virtual image display system in which he combines a virtual image display and an eye tracker into a compact unit with a light emitting diode (LED) ring 58 about an optic lens 26 and an liquid crystal display (LCD) with feed back controls. Unfortunately, his system is not susceptible to head mounted displays. Furness, III et al in U.S. Pat. No. 5,467,104 describe in FIG. 4 an eye tracking device with a charged couple device (CCD) array detector but not useful for head mounted displays.

[0006] There exists a serious need for a head mounted, virtual image display system that will cooperatively provide eye tracking of the sight direction whereby physically challenged people can interact with devices. The sight direction information is also needed to enhance local images displayed in head mounted devices, correct for some depth perception difficulties, enhanced psychological studies by noting eye reactions to virtual image displays and increased resolution at the gaze point of visual displays.

[0007] The first objective of the present invention is to provide the user with a head mounted display that has an integrated eye-tracking function.

[0008] The second object of this invention is to provide a head mounted optical display system wherein the optical system provides a means to display the virtual image.

[0009] The third objective of this invention is to provide a head mounted optical display system with multiple infrared-emitting diodes positioned symmetrically around the optical system.

[0010] The fourth objective of this invention is to provide a head mounted, virtual image eye-tracking display system wherein the reflected infrared radiation is optically focused on a CCD sensor after reflection from the eye.

[0011] The primary embodiment of this invention is exemplified by a head mounted optical eye tracking apparatus for a user comprising in combination: an optical system means for displaying virtual images to a user's eye; and, means for tracking at least one, preferably both, of the user's eyes to determine sight direction.

[0012] The method of the invention includes the critical steps of displaying a virtual image to a user's eye, positioning a multiple infrared radiation eye-tracking display means peripherally of one imaging lens and imaging the user's eye to compute sight direction by means invisible to the user.

[0013] Further objects and advantages of this invention will be apparent from the following detailed description of a presently preferred embodiment, which is illustrated schematically in the accompanying drawings.

[0014] FIG. 1 is illustrative of a classic prior art head mounted display.

[0015] FIG. 2 is illustrative of the virtual image, eye-tracking system of the invention.

[0016] FIG. 3 shows an expanded illustration of the features of FIG. 2.

[0017] FIG. 4 details the sequence of sight information processing.

[0018] FIG. 5 is illustrative of the head-mounted structure.

[0019] FIG. 6 sets forth the diverse applications of the invention.

[0020] FIG. 7ashows four LEDs reflections on user's cornea when the user is gazing straight ahead.

[0021] FIG. 7bshows four LEDs reflections on user's cornea when the user is gazing to the right.

[0022] Before explaining the disclosed embodiment of the present invention in detail it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments. Also, the terminology used herein is for the purpose of description and not of limitation.

[0023] As indicated in the discussion of the prior art, the head mounted display of virtual images is well known, e.g., see Jachinowicz et al in U.S. Pat. No. 5,224,198. This system is illustrated in FIG. 1 wherein the LCD screen 2 rays 3 are focused by an imaging 4 onto a beam splitter 5 which enables the viewer's eye 7 to see the virtual image 8 projected by the LCD screen 2.

[0024] FIG. 2 illustrates the integrated virtual, eye-tracking system of the invention. This illustration shows the common features of the prior art FIG. 1 along with the liquid crystal display (LCD) rays 3, an imaging system 4 though modified with Light Emitting Diodes (LED) 9, a beam splitter (hot mirror) 5, the viewer's eye 7 and the virtual image 8. LEDs 9 can be VTE 3372 diodes available from EG&G Electronics. The additive features illustrated in FIG. 2 also includes the computer information processing portion 10 such as an IBM 486 using Light Tools Software, a (CCD) sensor 11 such as an XC-77 manufactured by Sony with a V-1056SX lens from Marshal Electronics, a second beam splitter (cold mirror) 6 and the previously noted LED diodes 9 that are positioned adjacent to and peripherally of the imaging system 4. Splitters/Mirrors 5, 6 can be splitters/mirrors manufactured by Edmund Scientific. To facilitate the understanding of the invention, an eye-tracking means has been integrated with a head-mounted display by laying out at least one, but preferably four, near infrared LEDs around the imaging system 4 used to display the virtual images. The LEDs form virtual images behind the cornea that are imaged on the CCD sensor through the same optical system as the one used to display virtual images of the LCD screen. The processing of the location of those images on the sensor allows determining the sight direction.

[0025] Reference should now be made to FIG. 3 whose numerical designations are common to those used in FIGS. 1 and 2 and as will be seen in FIG. 5. In the succeeding discussion, both the preparation and operation of the eye-tracking virtual system of the invention will be laid out.

[0026] Now for the eye-tracking portion of the system of the invention. The LEDs 9 emit light at a wavelength equal to 900 nanometers which is reflected off the hot mirror 5 onto the cornea 14 of the eye 7. The reflected IR beam from the cornea 14 strikes the hot mirror 5 and is thereafter directed through the imaging system 4, passes through the cold mirror 6 (which reflects visible light and transmits the IR beam) and focused onto the CCD camera 11 where the beam (rays) data is processed by the computer 10 to determine the sight direction. The imaging lens of the imaging system 4 is shown as a single lens; however, it may be an imaging system 4 composed of several lenses. The hot mirror 5 transmits approximately 50% of the visible spectrum and as noted reflects approximately 100% of the IR light. The user's eye is imaged with near infrared light onto the CCD sensor 11.

[0027] The virtual image portion of the system is initiated by the LCD screen 2, which receives its visual information from the computer 10. The images on the LCD screen 2 are displayed by the imaging system 4 in the virtual environment. The rays 3 from the LCD screen 2 are reflected by the hot mirror 5 onto the cornea 14.

[0028] Reference should now be made to FIG. 4. The eye-tracking portion of the system of the invention processes the information as is seen in FIG. 4. The image of the eye 40 is processed through an image processing program 41 in computer 10 to provide data related to location of pupil 42 and the location 43 of the reflections of the LEDs. From this data, the sight direction of 44 is then applied to 45 to update the virtual environment and 46 for behavioural studies.

[0029] FIG. 5 illustrates a prototype of the device of the invention (head set) as would be positioned about the user's head with ear pieces 52 securing it in place. As earlier described in FIG. 3, the headset 54 is positioned on the head so that each eye 7 has LEDs 9 positioned peripherally around the imaging system 4 for beaming into each of the eyes 7 by reflection off hot mirror 5. This structure is positioned in the headset 54 and further includes as illustrated cold mirrors 6 and CCD sensors 11. The structure of FIG. 5 is electrically wired by wires 56 to computer 10 and LCD screen 2.

[0030] FIG. 6 sets forth the many diverse and wide applications of the device and method of the invention.

[0031] FIG. 7ais representation of the image of the pupil, cornea and iris of a user's eye with the reflections of the 4 LEDs when the user gazes straight ahead. When the user is gazing off axis, the reflections of the 4 LEDs on an image of the pupil, cornea and iris of the user's eye is represented in FIG. 7b. Location of the LEDs when the eye rotates. By computing the location of the center 72, of the entrance pupil and the barycenter of the images of the LEDs, one can derive the vector PH, H being the projection of P, 72, center of the pupil, on the optical axis and determine the sight direction with respect to the axis of the reference point.

[0032] The device described herein is fully integrated and provides eye-tracking without occlusion of the field of view. It overcomes the defect of heavy weight and large size of previous head-mounted displays using eye-tracking. The use of four off-axis LEDs improves accuracy of tracking. FIG. 6 shows the extraordinary diversity of potential applications possible with the eye-tracking, virtual reality device described herein. Thus, the device can be used to interact with other devices: to assist physically challenged people; to update virtual images that are widely used by the military, medical industry and video games; and, to detect sight direction information which can be used in the study of behavior.

[0033] While the invention has been described, disclosed, illustrated and shown in various terms of certain embodiments or modifications which it has presumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.