Active tuning of a torsional resonant structure

Details Active tuning of a torsional resonant structure Active tuning of a torsional resonant structure

1999-08-05

2001-07-03

Schuberg, Darren (Department: 2872)

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

C359S221200, C359S212100, C359S291000, C310S308000

Reexamination Certificate

active

06256131

ABSTRACT:

TECHNICAL FIELD
The present invention relates to scanned light devices and, more particularly, to scanned light beam displays and imaging devices for viewing or collecting images.
BACKGROUND OF THE INVENTION
A variety of techniques are available for providing visual displays of graphical or video images to a user. In many applications cathode ray tube type displays (CRTs), such as televisions and computer monitors produce images for viewing. Such devices suffer from several limitations. For example, CRTs are bulky and consume substantial amounts of power, making them undesirable for portable or head-mounted applications.
Matrix addressable displays, such as liquid crystal displays and field emission displays, may be less bulky and consume less power. However, typical matrix addressable displays utilize screens that are several inches across. Such screens have limited use in head mounted applications or in applications where the display is intended to occupy only a small portion of a user's field of view. Such displays have been reduced in size, at the cost of increasingly difficult processing and limited resolution or brightness. Also, improving resolution of such displays typically requires a significant increase in complexity.
One approach to overcoming many limitations of conventional displays is a scanned beam display, such as that described in U.S. Pat. No. 5,467,104 of Furness et al., entitled VIRTUAL RETINAL DISPLAY, which is incorporated herein by reference. As shown diagrammatically in
FIG. 1
, in one embodiment of a scanned beam display
40
, a scanning source
42
outputs a scanned beam of light that is coupled to a viewer's eye
44
by a beam combiner
46
. In some scanned displays, the scanning source
42
includes a scanner, such as scanning mirror or acousto-optic scanner, that scans a modulated light beam onto a viewer's retina. In other embodiments, the scanning source may include one or more light emitters that are rotated through an angular sweep.
The scanned light enters the eye
44
through the viewer's pupil
48
and is imaged onto the retina
59
by the cornea. In response to the scanned light the viewer perceives an image. In another embodiment, the scanned source
42
scans the modulated light beam onto a screen that the viewer observes. One example of such a scanner suitable for either type of display is described in U.S. Pat. No. 5,557,444 to Melville et al., entitled MINIATURE OPTICAL SCANNER FOR A TWO-AXIS SCANNING SYSTEM, which is incorporated herein by reference.
Sometimes such displays are used for partial or augmented view applications. In such applications, a portion of the display is positioned in the user's field of view and presents an image that occupies a region
43
of the user's field of view
45
, as shown in FIG.
2
A. The user can thus see both a displayed virtual image
47
and background information
49
. If the background light is occluded, the viewer perceives only the virtual image
47
, as shown in FIG.
2
B.
One difficulty that may arise with such displays is raster pinch, as will now be explained with reference to
FIGS. 3-5
. As shown diagrammatically in
FIG. 3
, the scanning source
42
includes an optical source
50
that emits a beam
52
of modulated light. In this embodiment, the optical source
50
is an optical fiber that is driven by one or more light emitters, such as laser diodes (not shown). A lens
53
gathers and focuses the beam
52
so that the beam
52
strikes a turning mirror
54
and is directed toward a horizontal scanner
56
. The horizontal scanner
56
is a mechanically resonant scanner that scans the beam
52
periodically in a sinusoidal fashion. The horizontally scanned beam then travels to a vertical scanner
58
that scans periodically to sweep the horizontally scanned beam vertically. For each angle of the beam
52
from the scanners
58
, an exit pupil expander
62
converts the beam
52
into a set of beams
63
. Eye coupling optics
60
collect the beams
63
and form a set of exit pupils
65
. The exit pupils
65
together act as an expanded exit pupil for viewing by a viewer's eye
64
. One such expander is described in U.S. Pat. No. 5,701,132 of Kollin et al., entitled VIRTUAL RETINAL DISPLAY WITH EXPANDED EXIT PUPIL, which is incorporated herein by reference. One skilled in the art will recognize that, for differing applications, the exit pupil expander
62
may be omitted, may be replaced or supplemented by an eye tracking system, or may have a variety of structures, including diffractive or refractive designs. For example, the exit pupil expander
62
may be a planar or curved structure and may create any number or pattern of output beams in a variety of patterns. Also, although only three exit pupils are shown in
FIG. 3
, the number of pupils may be almost any number. For example, in some applications a 15 by 15 array may be suitable.
Returning to the description of scanning, as the beam scans through each successive location in the beam expander
62
, the beam color and intensity is modulated in a fashion to be described below to form a respective pixel of an image. By properly controlling the color and intensity of the beam for each pixel location, the display
40
can produce the desired image.
Simplified versions of the respective waveforms of the vertical and horizontal scanners are shown in FIG.
4
. In the plane
66
(FIG.
3
), the beam traces the pattern
68
shown in FIG.
5
. Though
FIG. 5
shows only eleven lines of image, one skilled in the art will recognize that the number of lines in an actual display will typically be much larger than eleven. As can be seen by comparing the actual scan pattern
68
to a desired raster scan pattern
69
, the actual scanned beam
68
is “pinched” at the outer edges of the beam expander
62
. That is, in successive forward and reverse sweeps of the beam, the pixels near the edge of the scan pattern are unevenly spaced. This uneven spacing can cause the pixels to overlap or can leave a gap between adjacent rows of pixels. Moreover, because the image information is typically provided as an array of data, where each location in the array corresponds to a respective position in the ideal raster pattern
69
, the displaced pixel locations can cause image distortion.
For a given refresh rate and a given wavelength, the number of pixels per line is determined in the structure of
FIG. 3
by the mirror scan angle &thgr; and mirror dimension D perpendicular to the axis of rotation. For high resolution, it is therefor desirable to have a large scan angle &thgr; and a large mirror. However, larger mirrors and scan angles typically correspond to lower resonant frequencies. A lower resonant frequency provides fewer lines of display for a given period. Consequently, a large mirror and larger scan angle may produce unacceptable refresh rates.
One skilled in the art will recognize that scanning is an important function in such displays and in many other applications. For many applications it is desirable to have a small, high-performance, reliable scanning apparatus.
SUMMARY OF THE INVENTION
A display includes a primary scanning mechanism that simultaneously scans a plurality of beams of light both horizontally and vertically along substantially continuous scan paths where each beam defines a discrete “tile” of an image. In the preferred embodiment, the scanning mechanism includes a mirror that pivots to sweep the beams horizontally.
Optical sources are aligned to provide the beams of light to the scanning mechanism from respective input angles. The input angles are selected such that the scanning mechanism sweeps each beam of light across a respective distinct region of an image field. Because the respective regions are substantially non-overlapping, each beam of light generates a substantially spatially distinct region of the image. The respective regions are immediately adjacent or may overlap slightly, so that the spatially distinct regions are “tiled” to form a contiguous image. Because movement of the mirror p

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