This paper outlines the design trade-offs and measured results of scanner architectures for use in high resolution Retinal Scanning Displays: Mechanical resonant for horizontal scanning, and MEMS-based pinch correction and vertical linear scanners. Analysis steps and techniques used to model and minimize dynamic deformations are covered. This paper also discusses two types of scanners and associated mirror flatness issues. Dynamic flatness modeling and performance results are presented, followed by thermally induced deformations and possible athermalize solutions for MEMS-type scanning mirrors. Theory, FEA dynamic and thermal analysis, experimental results, and methods to reduce mirror deformation are discussed.
A high-frequency resonant horizontal scanner and a linearly driven vertical scanner at display frame rates can create a 2-D raster for video display. The combined motion of the two scanners forms a sinusoidal raster in the vertical direction where the raster line spacing is uniform only at the center and becomes progressively nonuniform towards the left and right edges of the display screen. Nonuniformities degrade the image quality and can be corrected by the addition of a third scanner to the system. Last year we reported the requirements and some of the early results in our MEMS-based raster correction scanner development effort. Since then, a lot of progress was made and the scanner was successfully incorporated into an SXGA resolution helmet-mounted display system. In this paper we report the results of thick copper coil development, new coil and magnet design for electromagnetic actuator, thermal flatness testing, new mounting design, and finally the performance measurements for the HMD system with a raster correction scanner.
Techniques and formulas will be presented that demonstrate an effective means of characterizing the rigid body motions of optical elements from their nominal positions as caused by manufacturing tolerances and thermal effects. These techniques allow accurate prediction of the final position of a mechanically held lens element to be determined relative to mechanical datums. Even a single lens element with entirely nominal dimensions often needs to be positioned relative to a mechanical reference; the effects of any inherent inaccuracy of the mounting process can be over-looked and/or oversimplified. Tolerances on lens seats, element radii, bore diameters as well as thermal effects need to be accounted for in a design in order to accurately predict the final optical performance of a system in an "as built" condition. The differences in accounting for the mounting tolerances of edge mounted, cell mounted, and surface-centered elements are discussed. The work presented will aid in linking the tools available to the optical engineer in the form of optical design software, with the data available to the mechanical engineer in the form of manufacturing and fabrication tolerances.
High-resolution (i.e., large pixel-count) and high frame rate dynamic microdisplays can be implemented by scanning a photon beam in a raster format across the viewer's retina. A resonant horizontal scanner and a linearly driven vertical scanner can create a 2-D raster for video display. The combined motion of the two scanners form a sinusoidal raster in the vertical direction and cause non-uniform line spacing for the case of bidirectional scanning as if the forward and return half-period raster lines are "pinched" near the edge of the display screen. 'Raster pinch" effect degrades the image quality, especially for multi-beam scanning systems. What is needed is a vertical scanner that creates a stairstep motion instead of linear motion. A third scanner can be added to the system to create an approximation to a staircase motion in the vertical axis and correct for the non-uniform raster spacing. The raster pinch scanner requirements, mechanical and magnetic designs with FEA analysis, and preliminary test results are discussed in this paper.
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