Patent
1989-04-10
1991-05-21
Arnold, Bruce Y.
350607, G02B 510, G02B 718
Patent
active
050169980
ABSTRACT:
A focus control system dynamically sets and controls the focal length of a reflective membrane supported between a perimeter frame. A rear membrane is also supported between the perimeter frame rearward and spaced apart from a back side of the reflective membrane. The space between the membranes defines a plenum space into which a mass of gas at a first pressure is inserted. The pressure differential between the first pressure and an external pressure, such as the atmospheric pressure, causes the reflective membrane to assume a first curvature relative to a reference plane associated with the perimeter frame. This curvature defines the focal length of the reflective membrane. The focal length is dynamically controlled by changing the volume of the plenum space, thereby changing the first pressure. The system can be used to change or maintain the pressure differential and hence the front membrane curvature. The plenum volume is changed by pushing or pulling on a central section of the rear membrane using a suitable actuator. Sensing means continuously sense the location of the reflective membrane relative to the reference plane. This sensed position is compared to a reference position, and a resulting error signal, comprising the difference between the sensed position and reference position, drives the actuator in a direction to minimize the difference. A vent value compensates for temperature changes or leaks in the closed volume by allowing the pressure differential to be adjusted as required to center the working range of the actuator about the desired focal length.
REFERENCES:
patent: 4179193 (1979-12-01), Gillette et al.
patent: 4422723 (1983-12-01), Williams et al.
patent: 4511215 (1985-04-01), Butler
Murphy, L. M., "Technical and Cost Benefits of Lightweight Stretched-Membrane Heliostats", SERI/TR-253-1818, Technical Report Prepared Under Contract No. EG-77-C-01-4042, Solar Energy Research Institute, Golden, Colo. (May 1983).
Murphy, L. M., "Stretched-Membrane Heliostat Technology", J. of Solar Engineering, vol. 108, pp. 230-238 (Aug. 1986).
"Development of the Stressed Membrane Heliostat", SAND87-8180, Contractor Report, Sandia National Laboratories, Albuquerque, N.M. (Apr. 1987).
Butler et al., "Development of Stressed Membrane Heliostat Mirror Module", SAIC 86/1872, Final Report, Science Applications International Corporation (Nov. 1986).
Beninga Kelly J.
Butler Barry L.
Arnold Bruce Y.
Phan James
Science Applications International Corporation
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