1. Field of the Invention
The present invention relates generally to optical systems, and more specifically to an assembly that flexurally suspends a mirror to reflect millimeter wave energy to a radiometer.
2. Description of the Prior Art
Mirrors are often used in imaging systems to direct electromagnetic radiation for various applications such as lasers, x-rays, and thermal imaging. There are static type mirrors that are fixed permanently into position. This type of static system has been used with aircraft performing reconnaissance over a designated area. The mirror on the aircraft is fixed so that the aircraft is required to maneuver to focus the mirror on a larger area to complete a survey. This is a shortcoming in functionality that has been addressed with another type of mirror system that has the ability to be adjusted and rotated about an axis or axes.
Both aircraft and satellite cameras have used flexurally suspended mirrors for decades. They generally move about only one axis.
The scanning mechanism that is the subject of this invention uses a flexurally suspended mirror in a millimeter wave imaging system. A millimeter wave imaging system uses either active or passive detection and measurement of electromagnetic radiation at millimeter wavelengths. The contrast in radiation between the surrounding background environment and individual undergoing a scan identifies concealed objects under clothing.
In an adjustable mirror system, the mirror is used to scan the imaging zone and redirect millimeter wave energy to the focal plane of a lens. This reduces the required size of the radiometer. The mirror is mounted on a universal joint about two perpendicular axes. The universal joint provides the pivot point as actuators position the mirror as desired. However, this type of prior art system is not suited for scanning at a rapid rate. Furthermore, the universal joint is susceptible to failure and vibration as it becomes worn from use.
To overcome the failure of universal joints, the prior art describes an alternative mirror mount whereby a rod and flexible neck serve as a substitute for a universal joint to support the mirror. Actuators are used to tilt the mirror about the flexible neck and a diaphragm secures the mirror to the support body. However, a shortcoming of this type of system is the small field of scanning of less than 1 degree.
Accordingly, there is a need for a mirror scanning system that has the ability to scan a large field of view.
There is also a need in the art for an improved mirror scanning system that is accurate and not susceptible to wear of the assembly after normal operation.
It is, therefore, to the effective resolution of the aforementioned problems and shortcomings of the prior art that the present invention is directed.
However, in view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The invention provides for a mirror scanning system with a mirror held substantially rigid in four degrees of freedom by two flexures, which permits rotation about the two remaining degrees of freedom. The mirror may be made of a honeycomb type material for lightness with rigidity. The system includes a pair of voice coil actuators aligned generally perpendicular to a mirror; a pair of corresponding cylinders secured to a center yoke, or moving coil bobbin, of each of the respective voice coil actuators; the pair of voice coil actuators having a circular flange disposed upon the periphery of the cylinders wherein the cylinders may be moved substantially axially by electrical current driven through the voice coil actuators by external amplifiers. Each cylinder is attached to a point on the mirror near its periphery by an actuator rod flexture, and drives the mirror to rotate about one of a pair of mutually perpendicular axes; and a base supporting a back plate generally disposed parallel to the mirror which mounts the voice coil actuators. The millimeter wave energy from an imaging zone is reflected by the mirror scanning system of the present invention to a radiometer. The millimeter wave energy is then processed to produce contrast-based images.
The specific embodiments described above provide an improved mirror scanning system that overcomes the limitations of the prior art.
A primary object of the invention is to provide lower fabrication costs of a mirror scanning system.
Another very important object of the invention is to provide a mirror scanning system that has the ability to scan a large field of view.
Still another important object of the invention is to provide an improved mirror scanning system that is accurate and not susceptible to wear of the assembly after normal operation.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.
For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
Referring to
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A position sensor 190 is mounted to each sensor bracket 230, which is adjacent to each cylinder of pair of cylinders 120. Sensor 190 is used to determine precisely the axial positions of cylinders 120 and actuator rod flexures 160 and hence the angles of mirror 150. In the preferred embodiment, sensor 190 is a high-resolution glass scale position sensor. Scale 240 is mounted to cylinder 120 so that sensor 190 can determine the position of cylinder 120. In alternative embodiments, sensor 190 is a low-resolution metal scale sensor or a photo-reflective limit switch.
The lower portion of front coil flexure 170 is attached to the front portion of base 140. Similar to rear coil flexure 175, front coil flexure 170 comprises a matching pair of apertures disposed at the apex of each triangular member. The pair of apertures allows a continuous path for pair of rod flexures between the pair of corresponding voice coils and the mirror. As shown in
Referring now to
The particular embodiments disclosed above and in the drawings are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which as a matter of language, might be said to fall therebetween.