News Column

Patent Issued for Variable Aperture and Actuator Assemblies for an Imaging System

June 25, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- DRS RSTA, Inc. (Melbourne, FL) has been issued patent number 8746570, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Powell, Donald A. (Dallas, TX); Malarcher, Falvey L. (Plano, TX).

This patent was filed on June 10, 2013 and was published online on June 10, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Thermal infrared radiation (IR) is emitted from all objects as a function of their temperature. IR imaging systems are able to detect thermal signatures and identify target objects by analyzing the heat and profile emitted. The mid-wave and long-wave IR detectors used in IR imaging systems are typically housed in vacuum enclosures, commonly referred to as dewars, and cooled to cryogenic temperatures to improve target detectability and lower signal to noise ratios.

"A conventional IR imaging system 100 employing a typical dewar system 102 to cryogenically cool an infrared detector 104 is depicted in FIG. 1. The infrared detector 104 is mounted on a substrate 106 attached to a cold stem 108 of the dewar system 102. The cold stem 108 houses the refrigeration portion of a stirling cycle refrigerator which cools and maintains the detector 104 at cryogenic operating temperatures. The detector 104 is typically mounted within a coldshield 110 that is housed within a vacuum enclosure 112 of the dewar system 102. The vacuum enclosure 112 includes a window 114 attached to the top 116 of the vacuum enclosure 112 that allows the detector 104 to receive radiation signals external to the vacuum enclosure 112. The optics system of the IR imaging system 100 may be incorporated in the window 114 to the vacuum enclosure 112 or be positioned relative to the window 114 in the external housing (not shown in FIG. 1) of the IR imaging system 100.

"The coldshield 110 typically includes a fixed aperture 116 that essentially forms the f-stop for the optics system of the IR while also serving as a radiation shield for the detector. Some conventional IR imaging systems are capable of switching between narrow and wide field of view window or optics system (e.g., window 114 or the optics system disposed in the external housing of the IR imaging system 100) to view various target scenes, which requires two different coldshield aperture sizes to effectively match the optics system. A large family of dewars with coldshields of different aperture sizes is currently needed to accommodate the broad range of IR camera system designs. Hence, the need arises for a dewar to have a single coldshield with a variable aperture assembly having two or more apertures that may be switched on command to accommodate the various optical systems that may be employed in an IR imaging system. Moreover, there is a need for an aperture actuator or control means that does not generate a significant amount of heat within the vacuum enclosure when powered on to drive the variable aperture assembly.

"U.S. Pat. No. 7,157,706 to Gat et al. discloses variable aperture assemblies (each generally referenced as 122 in FIG. 1) for use in an IR camera having a dewar system 200 with a detector 104 mounted in a coldshield 110 that is enclosed in a vacuum chamber 112 as shown in FIG. 1. However, each non-magnetic driven variable aperture assembly 122 disclosed by Gat requires modifying the vacuum chamber 112 wall to either (1) add an external aperture control means 120, such as a worm gear system to drive a worm gear attached to the variable aperture assembly 122, or (2) to accommodate a piezoelectric motor aperture control means that directly contacts a friction surface of an outer drive ring of the variable aperture assembly 122. These conventional variable aperture assemblies and corresponding aperture control means are known to be extremely large in size (requiring significant space within the vacuum chamber or within the external housing of the IR imaging system) and require significant force and travel to control the size of the variable or swappable aperture to be used.

"Accordingly, there is a need for an improved variable aperture assembly and aperture actuator assembly that overcomes the problems noted above and others previously experienced for implementing a variable aperture and actuator within a dewar system of a cooled IR imaging system or camera."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "In accordance with systems consistent with the present invention, an imaging system is provided. The imaging system comprises a housing for a radiation detector (such as a cold shield housing), a variable aperture assembly, and an actuator assembly for the variable aperture. The radiation detector housing has a window disposed above and in axial alignment with the radiation detector. The variable aperture assembly includes a base ring having a first opening and mounted on the radiation detector housing such that the first opening is in axial alignment with the window of the radiation detector housing. The variable aperture assembly also includes a plate and at least one aperture blade (e.g., a single blade, two blades, or four blades) having a first aperture and adapted to engage the base ring such that the first aperture is disposed over the window. Each aperture blade is operatively coupled to the base ring so that the respective aperture blade is adapted to move laterally relative to the first aperture. The variable aperture further includes an aperture drive mechanism having a body and an actuator coupling member extending at an angle from the body. The body is operatively coupled to the base ring and to each aperture blade such that the aperture drive mechanism drives each aperture blade laterally away from the first aperture in response to the actuator coupling member being moved in a first lateral direction, and laterally over the first aperture to define a second aperture disposed over the window in response to the actuator coupling member being moved in a second lateral direction. The actuator assembly is disposed adjacent to the radiation detector housing in proximity to the actuator coupling member. The actuator assembly has an actuator and an actuator arm. The actuator arm has a first end operatively coupled to the actuator and a second end adapted to engage the actuator coupling member of the aperture drive mechanism so that the actuator controls the lateral movement of the actuator coupling member.

"In accordance with articles of manufacture consistent with the present invention, a variable aperture assembly for use in an imaging system having a housing for a radiation detector. The housing has a window disposed above and in axial alignment with the radiation detector. The variable aperture assembly comprises a base ring, a plate disposed over the base ring, at least one aperture blade, and an aperture drive mechanism. The base ring has a first opening and is adapted to be mounted on the radiation detector housing such that the first opening is in axial alignment with the window. The plate has a first aperture and is adapted to engage the base ring such that the first aperture is disposed over the window. Each aperture blade is operatively coupled to the base ring so that each aperture blade is adapted to move laterally relative to the first aperture. The aperture drive mechanism has a body and an actuator coupling member extending at an angle from the body. The body is operatively coupled to the base ring and to each aperture blade such that the aperture drive mechanism drives each aperture blade laterally away from the first aperture in response to the actuator coupling member being moved in a first lateral direction, and laterally over the first aperture to define a second aperture disposed over the window in response to the actuator coupling member being moved in a second lateral direction.

"In one implementation of the variable aperture assembly, the at least one aperture blade includes a first blade having a first end rotatably coupled at a pivot point to either the base ring or the plate, a second end adapted to be pivoted relative to the first end, and an inner portion disposed between the first and second ends. The inner portion defines the second aperture. The base ring or the plate to which the first blade is rotatably coupled has an upper surface, a first stop pin disposed on the upper surface away from the pivot point, and a second stop pin disposed on the upper surface across the first aperture from the first stop pin and substantially away from the pivot point. The first stop pin is adapted to engage the second end of the first blade to stop the lateral movement thereof when the first blade is moved laterally away from the first aperture so that the first aperture is exposed. The second stop pin is adapted to engage the second end of the first blade to stop the lateral movement thereof when the first blade is moved laterally over the first aperture so that the second aperture is disposed over the window.

"In another implementation of the variable aperture assembly, the base ring has an outer diameter defining an outer surface and a flange extending from the outer surface. In this implementation, the body of the aperture drive mechanism corresponds to a drive ring adapted to rotate about the base ring in sliding contact with the flange of the base ring. In addition, the base ring may have a plurality of pivot pins circumferentially spaced on the base ring. The drive ring may have a plurality of drive pins circumferentially spaced on the drive ring relative to the pivot pins. In this implementation, the at least one aperture blade corresponds to two or more aperture blades each having a first end and a second end. The first end of each blade has a pivot opening adapted to receive a respective one of the pivot pins and a drive opening adapted to receive a respective one of the drive pins such that the second end of the respective blade is adapted to pivot relative to the first end when the drive ring is rotated about the base ring.

"In another implementation of the variable aperture assembly, the drive ring has a plurality of stop pins circumferentially spaced on the drive ring such that each drive pin is disposed between a respective two of the stop pins. Each aperture blade has a top portion and a lower portion that collectively form a substantially L-shape having an external corner. The lower portion includes the first end and has an outer edge. The top portion includes the second end and has an external edge. The pivot opening and the drive opening of each aperture blade are disposed near the external corner. Each stop pin is adapted to engage the external edge of the top portion of a respective one of the aperture blades to stop the lateral movement thereof when the aperture blade is moved laterally away from the first aperture so that the first aperture is exposed. Each stop pin may also be adapted to engage the outer edge of the lower portion of a respective second of the aperture blades to stop the lateral movement thereof when the aperture blade is moved laterally over the first aperture so that the second aperture is disposed over the window.

"In another implementation of the variable aperture assembly, the plate has a circular outer edge that defines a rim along an outer perimeter of the base ring and the body of the aperture drive mechanism corresponds to a drive ring adapted to rotate about the outer edge of the plate in sliding contact with the rim of the base ring. The plate has a first plurality of guide pins circumferentially spaced on the plate. The drive ring has a plurality of drive pins circumferentially spaced on the drive ring relative to the guide pins. In this implementation, the at least one aperture blade corresponds to two or more aperture blades. Each aperture blade has a first guide pin track running in a direction substantially parallel to a corresponding radial axis of the window, and a drive pin track running in a direction substantially diagonal to the first guide pin track of the aperture blade. Each of the plurality of drive pins is operatively coupled to the drive pin track of a corresponding one of the aperture blades such that each drive pin travels along the drive pin track of the corresponding aperture blade in response to the drive ring being rotated about the outer edge of the plate. Each of the first plurality of guide pins is operatively coupled to the first guide pin track of a corresponding one of the aperture blades such that each first guide pin travels along the first guide pin track of the corresponding aperture blade in response to the drive pin traveling along the drive pin track of the corresponding aperture blade.

"In accordance with articles of manufacture consistent with the present invention, an aperture actuator assembly for use in actuating a variable aperture assembly disposed over a window of radiation detector housing in an imaging device is provided. The variable aperture assembly includes an aperture drive mechanism having a body and an actuator coupling member extending down at an angle from the body. The actuator coupling member is adapted to be moved in a first lateral direction so that the variable aperture assembly defines a first aperture over the window and in a second lateral direction so that the variable aperture assembly defines a second aperture over the window. The aperture actuator assembly comprises an actuator adapted to be disposed adjacent to the radiation detector housing below the actuator coupling member, and an actuator arm disposed between the actuator and the actuator coupling member. The actuator arm has a first end operatively coupled to the actuator and a second end adapted to engage the actuator coupling member of the aperture drive mechanism so that the actuator controls the lateral movement of the actuator coupling member.

"In one implementation of the aperture actuator assembly, the actuator is a piezoelectric motor having an actuator rod operatively coupled to the first end of the actuator arm and adapted to be selectively moved between a first position to cause the actuator arm to move in the first lateral direction and a second position to enable the actuator arm to move in the second lateral direction.

"In another implementation of the aperture actuator assembly, the aperture actuator assembly also includes a mounting bracket extending vertically relative to the radiation detector housing. The actuator arm is pivotally coupled to the mounting bracket such that the second end of the actuator arm is adapted to rotate in the first lateral direction and the second lateral direction. The actuator comprises a magnet and a voice coil motor having a wire coil operatively configured to receive a drive current. The wire coil is incorporated in the first end of the actuator arm and the magnet is disposed relative to the wire coil so that the magnet drives the first end of the actuator arm away from the magnet in a predetermined direction in response to the drive current flowing through the wire coil. The predetermined direction corresponds to one of the first lateral direction and the second lateral direction based on a direction of flow of the drive current through the wire coil.

"In another implementation of the aperture actuator assembly, the actuator assembly further comprises a mounting bracket extending vertically relative to the radiation detector housing. The actuator arm is pivotally coupled to the mounting bracket such that the second end of the actuator arm is adapted to rotate in the first lateral direction and the second lateral direction. The actuator comprises an electromagnetic solenoid having a drive input and a piston adapted to move along a longitudinal axis of the solenoid between an extended position and a contracted position based on the drive input. The piston has an end operatively coupled to the first end of the actuator arm so that the piston drives the second end of the actuator arm in the first lateral direction when moving towards the extended position and in the second lateral direction when moving towards the contracted position.

"Other systems, methods, features, and advantages of the present invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims."

For the URL and additional information on this patent, see: Powell, Donald A.; Malarcher, Falvey L.. Variable Aperture and Actuator Assemblies for an Imaging System. U.S. Patent Number 8746570, filed June 10, 2013, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8746570.PN.&OS=PN/8746570RS=PN/8746570

Keywords for this news article include: DRS RSTA Inc.

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Source: Journal of Engineering


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