Abstract:
A passive caging system for use in gyro-stabilized sensor platforms and the like, employing a pneumatic dashpot in place of automatic caging gyro brakes, pin-locking devices, springs, fluid damped pistons, or air bladders. A pneumatic dashpot in combination with a normally closed solenoid valve provides effective damping of shock forces while the system is in the unpowered state. When power is applied to the system, the solenoid valve is open and unrestricted movement of the sensor platform is enabled.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/166,865, filed Nov. 22, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to gyro caging systems and, more particularly, to a passive caging system for use in gyro-stabilized sensor platforms and similar systems. 
     In the gyro-stabilized sensor platform field, it is essential that the system design adequately protect the delicate instruments of the sensor platform. The gyro-stabilized sensor platform must be protected from excessive shock forces. Currently, such protective measures operate only when the system is powered. In the unpowered state these protective measures are not active and are therefore unable to provide the necessary protection. The present invention provides the required degree of protection while the system is in the unpowered state, without requiring manual intervention or complex system design. 
     2. Description of Related Art 
     With gyro-stabilized sensor platforms, motors are frequently employed to actively damp gimbal, and therefore sensor platform, motion. These motors, when powered and active, may enable the gimbal unit to survive shock forces in excess of 20 times the force of gravity. An unfortunate consequence of these motor-damped gimbal systems is their inherent dependence upon power. When power to the motors is shut off, the protection offered by the motors is no longer present. As a result, it is not uncommon for gyro-stabilized gimbal and sensor platform systems to experience failures from shocks and other forces incurred during shipping, handling, and transport by the intended platform vehicle. 
     Various attempts have been made to prevent shock-related damage and failure of gyro-stabilized gimbal devices while in the unpowered state. A variety of pin-locking devices have been used with partial success. Such pin-locking devices, sometimes controlled by solenoids, serve to lock the inner gimbal frames to the gimbal package when the system is unpowered. These devices have the disadvantage that, through their operation and design, the majority of shock is transferred to the delicate and often expensive inner components, frequently resulting in their damage. 
     Attempts have been made to incorporate springs or fluid-damped pistons to resolve the problem. Unfortunately, these approaches tend to impair the sensitivity and response time of the gimbal platform. Still other attempts have employed air bladders to protect the gimbal devices. These air bladders frequently require manual intervention of a sensor platform user. They also require that the system design provide an air pump and its attendant electronics. 
     Fluid dashpots have been used in conjunction with gyro-stabilized platforms to preclude gyro precession angles in excess of design range. By employing linkages between the gyro rotor housing and a fluid dashpot, the disclosed assembly of U.S. Pat. No. 4,193,308 of Stuhler et al. permits unimpeded precession motion over a design range of precession angles while providing caging capabilities to prevent extreme motion states in excess of normal gyro design limits. 
     U.S. Pat. No. 4,016,960 of Wilcox discloses a dashpot with a guided piston which limits motion of the piston within a cylinder along a particular axis. U.S. Pat. No. 3,939,947 of Cohen, et al. discloses a dashpot for selectively directed damping of applied forces. The dashpot includes a cylinder, a piston which is sealingly slidable within the cylinder, and a piston rod which drives the piston. Various valve members which are connected into the system establish the direction of the damping force. 
     U.S. Pat. No. 4,322,984 of Lasker et al. discloses a gyroscope caging system having a clamping ring which encircles a portion of the gyro rotor. The clamping ring is adapted to engage an annular groove in the rotor simultaneously with engagement of a groove in a base support member for clamping the rotor during very high acceleration launches of a missile or airborne vehicle. However, it depends upon being actively powered for its operation and cannot perform its clamping function in the absence of power. 
     U.S. Pat. No. 3,992,955 of Evans et al. discloses a caging mechanism for a gyro in which a flat split ring mounted in a plane perpendicular to the gyro rotor spin axis is deformable to capture the gyro rotor when deformed by a gas activated piston. When the piston is operative, the rotor is either caged or uncaged depending upon the state of the deformable split ring. 
     U.S. Pat. No. 4,807,485 of Bennett discloses a motor driven caging system for a free gyro which cages both the inner and out gimbals thereof and locks in both the caging and uncaging positions by means of an over-center mechanism. While this system locks in both the caging and uncaging positions, it is not clear what position will be maintained when the system is not powered. 
     While it is generally recognized that dashpot and linkage systems may provide a damping function to restrict gyro precession beyond design limits, the complex nature of such arrangements increases both material and production costs and adds unnecessary complexity to the system. Further, such damping systems function only while the system is in its powered state. None of the cited prior art discloses the novel features of the present invention which provides gyro platform dampening in the unpowered state. 
     The present invention provides a passive damping system which operates in the unpowered state of gyro-stabilized platforms and similar systems. Further, the present invention becomes functionally transparent during powered operation of the system. In other words, the damping device is operative only when power to the system is off. Embodiments of the invention may have applications for both closed and open loop gyro systems, as well as in numerous other systems which utilize gimbals to position or isolate delicate instruments and electronics. 
     SUMMARY OF THE INVENTION 
     In brief, particular arrangements of the present invention involve the provision of a pneumatic caging system for gyro-stabilized sensor platforms. Such gyro-stabilized platforms are frequently employed in the stabilization of certain sensors. One arrangement in accordance with the present invention provides secure caging of an unpowered gyro-stabilized platform through use of a dashpot assembly comprising a pneumatic dashpot in combination with a normally closed solenoid valve. The solenoid is connected to system power. The associated valve is connected in the pneumatic feedback loop. When the system is in its unpowered state, the deactivated solenoid maintains the valve in the closed position. When the piston of the dashpot is confined by the air pressure maintained by the closed solenoid valve, it functions as an equal-force, bidirectional spring. In this manner, effective damping of shock forces is achieved. 
     When power is applied to the solenoid, the pneumatic valve is opened and unrestricted movement of the dashpot piston is permitted. Accordingly, the gyro-stabilized sensor platform which is connected to the dashpot piston is permitted full and free operation. 
     The incorporation of a pneumatic dashpot and normally closed solenoid valve design rather than pin-locking devices, springs, fluid-damped pistons, or air bladders, provides effective and inexpensive protection of gyro-stabilized sensor platforms. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention may be realized from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a schematic perspective view of a pneumatic caging system according to a preferred embodiment of the invention; 
     FIG. 2 is a side elevational view of the pneumatic caging system of FIG. 1; 
     FIG. 3 is a schematic plan view of a single port dashpot assembly for inclusion in the system of FIGS. 1 and 2; and 
     FIG. 4 is a schematic plan view of a dual port dashpot assembly for inclusion in the system of FIGS.  1  and  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 and 2 show the portion of an overall gyro-stabilized sensor platform system which comprises a particular arrangement of the present invention. As shown in FIG. 1, the pneumatic caging system  10  of the present invention comprises a gimbal payload  12  to which are secured solenoid housing  22  and dashpot housing  32 . Extending through solenoid housing  22  are air passages from solenoid ports  24 . Extending through dashpot housing  32  are passages from dashpot ports  42 ,  44 . Dashpot ports  42 ,  44  and solenoid ports  24  may be adapted to receive interconnecting tubing (not shown) or to vent to atmosphere. Connecting shafts  38  extend from dashpot housing  32  and terminate in attachment points  40 . Gimbal axis extension  16  is secured to and extends between gimbal payload  12  and attachment points  40  of connecting shafts  38 . Connecting shafts  38  may move linearly over a prescribed distance along parallel axes. Attachment point  40  of each connecting shaft  38  may be pivotably secured via gimbal axis extension  16  to inner gimbal axis  14 . 
     The gimbal of FIGS. 1 and 2 is shown with a dual-dashpot implementation. Particular details of the dashpot stabilizing mechanism are omitted for simplification. When a gyro-stabilized gimbal platform is operated, the standard gimbal control system (open or closed loop) works to keep the gimbal platforms centered within their hard stops. The arrangements of the present invention become effective as power is shut off from such a unit in order to maintain protection of the sensitive components of the system. 
     In the embodiment of the invention shown in the schematic diagram of FIG. 3, dashpot assembly  30  comprises piston  34  having connecting shaft  38  extending from one side thereof and contained within cylinder  36 . Connecting shaft  38  terminates in attachment point  40  at the end of connecting shaft  38  opposite piston  34 . Cylinder  36  is closed at one end, most commonly on the side of piston  34  opposite connecting shaft  38 , creating a chamber having variable volume depending upon movement of piston  34  relative to cylinder  36 . As piston  34  moves relative to cylinder  36  and the volume contained in cylinder  36  is varied, pneumatic exchange occurs through dashpot port  42 . 
     Connecting shaft  38  is secured to one side of piston  34  contained by cylinder  36 . The movement of piston  34  and connecting shaft  38  relative to cylinder  36  and thereby gimbal payload  12  is controllable by pneumatic exchange through dashpot port  42  which in turn is controlled by solenoid valve  20 , which is electrically connected to system power  18 . When solenoid valve  20  is opened, which occurs when power is applied to the unit, unrestricted pneumatic exchange may occur through solenoid valve  20 . In this case, movement of piston  34  relative to cylinder  36  is similarly unrestricted. 
     This pneumatic exchange may be controlled by solenoid valve  20 . When in the open position, solenoid valve  20  permits the unimpeded pneumatic exchange through dashpot port  42 . Accordingly movement of piston  34  relative to cylinder  36  is similarly unimpeded. 
     When solenoid valve  20  is closed, as when the solenoid is not energized due to removal of system power  18 , air flow is blocked by solenoid valve  20  and thereby the movement of piston  34  relative to cylinder  36  is restricted. In this condition, piston  34  and cylinder  36  function as a bi-directional resilient spring force. The dashpot of FIG. 3 is provided with a single port  42  which communicates via the solenoid valve  20  with atmosphere. 
     The embodiment of the invention depicted in FIG. 4 incorporates a closed loop system. This has two ports  42  and  44  on opposite sides of the piston  34  and is appropriate for use in a corrosive environment. In this embodiment, cylinder  36 ′ is closed at both ends on opposite sides of the piston  34 . The solenoid valve  20  is connected in series between the two dashpot ports  42 ,  44 . A second dashpot port  44  is located on the opposite side of piston  34  from dashpot port  42 . Solenoid valve  20  is in series between dashpot ports  42  and  44 . 
     When solenoid valve  20  is open, unimpeded pneumatic exchange may occur through the dashpot ports  42 ,  44  and thus unrestricted movement of piston  34  relative to cylinder  36 ′ is permitted. When solenoid is not supplied with power, valve  20  is closed, pneumatic exchange is prevented and thereby piston  34  is restrained within cylinder  36 ′. In this case, piston  34  functions as a bi-directional, resilient spring force, as in FIG.  3 . 
     By securing gimbal axis  14  or gimbal payload  12  to attachment point  40  of connecting shaft  38  and the other element to cylinder  36 , movement of gimbal payload  12  relative to inner gimbal axis  14  may be controlled. By employing the normally closed solenoid valve  20 , pneumatic flow through solenoid valve  20  is prevented when the solenoid is without power, and thus movement of piston  34  relative to cylinder  36  is restricted. By restricting piston  34  within cylinder  36 , through the closure of solenoid valve  20 , shock forces applied to one of either gimbal payload  12  or inner gimbal axis  14  may be significantly damped. 
     When power is applied to normally closed solenoid valve  20 , the valve is opened and pneumatic exchange may occur. With solenoid valve  20  opened, piston  34  is free to move relative to cylinder  36 . Thus, gimbal payload  12  may move independently and unrestricted by movement of inner gimbal axis  14 . 
     Although there have been described hereinabove various specific arrangements of a PNEUMATIC CAGING SYSTEM FOR GYRO-STABILIZED SENSOR PLATFORMS in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention as defined in the annexed claims.