A typical flight control system utilizes control surfaces to control flight direction. In the case of a missile, fins typically provide these control surfaces. In general, movable fins attach to movable shafts which extend from the body of the missile. These fins move in various directions in response to movement of these shafts to control flight.
Manufacturers typically provide devices which lock the fins in place prior to missile launch. Such locking devices hold the fins in rigid and stable positions in order to prevent wear and tear on the drive mechanisms responsible for operating the fin shafts. For example, in the context of a missile positioned on the exterior of an aircraft, the fins of the missile are subjected to high aerodynamic loading prior to launch. Without the use of such locking devices, there is a greater likelihood that such loading will cause distortion and fatigue failures of the drive systems (e.g., motors, crank arms, drive trains, etc.) which are responsible for moving the fin shafts.
One conventional locking device includes, for each movable fin, a pin which locks into a crank arm configured to operate that fin. When the missile is launched (e.g., from an aircraft), the pins retract from the crank arms thus allowing the crank arms to move the fins. To assemble a missile with these conventional locking devices, the manufacturer typically selects and installs pins for locking the fins so that the fins reside as close as possible to their neutral (or ideal) positions for minimal friction and wear, and for high accuracy. In particular, a technician manually choose among multiple pins having different predefined offset ends, and a pin having a particular offset may work for one fin but not all fins of the same missile due to differences in tolerance stack up at each fin. In one conventional situation, the manufacturer provides the technician with a wide assortment of different pins to choose from (e.g., 10 different pins) with each pin having a slightly greater incremental offset.
Unfortunately, there are deficiencies to the above-described missile assembly approach which involves a technician selecting and installing pins by hand for use in locking missile fins in place prior to launch. For example, the above-described conventional approach often involves the technician using a trial and error, best-fit scheme which is extremely time consuming and inefficient. That is, if one pin having a particular offset does not hold a fin in its neutral position, the technician removes that pin and tries another pin having a different offset. The technician continues this process until the technician finds a suitable pin.
Additionally, the above-described conventional approach requires that the manufacturer provide an assortment of pins having different offsets. This creates an inventory burden on the manufacturer since not all of the pins will be used. Moreover, since selection of the pins is determined during time of assembly, the manufacturer is not able to accurately and reliably forecast the pins that will be used. Accordingly, the manufacturer is discouraged from pre-ordering or making the pins in larger, more-efficient quantities.
Furthermore, the above-described conventional best-fit scheme still poses the potential for imprecise pin installations. For example, there may be a situation where the predefined incremental offsets are too coarse to accommodate a particular fin thus leaving the fin slightly off from its neutral position. In such a situation, the aerodynamic loading on that fin may result in flutter or fatigue failure.
In contrast to the above-described conventional approach to assembling a missile which involves a technician employing a best-fit scheme for installing pins having predefined offsets, embodiments of the invention are directed to techniques for controlling a fin by utilizing an adjustable locking member which is configured to move from an engaged position to a disengaged position relative to an arm that couples to the fin. The locking member has a cylindrical body portion and a cylindrical end portion, which is eccentric with the cylindrical body portion, to enable the locking member (e.g., using rotational adjustments) to lock the arm in a substantially fixed state while the arm holds the fin in a neutral location. Such a locking member provides virtually unlimited adjustment capability to eliminate backlash between the locking member and the arm, and alleviates the need for a manufacturer to provide an assortment of pins having different predefined offsets.
One embodiment of the invention is directed to a fin control assembly which includes a housing, an arm configured to couple to a fin and to steer the fin relative to the housing, and a locking member disposed within the housing. The locking member is configured to move from an engaged position to a disengaged position relative to the arm. In particular, the locking member locks the arm in a substantially fixed state to inhibit movement of the arm relative to the housing when the locking member is in the engaged position. Additionally, the locking member unlocks the arm from the substantially fixed state to allow the arm to steer the fin relative to the housing when the locking member moves from the engaged position to the disengaged position. The locking member has a cylindrical body portion and a cylindrical end portion, which is eccentric with the cylindrical body portion, to enable the locking member to lock the arm in the substantially fixed state while the arm holds the fin in a neutral location. In one arrangement, rotation of the cylindrical body portion enables precise alignment of the arm to the proper fin neutral location. Accordingly, such an assembly enables precise arm control (i.e., robust and reliable fin-shaft locating) with unlimited adjustment and no backlash.
The foregoing and other objects, features and advantages of the invention will be apparent from the following description of particular embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Embodiments of the invention are directed to techniques for controlling a fin by utilizing an adjustable locking member which is configured to move from an engaged position to a disengaged position relative to an arm that couples to the fin. The locking member has a cylindrical body portion and a cylindrical end portion, which is eccentric with the cylindrical body portion, to enable the locking member (e.g., by making rotational adjustments) to lock the arm in a substantially fixed state while the arm holds the fin in a neutral location. Such a locking member provides virtually unlimited adjustment capability to eliminate backlash between the locking member and the arm, and alleviates the need for a manufacturer to provide an assortment of pins having different predefined offsets.
By way of example, the projectile device 20 is a missile which affixes to the exterior of an aircraft. In this example, the fins 24 are disposed 90 degrees apart around the circumference of the missile. Although four fins 24 are shown, it should be understood that a lesser or greater number may be utilized depending upon the particular type of projectile device 20 and its mission. Missiles for applications similar to that explained above are described in U.S. Pat. Nos. 6,250,584 and 6,352,217, the teachings of which are hereby incorporated by reference in their entirety. Further details of the invention will now be provided with reference to
The fin control assembly 26 further includes a control piston 48, a nut 50, packing 52, a pre-loaded spring 54, a retaining washer 56, a retaining ring 58, a locking wire 60, and a spring cap 62. The housing 42 defines a chamber 64 within which these components reside. The chamber 64 has an installation end 66 and an arm end 68. The housing 42 further defines a fluid port 70 which connects to the chamber 64. Further details of these components and their operation will be provided later.
It should be understood that the locking member 26 includes a body portion 72 and an end portion 74 which is integral with the body portion 72, i.e., as a solid, unitary element. The control piston 48 holds the body portion 72 so that both the control piston 48 and the body portion 72 move together along the Y-axis. The end portion 74 defines a tooth and is configured to engage with and disengage from a notched portion 76 of the arm 44. Further details of how the end portion 74 engages the notched portion 76 of the arm 44 will now be provided with reference to
At this point, it should be understood that the arm 44 has a fin neutral location 84 in which the fin 24 coupled to the arm 44 lies in an optimal orientation to the projectile body 22 (
As further shown in
During installation, the manufacturer has the capability of rotating the locking member 46 within the control piston 48. Moreover, such rotation is capable of occurring while the locking member 46 and the control piston 48 reside within the chamber 64 (
It should be understood that the locking member 46 is capable of rotating fully within the control piston 48. Accordingly, rotating the locking member 46 over 180 degrees from the orientation shown in
It should be further understood that the combination of the locking member 46 and the control piston 48 provides a continuous (rather than segmented) range of travel. Accordingly, each installation will have precise alignment with the fin neutral location 84 of the arm 44 (
It should be understood that the locking member 46 and the control piston 48 are initially disposed in the engaged position relative to the arm 44 as shown in
To operate the fin control assembly 26, highly pressurized fluid (e.g., either gas or liquid under 300 PSI) enters through the fluid port 70 and provides force in the opposite direction to that of the force provided by the spring 54. There is only low friction between the control piston 48 and the housing 42, e.g., due to a minute amount of friction provided by the packing 52 which provides a pressure seal between the control piston 48 and the housing 42 and due to the absence of any scraper. Accordingly, as soon as the force from the fluid exceeds the spring force, the control piston 48 quickly moves away from the arm 44 in the negative Y-direction and into the disengaged position as shown in
As the control piston 48 moves away from the arm 44, the retaining ring 58 captures the end of the control piston 48 (
As mentioned above, embodiments of the invention are directed to techniques for controlling a fin 24 by utilizing an adjustable locking member 26 which is configured to move from an engaged position (
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
For example, the projectile device 20 was described above as being a missile by way of example only. It should be understood that, in other arrangements, the projectile device 20 is a device other that a missile such as an aircraft or watercraft which requires fins 24 to be held in a stationary position prior to operation.
It should be further understood that the fin control assembly 24 is well-suited for an assembly test procedure in which a relatively small force is applied to the control piston 48 to move the locking member 46 out of engagement with the arm 44. By setting the magnitude of the force to be substantially smaller than that provided by the high pressure fluid, and due to the location of the retaining ring 58 at the end 66 of the chamber 64, the control piston 48 will have a short stroke and thus not be captured by the retaining ring 58 during testing. Such enhancements and modifications are intended to belong to various embodiments of the invention.
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