Abstract:
A spin control system includes first and second thrusters coupled to an object hanging from a suspension member. When activated, the first and second thrusters generate thrust in opposing directions that are substantially perpendicular to the longitudinal axis of the suspension member. When the object spins, a controller activates at least one of the first and second thrusters to approximately align the object with a reference position.

Description:
ORIGIN OF THE INVENTION 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to control of suspended objects, and more particularly to a system that can control the spin of an object suspended from a non-rigid suspension member. 
     BACKGROUND OF THE INVENTION 
     Objects suspended in air by a rope, cable or any other non-rigid suspension member, have a tendency to spin about the longitudinal axis of the suspension member. Such “objects” can be those deployed/recovered from the water (e.g., an underwater vehicle, a person being rescued from the water by helicopter, etc.) or can be those conveyed on the land (e.g., a crane lifting a load for high-rise construction purposes). In either case, the spin of the suspended object can cause handling difficulties or hazardous conditions. Accordingly, when possible, a tag-line coupled to the suspended object is used by a ground-based person to prevent spin. However, suspended-object scenarios taking place over open water or on high-rises do not lend themselves to the use of tag-lines. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a spin control system for suspended objects. 
     Another object of the present invention is to provide a self-contained system that can control the spinning of an object suspended in air by a non-rigid suspension member. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, a spin control system for a suspended object includes first and second thrusters. The first thruster is coupled to an object hanging from a suspension member. When activated, the first thruster generates thrust in a first direction that is substantially perpendicular to the longitudinal axis of the suspension member. The second thruster is also coupled to the object and is adjacent to the first thruster. When activated, the second thruster generates thrust in a second direction that is opposite the first direction while also being substantially perpendicular to the longitudinal axis of the suspension member. When the object spins, a controller activates at least one of the first and second thrusters to approximately align the object with a reference position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
         FIG. 1  is a schematic plan view of a suspended-object spin control system in accordance with the present invention; 
         FIG. 2  is a perspective view of a self-contained, suspended-object spin control system coupled to a suspended object in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic plan view of a suspended-object spin control system configured for an underwater vehicle recovery scenario in accordance with another object of the present invention; and 
         FIG. 4  is a schematic plan view of a suspended-object spin control central system that includes wireless control communication and proximity sensors in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to  FIG. 1 , a spin control system in accordance with the present invention is shown and is referenced generally by numeral  10 . Spin control system  10  is to be coupled to an object (not shown in  FIG. 1 ) that is suspended in air by means of a non-rigid suspension member (e.g., rope, line, cable, etc.). As would be understood in the art, an object so-suspended will have a tendency to spin about the longitudinal axis of the suspension member. Such spinning can be caused by one or more of weight imbalances of the object relative to the longitudinal axis of the suspension member, wind, slewing movement of the object, etc. 
     In general, the present invention uses two or more thrusters to counteract the spin of a suspended object. At a minimum, spin control system  10  includes a first thruster  12 , a second thruster  14 , a thruster controller  16 , and a position/orientation sensor  18 . For example, in the illustrated embodiment, thrusters  12  and  14  are positioned such that the thrust force generated by an activated thruster  12  is directed in a direction  13  that is opposite that of direction  15 , i.e., the direction of the thrust force generated by an activated thruster  14 . The activation of one or both of thrusters  12  and  14  is controlled by thruster controller  16 . Position/orientation sensor  18  detects either a position or orientation of system  10  and provides same to thruster controller  16 . Since system  10  is coupled to the suspended object, the position/orientation information detected by sensor  18  provides position/orientation information about the suspended object. Controller  16  uses the position/orientation information to activate/deactivate thrusters  12  and/or  14 . Although not shown, it is to be understood that system  10  will typically include an onboard power source for powering the above-described components. 
     To provide a clearer understanding of the present invention, an embodiment thereof will be explained with additional reference to  FIG. 2 . In  FIG. 2 , the illustrated embodiment of system  10  is coupled to an outboard end  100 A of an object  100  that is suspended in air by means of non-rigid suspension member  200  that extends up to a support (not shown) such as a winch, crane, etc., the choice of which is not a limitation of the present invention. The weight of object  100  causes suspension member  200  to be placed in tension along the longitudinal axis  202  thereof. As is well known in the art, this scenario will tend to cause object  100  to spin about longitudinal axis  202  as indicated by two-headed rotational arrow  204 . 
     In the illustrated embodiment, system  10  has a housing  20  that is coupled to outboard end  100 A of object  100 . Such coupling can be permanent (e.g., bolted) or temporary (e.g., magnetic) without departing from the scope of the present invention. Housing  20  contains and protects the various electronics components (e.g., controller  16 , sensor  18 , power source, etc.) of system  10  that are not shown in  FIG. 2  to maintain clarity of illustration. 
     Mounted to housing  20  or integrated with housing  20  is a mounting support  22  for each of thrusters  12  and  14  which can be, for example, ducted fans. In the illustrated embodiment, housing  20 /support  22  fixes the positions of thrusters  12  and  14  adjacent to one another with respective thrust directions  13  and  15  pointing in opposite directions. Housing  20 /support  22  is configured and/or coupled to object  100  such that thrust directions  13  and  15  are substantially perpendicular to longitudinal axis  202  while lying in a plane that is substantially parallel to longitudinal axis  202 . In this way, thrusters  12  and  14  can be controlled to counter spin  204 . The greater the separation distance between longitudinal axis  202  and thrusters  12 / 14 , the lower the force required to control spin  204 . 
     In order to “know” which of thrusters  12  and  14  needs to be activated to counter spin  204 , controller  16  needs a reference position or orientation. Depending on the application, such reference information can be predetermined/stored by controller  16 , manually or remotely entered into controller  16  at time of use, or determined in-situ by system  10 , without departing from the scope of the present invention. For example, an in-situ determination of position/orientation could be used in an embodiment of the present invention configured for an underwater recovery operation as illustrated in  FIG. 3  where like reference numerals are used for the elements described earlier herein. 
     The system illustrated in  FIG. 3  can be used when an underwater vehicle (not shown) is being recovered from an in-air location (e.g., on a dock/platform, onboard a ship, from a helicopter, etc.). Typically, the underwater vehicle will be positioned in a desired orientation or heading just prior to recovery from the water. Accordingly, a depth sensor  30  can be used to supply a system activation signal to controller  16  and/or sensor  18  when a prescribed depth just below the water&#39;s surface is detected. It is to be assumed that the underwater vehicle is in its desired orientation for recovery at this depth. Accordingly, at this depth, the position/orientation detected by sensor  18  is used by controller  16  as the reference position that will govern the control of thrusters  12  and  14  as described above. 
     Since thrusters  12  and  14  will typically only be capable of in-air operation, the present invention&#39;s spin control will actually be implemented only after the underwater vehicle clears the water and is suspended by the recovery line. To insure this operational scenario, a water or air sensor  32  is used. The signal produced by sensor  32  can either be used to inhibit or enable thruster operation so that thrusters  12  and  14  are only activated in the air. 
     While the present invention can be configured as a completely self-contained system, other embodiments thereof are possible without departing from the scope of the present invention. For example,  FIG. 4  illustrates another embodiment of the present invention where the system shown in  FIG. 1  is further configured for wireless communication. More specifically, a wireless receiver  40  is coupled to controller  16  and a wireless transmitter  42  is provided for use at a remote location. Receiver  40 /transmitter  42  can be configured to simply provide activation/deactivation of the spin control system, or can be configured to provide programming for controller  16 . In addition, proximity sensor(s)  50  could be included and used to detect obstacles. The obstacle detection information could be provided to controller  16  so that thrusters  12  and  14  could be activated for autonomous obstacle avoidance. 
     The advantages of the present invention are numerous. Handling difficulties and/or dangerous conditions created by spinning suspended objects are eliminated by a simple, self-contained system. The present invention can be permanently attached/integrated into an object, or can simply be attached thereto when needed. 
     Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. For example, three or more thrusters could be used to enhance spin control as the thrust direction(s) of the additional thruster(s) would be directed to increase the degrees of freedom of the control movements. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.