Abstract:
A method and apparatus for use with a transfer system for transferring a trolley between first and second stations, the system including an inhaul winch, an outhaul winch, a cable and a trolley, the inhaul winch mounted to the first station, the outhaul winch mounted to one of the first and second stations, the cable extending between the first and second stations and between the inhaul and outhaul winches and the trolley mounted to the cable, the assembly for controlling trolley speed during transfer between the first and second stations and comprising a speed selector for setting a command speed value, a speed sensor assembly sensing the speed of the cable and providing a speed feedback value and a speed regulator regulating the speeds of the inhaul and the outhaul winches as a function of the command speed value and the speed feedback value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     This invention relates to an article transfer system including two winches and a cable that traverses the distance between two stations where the relative juxtaposition between the stations may change during article transfer and more specifically to a cable speed/tension control system for such a winch/cable configuration.  
         [0004]     The present invention has various applications in both the military and civilian shipping industries including transfer of articles and/or people between two ships or between a dock and a ship. Nevertheless, unless indicated otherwise, the present invention will be described in the context of a process and system for transferring supplies between a military replenishment ship and a military receiving ship requiring the supplies.  
         [0005]     Ships and other sea going vessels often spend long periods (e.g., several days, weeks or even months) out of port. To support on-board activities during these long periods at sea, typically large amounts of supplies have to be transferred to a ship for storage and subsequent use. The preferred way to transfer supplies to a ship is to have the ship dock at a port and transfer the supplies portside. Unfortunately, in the case of some ships, the potential for nefarious activities renders some ports unsafe. For instance, in the case of military ships, it is often preferred to keep military ships out of unguarded ports during replenishment activities to avoid potential illicit activities.  
         [0006]     To facilitate at sea transfer of supplies, winch/cable systems have been developed that enable ship-to-ship supply transfers. Here, the idea is that a replenishment ship loads supplies in port, leaves port to rendezvous with a receiving ship at sea (i.e., out of port) and transfers the supplies to the receiving ship at sea.  
         [0007]     To accomplish at sea transfer of supplies, a typical winch/cable transfer system includes an inhaul winch and an outhaul winch that are proximately mounted on one side of a replenishment ship and a pulley assembly mounted to a side of the receiving ship that faces the replenishment ship. A first end of a cable is received by the inhaul winch, a second end of the cable is received by the outhaul winch and the central portion of the cable extends between the replenishment ship and the receiving ship and is restricted by the pulley assembly. Thus, the cable traverses from the inhaul winch on the replenishing ship to the pulley on the receiving ship and then from the pulley to the outhaul winch on the replenishing ship. Unless indicated otherwise the cable section between the pulley and the inhaul winch will be referred to hereinafter as the inhaul cable section and the section between the pulley and the outhaul winch will be referred to as the outhaul cable section.  
         [0008]     A trolley or carriage for supporting articles for transfer is secured to the inhaul cable section for movement therewith. To move the carriage from the replenishing ship to the receiving ship, the inhaul winch rotates to let cable out while the outhaul winch takes cable in. Similarly, to move the carriage from the receiving ship back to the replenishing ship, the outhaul winch rotates to let cable out while the inhaul winch takes cable in. Hereinafter movement form the replenishing ship toward the receiving ship will be referred to as an outhaul activity or “outhauling” and movement from the receiving ship to the replenishing ship will be referred to as an inhaul activity or “inhauling” (i.e., movement will be referred to relative to the replenishing ship).  
         [0009]     A typical winch/cable control system includes a user operated control handle or throttle located at an operator&#39;s observation deck—the deck being located on the replenishing ship at a best location for observing system operations. The throttle facilitates simultaneous adjustment of both the inhaul and outhaul winches so that operation of the two winches can be essentially synchronized. The throttle has inhaul and outhaul directions and typically enables a range of load dependent inhaul and outhaul speeds. Typically, to adjust trolley speed, a system operator acts as a feedback system by visually observing trolley movement between the replenishing and receiving ships and throttling speed appropriately—e.g., speed is generally increased and decreased by altering throttle position.  
         [0010]     Trolley speed control is important for various reasons. First, often the amount of supplies that have to be transferred between ships is relatively large. Large supply transfer requirements coupled with a general requirement that transfer periods be kept to a minimum (especially in the case of military replenishment activities where ships may be relatively more vulnerable during replenishment activities) means that high speed transfer is a high priority in many applications.  
         [0011]     Second, while trolley speed should be high when a trolley is safely away from each of the replenishing ship and the receiving ship, trolley speed should be much lower and relatively precisely controlled when a trolley is located proximate either of the replenishing ship or the receiving ship to avoid potential damage to the articles being transferred, the trolley, the cable and/or to ship structure.  
         [0012]     Exacerbating transfer tasks and increasing the likelihood of damage to articles being transferred and/or system components, during ship-to-ship transfers that take place outside protected ports, unpredictable sea swells and waves cause adjacent ships to heave, bob and roll according to different cycles so that relative juxtapositions of the replenishing ship winches and the receiving ship pulley assembly change in non-determinant ways. For instance, if a replenishing ship and a receiving ship linked thereto both roll toward each other at the same time the vertical height of a trolley therebetween may drop rapidly toward the surface of the sea there below. Similarly, if the replenishing ship and the receiving ship roll away from each other at the same time vertical height may change rapidly (e.g., an upward sling-shot activity may result in this case). Slow trolley speeds proximate ships reduce the likelihood of system component damage.  
         [0013]     Rapid changes in vertical trolley height can be approximated by cable tensions and thus cable tensions can be adjusted to compensate for relative ship heaving, rolling and bobbing thereby generally maintaining control of vertical trolley height. Thus, for instance, where adjacent cable linked ships roll toward each other at the same time the cable tensions of each of the inhaul and outhaul cable sections are reduced appreciably. Here, winch control can be used to maintain a constant cable tension such that the vertical position of the trolley is essentially maintained. Similarly, where adjacent cable linked ships roll away from each other at the same time, the cable tensions of each of the inhaul and outhaul cable sections are increased appreciably. Here, again, winch control can be used to maintain a constant cable tension such that the vertical position of the trolley is essentially maintained.  
         [0014]     An exemplary tension regulating system includes inhaul and outhaul tension sensors associated with the inhaul and the outhaul winches, respectively. Each sensor generates a tension signal which is fed back to a winch controller. The controller compares the tension feedback signals to previous tension signals and adjusts winch cable intake and cable output to maintain constant cable tensions and hence to generally maintain trolley height during transfer.  
         [0015]     Unfortunately, while control systems like the ones described above work well in theory, these systems have failed to provide accurate trolley speed control. In this regard, as in most throttle based control systems, trolley speed is a function of both power into the winch and the load associated with the winch. Thus, for instance, for a given throttle position, all other factors assumed equal, a first load may have a higher speed than a second load where the second load is three times as heavy as the first load.  
         [0016]     In addition, even for a specific article to be transferred, the effective load on winches may vary so that trolley speed is different despite the same throttle position. For instance, in one case, assume that a receiving ship deck is 30 feet above the winches on the replenishing ship while in another case the receiving ship deck is 20 feet below the winches. Here, despite the same article to transfer, the loads on the winches differ appreciably and a single throttle position would result in two different speeds.  
         [0017]     Moreover, in a typical case, winch load changes during article transfer activity and the load changes affect trolley speed. Here, again assume that a receiving ship deck is approximately 30 feet above the replenishing ship winches but that large sea swells cause the relative height difference to change between 25 and 35 feet. Here, during transfer, winch loads and hence trolley speed change appreciably.  
         [0018]     Furthermore, systems that maintain cable tension, in some cases, can exacerbate the speed regulating problems described above. In this regard, some tension maintaining algorithms may cause effects that compound load varying effects of sea swells and the like. For instance, assume that a sea swell reduces a difference in height between a receiving ship deck and the replenishing ship winches so that the winch loads are generally reduced thereby increasing trolley speed. Here, as the relative vertical dimension between the winches and the receiving deck changes the tension sensors may cause the winches to maintain a constant tension which could increase trolley speed further thereby causing a compounding effect.  
         [0019]     A problem related to varying trolley speed is that, in many applications, while a system operator will be positioned so as to have the best possible view of the overall transfer system, even the best possible view does not facilitate very good observation of activities and, more specifically, of trolley speed at the receiving ship end of the configuration. In some cases the operator&#39;s observation deck may be 20 or more yards from the receiving deck and hence visual speed determination will be poor at best.  
         [0020]     Thus, there is a need for a controller that provides precise trolley speed control in a ship supply transfer configuration.  
       BRIEF SUMMARY OF THE INVENTION  
       [0021]     It has been recognized that a speed feedback loop can be added to a winch control system to configure a much better control configuration for use with a ship supply transfer system. The speed feedback loop enables configuration of a true speed controller as opposed to a throttle so that a winch/cable system operator can select a load-independent trolley speed by positioning a speed control input device and needn&#39;t be concerned that trolley speed will change as a function of other factors such as relative ship heaving, bobbing and rolling due to sea swells and the like. The end result is a much more controllable system in which operators become far more confident and transfer speed is increased appreciably.  
         [0022]     In at least some inventive embodiments two cable speed sensors, an initial sensor for measuring speed of a cable section proximate the inhaul winch and an outhaul sensor for measuring speed of a cable section proximate the outhaul winch, are provided. Which cable speed signal is used in the speed loop, the outhaul or inhaul signal, is a function of whether or not the trolley is being moved in the outhaul or inhaul directions. In at least some embodiments, when the trolley is outhauling, the inhaul speed sensor signal is used for feedback and, when the trolley is inhauling, the outhaul speed sensor signal is used for feedback.  
         [0023]     When the difference between a commanded speed and the value of the speed feedback signal is negative, the inhaul winch torque is increased while the outhaul winch torque is set to some nominal value corresponding to a minimum cable tension. For instance, if the trolley is outhauling and the speed of a section of cable proximate the inhaul winch is higher than the commanded speed, the inhaul winch torque is increased to slow the inhaul winch down thereby reducing speed. As another instance, if the trolley is inhauling and the magnitude of the speed of the section of cable proximate the outhaul winch is less than the magnitude of the commanded speed, the inhaul winch torque is increased to speed up trolley movement.  
         [0024]     Similarly, when the difference between the commanded speed and the speed feedback signal is positive, the outhaul winch torque is increased while the inhaul winch torque is set to some nominal value corresponding to a minimum tension cable.  
         [0025]     In at least some embodiments, in addition to the speed feedback loop, a tension feedback system is employed to maintain a suitable tension on the system cables thereby minimizing rapid changes in vertical trolley position. Here, in at least some embodiments, when the speed error (e.g., command speed less feedback speed value) is positive, the outhaul torque is set as a function of a minimum cable tension reference while the inhaul torque is set as a function of the minimum cable tension reference, an inhaul tension feedback signal and the speed error. In this way, when outhaul or inhaul speed is too slow, the outhaul winch torque increase is made a function of inhaul cable tension so that, if the inhaul cable tension is lower than a minimum value, the torque is increased more rapidly and, if the inhaul cable tension is higher than the minimum value the torque increase is slower. Similarly, when the speed error is negative, the inhaul torque is set as a function of the minimum cable tension reference while the outhaul torque is stepped up or down at a rate that depends on the cable tension proximate the outhaul winch.  
         [0026]     Consistent with the above, the present invention includes an apparatus for use with a transfer system for transferring a trolley between first and second stations, the system including an inhaul winch, an outhaul winch, a cable and a trolley, the inhaul winch mounted to the first station, the outhaul winch mounted to one of the first and second stations, the cable extending between the first and second stations and between the inhaul and outhaul winches and the trolley mounted to the cable, the assembly for controlling trolley speed during transfer between the first and second stations and comprising a speed selector for setting a command speed value, a speed sensor assembly sensing the speed of the cable and providing a speed feedback value and a speed regulator regulating the speeds of the inhaul and the outhaul winches as a function of the command speed value and the speed feedback value.  
         [0027]     In some embodiments the speed sensor assembly includes an inhaul speed sensor, an outhaul speed sensor and a feedback determiner, the inhaul speed sensor sensing the speed of the cable proximate the inhaul winch and generating an inhaul speed feedback signal and the outhaul speed sensor sensing the speed of the cable proximate the outhaul winch and generating an outhaul speed feedback signal, the feedback determiner selecting one or the other of the inhaul and outhaul speed feedback signals as the speed feedback value. In some embodiments, when the winches are moving the trolley from the first station toward the second station, the feedback determiner selects the inhaul speed feedback signal as the speed feedback value and, when the winches are moving the trolley from the second station toward the first station, the feedback determiner selects the outhaul speed feedback signal as the speed feedback value.  
         [0028]     Some embodiments include a pulley mounted to the second station and wherein the outhaul winch is mounted to the first station and the cable passes from the inhaul winch around the pulley and back to the outhaul winch.  
         [0029]     The speed sensor assembly may include first and second cable speed sensors for determining the speed of two different sections of the cable. Here, the speed sensor assembly may further include a speed feedback determiner for selecting a signal from one of the first and second cable speed sensors as the speed feedback value. In some cases the first and second speed sensors include an inhaul speed sensor for sensing the speed of the cable proximate the inhaul winch and an outhaul speed sensor for sensing the speed of the cable proximate the outhaul winch, respectively, and, wherein, the speed feedback determiner selects the inhaul sensor signal when the inhaul winch is letting cable out and selects the outhaul sensor signal when the outhaul winch is letting cable out.  
         [0030]     The speed regulator may include a summer that mathematically combines the command speed value and the speed feedback value to generate a speed error value and then uses the speed error value to adjust inhaul and outhaul winch speeds. Here, when the speed error value is positive, the speed regulator may use the speed error value as an intermediate outhaul speed value to control the outhaul winch and a zero intermediate inhaul speed value to control the inhaul winch and, when the speed error value is negative, the speed regulator may use the speed error value as an intermediate inhaul speed value to control the inhaul winch and a zero intermediate outhaul speed value to control the outhaul winch.  
         [0031]     The apparatus may further include a tension selector for setting a command tension value, the speed regulator mathematically combining the command tension value and the intermediate inhaul speed value to generate an inhaul torque value to control the inhaul winch speed and mathematically combining the command tension value and the intermediate outhaul speed value to generate an outhaul torque value to control the outhaul winch speed. The apparatus may further include inhaul and outhaul tension sensors for sensing cable tensions proximate the inhaul and outhaul winches and generating inhaul and outhaul tension feedback values, respectively, when the error signal is negative, the speed regulator mathematically combining to generate the outhaul torque value by mathematically combining the command tension value and the outhaul tension feedback value to generate an intermediate outhaul tension value, mathematically combining the command tension value and the intermediate outhaul tension value to generate a final outhaul tension value and mathematically combining the intermediate outhaul speed value and the final outhaul tension value to generate the outhaul torque value; and, when the error signal is positive, the speed regulator mathematically combining to generate the inhaul torque value by mathematically combining the command tension value and the inhaul feedback tension value to generate an intermediate inhaul tension value, mathematically combining the command tension value and the intermediate inhaul tension value to generate a final inhaul tension value and mathematically combining the intermediate inhaul speed value and the final inhaul tension value to generate the inhaul torque value. The summer may mathematically combine the command speed value and the speed feedback value by subtracting the speed feedback value from the command speed value.  
         [0032]     Some embodiments further include a cable tension selector for selecting a cable tension command value, the speed regulator regulating the speeds of the inhaul and the outhaul winches as a function of the command speed value, the speed feedback value and the cable tension command value. Here, the apparatus may further include an inhaul cable tension sensor and an outhaul cable tension sensor for sensing the tension of the cable proximate the inhaul and outhaul winches and generating inhaul and outhaul tension feedback values, respectively, the speed regulator regulating the speeds of the inhaul and the outhaul winches as a function of the command speed value, the speed feedback value, the cable tension command value and the inhaul and outhaul tension feedback values.  
         [0033]     The speed sensor assembly in some cases includes first and second cable speed sensors for determining the speeds of two different sections of the cable and wherein the speed sensor assembly further includes a speed feedback determiner for selecting a signal from one of the first and second cable speed sensors as the speed feedback value.  
         [0034]     The invention also includes an apparatus for use with a transfer system for transferring a trolley between first and second stations, the system including an inhaul winch, an outhaul winch, a cable, a trolley and a pulley, the inhaul winch and outhaul winch mounted to the first station, the pulley mounted to the second station, the cable extending from the inhaul winch to the pulley and back to the outhaul winch and the trolley mounted to the cable, the assembly for controlling trolley speed during transfer between the first and second stations and comprising a speed selector for setting a command speed value, the command speed value positive when the winches are operating to move the trolley toward the second station and negative when the winches are operating to move the trolley toward the first station, an inhaul speed sensor for sensing cable speed proximate the inhaul winch and generating an inhaul speed feedback value, an outhaul speed sensor for sensing cable speed proximate the outhaul winch and generating an outhaul speed feedback value, a speed feedback determiner that selects the inhaul speed feedback value as a speed feedback value when the command speed value is positive and selects the outhaul speed feedback value as the speed feedback value when the command speed value is negative and a speed regulator that regulates the torques of the inhaul and the outhaul winches as a function of the command speed value and the speed feedback value.  
         [0035]     The invention further includes a method for use with a transfer system for transferring a trolley between first and second stations, the system including an inhaul winch, an outhaul winch, a cable, a trolley and a pulley, the inhaul winch and outhaul winch mounted to the first station, the pulley mounted to the second station, the cable extending from the inhaul winch to the pulley and back to the outhaul winch and the trolley mounted to the cable, the method for controlling trolley speed during transfer between the first and second stations and comprising the steps of providing a command speed value that is positive when the trolley is being moved from the first toward the second station and that is negative when the trolley is being moved from the second to toward the first station, identifying an inhaul speed feedback value by determining the speed of a section of the cable proximate the inhaul winch, identifying an outhaul speed feedback value by determining the speed of a section of the cable proximate the outhaul winch, when the command speed value is positive, selecting the inhaul speed feedback value as a speed feedback value, when the command speed value is negative, selecting the outhaul speed feedback value as a speed feedback value and regulating winch torques as a function of the command speed value and the speed feedback value.  
         [0036]     Furthermore, the invention includes a transfer assembly for transferring between first and second stations, the assembly comprising an inhaul winch mounted to the first station, an outhaul winch mounted to one of the first and second stations, a cable extending between the first and second stations and between the inhaul and outhaul winches, a trolley mounted to the cable, a speed selector for setting a command speed value, a speed sensor assembly sensing the speed of the cable and providing a speed feedback value and a speed regulator regulating the speeds of the inhaul and the outhaul winches as a function of the command speed value and the speed feedback value.  
         [0037]     These and other objects, advantages and aspects of the invention will become apparent from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention and reference is made therefore, to the claims herein for interpreting the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0038]      FIG. 1  is a schematic diagram illustrating a transfer assembly according to the present invention wherein a replenishment ship deck is vertically higher than a receiving ship deck;  
         [0039]      FIG. 2  is a is similar to  FIG. 1 , albeit illustrating a system wherein the replenishment ship deck is vertically below the receiving ship deck;  
         [0040]      FIG. 3  is a schematic diagram illustrating four quadrants of trolley control where the quadrants are a function of outhaul to inhaul cable differential and trolley speed;  
         [0041]      FIG. 4  is a schematic diagram of a control system according to one embodiment of the present;  
         [0042]      FIG. 5  is a schematic diagram of a section of a control system that may be used to replace a section of the control system of  FIG. 4  and that includes a closed tension loop;  
         [0043]      FIG. 6  is a flow chart illustrating one method according to the present invention; and  
         [0044]      FIG. 7  is similar to  FIG. 6  albeit illustrating a second method according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]     Hereinafter, unless indicted otherwise, an “*” will be used to identify reference or command signals, a subscript “e” will used to indicate an error signal, a “fb” will be used to indicate a feedback signal, a subscript “o” will be used to indicate a signal associated with either an outhaul winch or a section of cable proximate an outhaul winch, a subscript “i” will be used indicate a value associated with an inhaul winch or a section of cable proximate an inhaul winch, a subscript “int” will be used to indicate an intermediate value and subscript “f” will be used to indicate a final value. In some cases subscripts identified above will be combined to indicate several characteristics of a signal associated therewith. For example, the symbol S fbo  will be used hereinafter to indicate a feedback speed signal corresponding to a section of cable proximate an outhaul winch. Similarly, the symbol S inti  will be used to refer to an intermediate speed signal associated with an inhaul winch. Also, to simplify this explanation, the phrases “inhaul cable tension” and “outhaul cable tension” will be used to refer to the sections of a cable proximate an inhaul winch and an outhaul winch, respectively.  
         [0046]     A. Overview of Transfer Components  
         [0047]     Referring now to the drawings and, more specifically, referring to  FIG. 1 , the present invention will be described in a context of an exemplary ship to ship replenishment system  10 . In  FIG. 1 , a replenishment ship  12  is employed to transfer a trolley  28  and items thereon to a receiving ship  14 . To accomplish this task, ship  12  includes an elevated operator observation and control station  16 , an inhaul winch assembly  18  and an outhaul winch assembly  22 . The inhaul and outhaul winch assemblies  18  and  22 , respectively, are mounted to the replenishment ship deck in a rigid fashion and adjacent one side of the ship.  
         [0048]     A receiving ship  14  includes a pulley assembly  20  mounted on the top of one of its decks and adjacent one side of the ship  14 . Pulley assembly  20  cooperates with winch assemblies  18  and  22  in a manner to be described in more detail below.  
         [0049]     In addition to the components described above, the replenishment assembly  10  also includes a high tension cable generally identified by numeral  27  which has first and second ends (not separately numbered). In a typical set up, a first end of cable  27  is received by inhaul winch assembly  18  and is wrapped around that winch assembly multiple times. Cable  27  extends from inhaul winch  18  to receiving ship  14 , wraps around pulley assembly  20  and then traverses the distance back to replenishment ship  12  where the second end of cable  27  is received and wrapped around inhaul winch  22 . Trolley  28  is mounted to the portion of cable  27  that extends from inhaul winch assembly  18  to pulley assembly  20 .  
         [0050]     It should be appreciated that, by simultaneously controlling inhaul and outhaul winch assemblies  18  and  22 , respectively, trolley  28  attached to cable  27  can be moved in either direction between replenishment ship  12  and receiving ship  14 . Hereinafter, unless indicated otherwise, when winch assemblies  18  and  22  are used to move trolley  28  from replenishment ship  12  toward receiving ship  14 , the operation will be referred to as an outhaul or outhauling operation. Similarly, when winch assemblies  18  and  22  are used to move trolley  28  in the direction from receiving ship  14  to replenishment ship  12 , the operation will be referred to as an inhaul or inhauling operation. Outhauling and inhauling movement are identified by arrows  32  and  30 , respectively, in  FIG. 1 . In addition, the section of cable  27  proximate inhaul winch assembly  18  at any given time (i.e., the proximate section changes as the winch is rotated) will be referred to as the inhaul cable section  24  and the section of cable  27  proximate the outhaul winch assembly will be referred to as the outhaul cable section  26 .  
         [0051]     Each of the inhaul and outhaul winch assemblies  18  and  22 , respectively, includes a motor, a clutch and a drum. Referring also to  FIG. 4 , the inhaul winch clutch and drum are identified by numerals  98  and  96 , respectively, which the outhaul winch clutch and drum are identified by numerals  92  and  94 , respectively. A single motor  102  is illustrated that is coupled to each of drums  94  and  96  via their associated clutches  92  and  98 . Motor  102  is typically set to operate and rotate a motor rotor at a single speed. To increase torque on the drums  94  and  96  and hence winch speed, the slip between the clutches  92  and  98  and the motor rotor is decreased. Similarly, to decrease drum speed the slip between a clutch and the motor rotor is increased.  
         [0052]     Referring again to  FIG. 1 , controls for controlling winch assemblies  18  and  22  are provided within station  16 . Referring also to  FIG. 4 , among other controls, the controls provided in station  16  include a speed selector  52  and a minimum cable tension selector  80 . In at least one embodiment, speed selector  52  includes a potentiometer which outputs a voltage within an appropriate range. For instance, an exemplary speed selector output may be anywhere within a range of −10 volts to +10 volts where a positive value indicates outhaul control (i.e., movement of trolley  28  from replenishment ship  12  to receiving ship  14 ) and a negative value indicates inhaul control. The minimum cable tension selector  80 , in some embodiments, will also include a potentiometer. The output of minimum cable tension selector  80  will always be positive and, for instance, may have a range between zero and +10 volts.  
         [0053]     B. Control Algorithm  
         [0054]     Referring yet again to  FIG. 1 , in some cases the relative heights of the replenishment ship deck and the receiving ship deck will be such that the winch assemblies  18  and  22  reside at a higher elevation than the receiving pulley assembly  20 . In this case, it should be appreciated that, because trolley  28  moves downward when traversing in the outhaul direction  32 , trolley  28 , acting under the force of gravity, in effect, pulls cable from inhaul winch assembly  18 . This pulling force on assembly  18  is such that the trolley load attempts to rotate the winch drum more quickly than commanded by the system operator. Thus, when winch assemblies  18  and  22  are vertically relatively higher than pulley assembly  20  and trolley  28  is moved in outhaul direction  32 , inhaul winch assembly  18  operates as a braking system to hold back trolley  28  and control trolley speed. Hereinafter, unless indicated otherwise, where trolley  28  movement results in a pulling force on one of the winch assemblies  18  or  22  in the direction of trolley movement, the condition will be referred to as an “overhauling” condition.  
         [0055]     Referring now to  FIG. 2 , an exemplary system  34  similar to the system  10  illustrated in  FIG. 1  is shown. The primary difference between the systems in  FIGS. 1 and 2  is that the receiving ship  37  deck in  FIG. 2  is much higher than the deck of receiving ship  14  in  FIG. 1  such that pulley assembly  38  on receiving ship  37  is vertically relatively higher than assemblies  18  and  22  mounted to replenishment ship  12 . In  FIG. 2 , the inhaul and outhaul directions are identified by arrows  35  and  36 , respectively. Importantly, when the receiving ship pulley assembly  38  is higher than the winch assemblies  18  and  22  on the replenishment ship  12 , overhauling conditions occur when trolley  28  is moving in inhauling direction  35  as opposed to outhauling direction  36 . Here, the overhaul pulling force of trolley  28  is on the outhaul winch assembly  22  as opposed to the inhaul assembly  18 . Hence, when moving in direction  35 , trolley  28  tends to pull the cable from outhaul winch assembly  22  and winch assembly  22  operates as a brake on trolley speed.  
         [0056]     Referring again to  FIG. 1 , when winch assemblies  18  and  22  are vertically relatively higher than pulley assembly  20  and trolley  28  is moving in inhauling direction  30 , a normal load condition occurs where the force exerted by trolley  28  is against the rotating directions of each of trolley assemblies  18  and  22 . Similarly, in  FIG. 2 , a normal load condition occurs when trolley  28  is moved in outhauling direction  36 .  
         [0057]     In addition to the conditions described above, there are two other interesting operating conditions including accelerating and decelerating conditions. With respect to trolley deceleration, deceleration generally requires one or other of the winch assemblies  18  or  22  to operate as a braking mechanism to slow trolley movement independent of whether or not the trolley is moving in the inhaul direction or outhaul direction. For example, referring again to  FIG. 1 , assuming trolley  28  is moving in inhaul direction  30  and hence a normal load condition occurs. In this case, to decelerate trolley  28 , outhaul winch  22 , at least instantaneously, operates as a braking mechanism to slow trolley movement. Similarly, referring to  FIG. 2 , assuming trolley  28  is moving in outhaul direction  36  and hence a normal load occurs, to decelerate trolley  28 , inhaul winch assembly  18  instantaneously operates as a braking mechanism.  
         [0058]     With respect to acceleration, regardless of whether or not trolley  28  is moving in the inhaul direction or outhaul direction, an accelerating trolley  28  results in forces on assemblies  18  and  22  that are akin to normal load forces. For instances, referring again to  FIG. 1 , assuming trolley  28  is moving in outhaul direction  32  and winch assemblies  18  and  22  are currently being controlled to accelerate trolley  28 , instantaneously, the winch speeds are increased and, in particular, the speed of inhaul winch assembly  18  exceeds the speed at which trolley  28  pulls cable from assembly  18 . Similarly, referring again to  FIG. 2 , when trolley  28  is moving in inhaul direction  35  and assemblies  18  and  22  are controlled to accelerate trolley  28  in inhaul direction  35 , instantaneously, the rotating speed of assembly  22  increases beyond the speed at which the trolley load  28  would draw cable from assembly  22 .  
         [0059]     Referring now to  FIG. 3 , a graph showing four exemplary quadrants of system operation is illustrated. In  FIG. 3 , four quadrants are defined by vertical and horizontal axes  40  and  42 , respectively. The vertical axis  40  corresponds to cable tension differential. The top half of axis  40  corresponds to a condition wherein the outhaul cable section  26  tension is greater than the inhaul cable section  24  tension. Similarly, the bottom half of vertical axis  40  corresponds to conditions wherein the inhaul cable section  24  tension is greater than the outhaul cable section  26  tension. The left half of horizontal axis  42  corresponds to inhauling conditions where trolley  28  is being moved from the receiving ship to the replenishment ship (e.g., from ship  14  to ship  12  in  FIG. 1 ). The right half of horizontal axis  42  corresponds to conditions wherein trolley  28  is moving from the replenishment ship to toward the receiving ship.  
         [0060]     Referring still to  FIG. 3 , the outhaul cable section  26  tension will be greater than the inhaul cable section  24  tension under several different sets of circumstances. First, referring again to  FIG. 2 , during a normal load condition with trolley  28  moving in outhauling direction  36 , outhaul cable section  26  tension is greater than the inhaul cable section  24  tension proximate inhaul winch  18 . Second, whenever outhauling and accelerating trolley  28 , irrespective of whether or not the load is an overhauling load (see again  FIG. 1 ) or a normal load (see again  FIG. 2 ), the outhaul cable section  26  tension is greater than the inhaul cable section  24  tension. Both of these two sets of circumstances correspond to quadrant  1  in  FIG. 3 .  
         [0061]     Referring still to  FIG. 3 , a third set of circumstances under which the outhaul cable section  26  tension will be greater than the inhaul cable section  24  tension occurs whenever trolley  28  is inhauled and operates as an overhauling load. To this end, referring again to  FIG. 2 , when trolley  28  is inhauled in direction  35  and pulley assembly  38  is vertically higher than winch assemblies  18  and  22  such that an overhauling condition occurs, tension of cable section  26  proximate outhaul winch assembly  22  is greater than the tension in cable section  24  proximate inhaul winch assembly  18 . Fourth, the outhaul cable section  26  tension is greater than the inhaul cable tension whenever inhauling trolley  28  when winch assemblies  18  and  22  are operated to decelerate trolley  28  irrespective of whether or not trolley  28  corresponds to a normal or overhauling load. These third and fourth sets of conditions under which the outhaul cable section  26  tension is greater than the inhaul cable section  24  tension correspond to quadrant  2  in  FIG. 3 .  
         [0062]     Referring once again to  FIG. 3 , the inhaul cable section  24  tension will be greater than the outhaul cable section  26  tension under several sets of circumstances. First, referring again to  FIG. 1 , whenever trolley  28  is moved in the inhaul direction  30  and operates as a normal load, the tension of cable section  24  adjacent inhaul winch assembly  18  is greater than the tension of section  26  adjacent outhaul winch assembly  22 . Second, whenever inhauling trolley  28  and winch assemblies  18  and  22  are controlled to accelerate the trolley  28 , irrespective of whether or not trolley  28  is operating as a normal or an overhauling load, the inhaul cable section  24  tension is greater than the outhaul cable section  26  tension. Each of the first two conditions described above wherein the inhaul cable section tension is greater than the outhaul cable section tension correspond to quadrant  3  in  FIG. 3 .  
         [0063]     Referring yet again to  FIG. 3 , a third set of circumstances in which the inhaul cable section  24  tension is greater than the outhaul cable section  24  tension occurs whenever trolley  28  is moved in an outhaul direction and operates as an overhauling load. In this regard, referring again to  FIG. 1 , when trolley  28  is moved in outhaul direction  32  and is moving downward from inhaul winch assembly  18  to pulley  20 , the tension of cable section  24  proximate inhaul winch assembly  18  is greater than the tension of cable section  26  proximate outhaul winch assembly  22 . Fourth, when trolley  28  is moving in an outhaul direction and winch assemblies  18  and  22  are controlled to decelerate trolley  28 , irrespective of whether or not trolley  28  is operating as an overhauling load or a normal load on winch assemblies  18  and  22 , the inhaul cable section  26  tension is greater than the outhaul cable section  26  tension. The third and fourth sets of circumstances under which the inhaul cable section tension is greater than the outhaul cable section tension described above correspond to quadrant  4  in  FIG. 3 .  
         [0064]     Referring still to  FIGS. 1 and 2 , and also again to  FIG. 4 , according to one aspect of the present invention, two separate cable speed sensors  100  and  104  are provided wherein the first speed sensor  104  senses the speed of cable section  24  proximate the inhaul winch  18  and the second sensor  100  senses the speed of the cable section  26  proximate outhaul assembly  22 . These cable speed signals are fed back to a winch assembly controller and used thereby to adjust winch operation so that trolley speed is maintained at the speed selected by a system operator via speed selector  52 .  
         [0065]     According to one aspect of the present invention, which speed feedback signal, the inhaul or the outhaul speed feedback signal, is used to adjust winch operation, is a function of the operating characteristics of the winch assembly as a whole. More specifically, which feedback signal is used by the controller to adjust winch operation depends upon in which of the four quadrants illustrated in  FIG. 3  the system is operating. In this regard, when the system is operating in either of the acceleration/normal load quadrants, quadrants  1  and  3 , it has been recognized that either of the inhaul cable speed or the outhaul cable speed can, theoretically, be utilized as an accurate trolley speed feedback signal. Referring once again to  FIG. 1 , when moving trolley  28  in inhaul direction  30  and not decelerating, the speeds of cable sections  24  and  26  will be essentially identical and hence which speed feedback is used to adjust winch control is irrelevant. Similarly, referring to  FIG. 2 , when trolley  28  is moved in outhaul direction  36  and is not being decelerated, the speeds of cable sections  24  and  26  will be essentially identical and which speed feedback is used for control purposes will be irrelevant.  
         [0066]     Referring again to  FIG. 3 , when system operation is in either of the deceleration/overhauling load quadrants, quadrants  2  or  4 , the speed of the cable section being wound or taken up cannot be used as a speed feedback signal because the speed of the take up cable section is not a reliable reflection of trolley speed. For example, referring again to  FIG. 1 , when trolley  28  is moving in outhaul direction  32  and is operating as an overhauling load, winch assembly  18  operates as the braking mechanism against the overhauling load thereby maintaining trolley speed while outhaul winch assembly  22  simply takes up slack. Referring again to  FIG. 2 , similarly, when moving trolley  28  in inhaul direction  35  while trolley  28  operates as an overhauling load, outhaul winch assembly  22  operates as a brake on trolley  28  speed while inhaul winch  18  simply operates to take up cable slack.  
         [0067]     Thus, when a system operates in either quadrants  2  or  4  in  FIG. 3 , it is necessary to use the speed of the cable corresponding to the winch assembly letting out cable as the feedback for speed regulation. Referring again to  FIG. 3 , this means that during quadrant  4  operation the speed of cable section  24  proximate inhaul winch assembly  18  must be used as the speed feedback and, when operating in quadrant  2 , the speed of cable section  26  proximate outhaul winch assembly  22  must be used as the speed feedback signal for speed regulation.  
         [0068]     Referring yet again to  FIG. 3 , it should be appreciated that which speed feedback signal can be used to regulate winch assembly speeds is dependent upon two factors. First, which feedback signal can be used depends upon whether or not the trolley is inhauling or outhauling. Second, which feedback signal can be used depends on whether or not trolley  28  is operating as an overhauling load or is being decelerated on one hand or, is operating as a normal load or is being accelerated on the other hand.  
         [0069]     Whether or not the trolley is moving in the inhaul direction or the outhaul direction is easy to determine. In this regard, the speed command signal S* generated by selector  52  (see again  FIG. 4 ) can be used determine whether or not the trolley is outhauling or inhauling. Where speed command signal S* is positive, the trolley is being moved in the outhaul direction and, where speed command signal S* is negative, the trolley is being moved in the inhaul direction.  
         [0070]     Unfortunately, it is more difficult to accurately determine whether or not the trolley is operating as an overhauling load or as a normal load and, whether or not the trolley is being accelerated or decelerated. To this end, referring again to  FIG. 2 , it should be appreciated that during an initial stage of transferring a trolley  28  from replenishment ship  12  to receiving ship  37 , despite the fact that pulley assembly  38  may be vertically higher than inhaul winch assembly  18 , the trolley  28  may initially operate as an overhauling load on winch assembly  18  if there is slack in the cable  27 . After traveling in direction  36  for some time, trolley  28  may in fact operate as a normal load on winch assembly  18 , once trolley  28  is vertically higher than assembly  18 .  
         [0071]     Applicants have recognized that, while it is possible for system control to jump from any of the four quadrants illustrated in  FIG. 3  into any of the other four quadrants illustrated, under normal operating conditions, most transitions will be between quadrants  1  and  4  or between quadrants  2  and  3 . Thus, when moving trolley  28  in an outhauling direction, typically, the outhauling direction will not change and instead, trolley speed may be altered, the loading effect of the trolley (e.g., normal or overhauling) may change, etc. Similarly, when operating in the inhaul direction, while various operating parameters and the loading effect of the trolley may change, the inhauling direction will typically remain the same.  
         [0072]     Realizing that the outhauling and inhauling directions generally remain the same during system operation and that there is no easy way to determine whether or not the trolley is operating as a normal load or an overhauling load, a simplified control algorithm has been selected according to at least some embodiments of the present invention wherein, which speed feedback is selected, depends only upon the polarity of speed command signal S* (i.e., depends only upon whether or not the trolley is moving in the outhauling or inhauling direction). Referring again to  FIG. 3 , because transitions between quadrants  1  and  4  are common and either the inhaul or outhaul cable speed may be used as a feedback signal in quadrant  1  while only the inhaul cable speed can be used as a feedback signal in quadrant  4 , in at least some embodiments of the invention, whenever trolley  28  is being moved in the outhauling direction, the feedback signal used for speed regulation is the inhaul speed feedback signal. Similarly, because transitions between quadrants  2  and  3  are common and either the inhaul or the outhaul speed feedback signal can be used for speed regulation in quadrant  3  while only the outhaul speed feedback signal can be used for speed regulation in quadrant  2 , in at least some embodiments, whenever trolley  28  is being moved in the inhaul direction, the outhaul speed feedback signal is selected for speed regulation purposes. Table 1 below summarizes operating characteristics and which sensors to use in at least some embodiments for speed feedback.  
                               TABLE 1                                   Speed                       Sensors   Sensor                   Useable To   Used To                   Accurately   Accurately       Quad-   Cable   Measure   Measure       rant   Trolley Speed   Tension   Speed   Speed                   1   Outhauling Acceleration   Outhaul &gt;   Inhaul or   Inhaul           and Normal Load   Inhaul   Outhaul   Speed           (Sfb &lt; S*)       Speed   Sensor                   Sensor       2   Inhauling Deceleration   Inhaul &gt;   Outhaul   Outhaul           and Overhauling Load   Outhaul   Speed   Speed           (Sfb &lt; S*)       Sensor   Sensor       3   Inhauling Acceleration   Inhaul &gt;   Inhaul or   Outhaul           and Normal Load   Outhaul   Outhaul   Speed           (Sfb &lt; S*)       Speed   Sensor                   Sensor       4   Outhauling Deceleration   Outhaul &gt;   Inhaul   Inhaul           and Overhauling Load   Inhaul   Speed   Speed           (Sfb &gt; S*)       Sensor   Sensor                  
 
         [0073]     C. Exemplary Control System  
         [0074]     Referring to  FIG. 4 , an exemplary control system  50  according to the present invention is illustrated. System  50  includes speed selector  52 , minimum tension selector  80 , two analog-to-digital (A/D) converters  54  and  81 , two frequency-to-digital (F/D) converters  62  and  66 , a dead band regulator  56 , a speed feedback determiner  64 , three summers  58 ,  76  and  78 , one proportional-integral (PI) regulator  60 , an inverter  70 , two maximum value selectors  68  and  72 , two multipliers  74  and  82 , two digital-to-analog converters  84  and  86 , two electrical-pneumatic (E/P) controllers  88  and  90 , an inhaul speed sensor  104  and an outhaul speed sensor  100 . In addition to the elements described above, motor  102  is coupled to inhaul and outhaul drums  96  and  94 , respectively, by inhaul and outhaul clutch assemblies  98  and  92 , respectively. The E/P controllers  88  and  90  control clutches  92  and  98 , respectively, thereby altering the torques on and speeds of drums  94  and  96 , respectively.  
         [0075]     Speed selector  52  is used to select command speed S* which is a voltage within a specific range (e.g., between positive and negative 10 volts). Command speed signal S* is provided to A/D converter  54  which converts the analog voltage signal into a digital signal. The digital signal is provided to dead band regulator  56 . As its label implies, regulator  56  provides a dead band between trolley inhaul and trolley outhaul command signals wherein, when the command signal S* is within a small range of values around a zero value, the dead band regulator causes a zero command value to be generated. This dead band in speed regulation results in a system wherein transitions between one of the first and fourth quadrants of operation and one of the second and third quadrants operation as illustrated in  FIG. 3  will not occur. The command signal S* output by dead band regulator  56  is provided to each of summer  58  and speed feedback determiner  64 .  
         [0076]     Outhaul and inhaul speed feedback signals S fbo  and S fbi  are fed back from sensors  100  and  104  to F/D converters  62  and  66 , respectively. Converts  62  and  66  convert the feedback signals to digital signals which are provided to speed feedback determiner  64 . Speed feedback determiner  64  selects one of the speed feedback signals S fbo  or S fbi  as a speed feedback signal S fb  to be used for speed regulation purposes. Where speed command signal S* is positive, determiner  64  selects the inhaul speed feedback signal S fbi  and passes that signal as the feedback signal S fb  to summer  58 . Where speed command signal S* is negative, determiner  64  passes the outhaul feedback signal S fbo  as the speed feedback signals S fb  to summer  58 .  
         [0077]     Summer  58  subtracts the speed feedback signal S fb  from the speed command signal S* and generates a speed error signal S e  which is provided to PI regulator  60 . Regulator  60  steps up speed error signal S e  and provides the stepped up signal to each of inverter  70  and maximum value selector  68 . As its label implies, inverter  70  negates the stepped up speed error signal received from PI regulator  60  and provides the negated signal to maximum value selector  72 .  
         [0078]     Each of the maximum value selectors  68  and  72 , as their labels imply, selects the maximum one of two values that are input into the selector. In addition to the inputs from PI regulator  60  and inverter  70 , selectors  68  and  72  are each provided with a zero value as their second inputs. Thus, when the output of PI regulator  60  is positive, maximum value selector  68  passes the output of PI regulator  60  to summer  76  (i.e., selector  68  passes the greater of the output of PI regulator  60  and the zero value to summer  76 ). In addition, when the output of PI regulator  60  is positive, because inverter  70  negates the output of regulator  60 , maximum value selector  72  provides a zero value to summer  78 . When the output of PI regulator  60  is negative, maximum value selector  68  outputs a zero value to summer  76  and selector  72  provides the absolute value of the output of PI regulator  60  to summer  78 . In this manner, one of selectors  68  or  72  provides a zero value while the other of selectors  68  and  72  provides the absolute value of the output of PI regulator  60 . Hereinafter, the outputs of selectors  68  and  72  will be referred to as intermediate outhaul and intermediate inhaul speed signals or values S into  and S inti , respectively.  
         [0079]     Referring still to  FIG. 4 , tension selector  80  is used to set a minimum tension command value T* which, as described above, takes the form of a positive voltage value within a system range (e.g., the range may be between 0 and 10 volts). Command tension signal T* is provided to A/D converter  81  which converts that value into a digital signal which is provided to multipliers  74  and  82 . Outhaul and inhaul tension scaling factors Sf o  and Sf i  are selected by a system operator and are provided to multipliers  74  and  82 , respectively. Multiplier  74  multiplies the outhaul scaling factor Sf o  by the command minimum tension value T* and provides its output to summer  76 . Similarly, multiplier  82  multiplies the inhaul scaling factor Sf i  by the command tension value T* and provides its output to summer  78 .  
         [0080]     Summer  76  adds the intermediate outhaul speed signal S into  and the scaled tension value Sf o T* to generate an outhaul torque value Tor 0  which is provided to D/A converter  84 . Similarly, summer  78  adds the intermediate inhaul speed signal S inti  and the scaled inhaul tension command signal Sf i T* to generate an inhaul torque value Tor i  which is provided to D/A converter  86 .  
         [0081]     Converters  84  and  86  convert their received signals to analog signals which are provided to E/P controllers  88  and  90 , respectively. Controllers  88  and  90  control clutches  92  and  98 , respectively, and thereby control speeds of winch drums  94  and  96 , respectively.  
         [0082]     Thus, referring still to  FIGS. 1 and 4 , assume winch assemblies  18  and  22  are being operated to move trolley  28  in outhaul direction  32  toward ship  14  (i.e., command speed S* is positive). Also assume that trolley  28  is moving at a speed greater than the commanded speed S*. In this case, because the commanded speed S* is positive, regulator  64  selects the inhaul speed feedback signal. Inhaul speed feedback signal S fib  is subtracted from speed value S* yielding a negative value (i.e., S fbi &gt;S*). The negative output of PI regulator  60  causes selectors  68  and  72  to output a zero value and a positive value, respectively. The zero value is added to the scaled tension value SF o T* and has no effect on outhaul torque signal Tor o . However, the positive value from selector  72  steps up the ultimate inhaul torque value Tor i  thereby causing the inhaul winch to reduce its speed and in turn to reduce trolley speed.  
         [0083]     Referring still to  FIGS. 1 and 4 , during outhauling, if inhaul speed feedback signal S fbi  is less than commanded speed S*, an exact opposite torque adjustment occurs wherein the outhaul torque value Tor o  is stepped up and the initial torque value is set solely as a function of the scaled minimum torque value SF i T*. Similarly, if feedback value S fbo  has a magnitude that is less than the magnitude of command speed S*, speed error value S e  output by summer  58  is negative causing selector  78  to increase inhaul torque value Tor i  while outhaul torque value Tor o  is tied to scaled tension value SF o T*.  
         [0084]     Referring now to  FIG. 6 , an inventive method  150  that is performed by the control assembly illustrated in  FIG. 4  is shown. Beginning at block  152 , speed command signal S* and tension command signal T* are received. At block  154 , both the outhaul and inhaul cable speeds are sensed and outhaul and inhaul speed feedback signals S fbo  and S fbi  are provided. At block  156 , the controller determines if the system is inhauling or outhauling by comparing command speed S* to a zero value. Where command speed S* is greater than zero and hence trolley  28  is moving in the outhaul direction, control passes to block  158  where the controller selects inhaul feedback speed signal S fbi  as the speed feedback signal S fb . In the alternative, where command speed S* is less than zero and hence trolley  28  is moving in the inhaul direction, control passes to block  160  where the speed feedback signal S fb  is set equal to the outhaul feedback signal S fbo . After either block  160  or  158 , control passes to block  161 .  
         [0085]     At block  161  a speed error signal is determined by subtracting the speed feedback signal S fb  from command signal S*. At block  162  speed error signal S e  is compared to zero. Where speed error signal S e  is positive, control passes to block  168  where the intermediate outhaul speed signal S into  is set equal to the error signal S e  and the intermediate inhaul speed signal S inti  is set equal to zero. If speed error signal S e  at block  162  is negative, control passes to block  166  where the intermediate inhaul speed signal is set equal to the absolute value of the speed error signal S e  and the intermediate outhaul signal S into  is set equal to zero. After either of blocks  166  or  168 , control passes to block  170 .  
         [0086]     At block  170 , the intermediate outhaul speed signal is added to the minimum tension signal for the outhaul winch and the intermediate inhaul speed signal is added to the minimum tension of the inhaul winch thereby generating outhaul and inhaul torque signals Tor o  and Tor i , respectively. At block  172 , the outhaul and inhaul torque signals are used to control the winches. After block  172 , control again passes back up to block  162  where the process is repeated.  
         [0087]     D. Closed Loop Control System  
         [0088]     While an open tension loop embodiment of the present invention is described above, the present invention also contemplates a system having a closed tension loop. To this end, referring to  FIG. 5 , various components that may be used to supplement and replace several of the components of  FIG. 4  are illustrated. In  FIG. 5 , components that are similar or identical to the components illustrated in  FIG. 4  are identified by the same numbers. Components unique to the embodiment of  FIG. 5  include inhaul and outhaul cable tension sensors  132  and  134 , first and second tension determiners  112  and  122 , additional summers  114  and  124  and two additional PI regulators  116  and  126 .  
         [0089]     Maximum value selectors  68  and  72  in  FIG. 5  operate in the manner described above with respect to  FIG. 4  to generate intermediate outhaul and inhaul speed signals S into  and S inti , respectively, and therefore will not be described here in detail. Similarly, components  80 ,  81 ,  74  and  82  operate in the manner described above and hence will not be described again in detail.  
         [0090]     Tension sensor  132  is mounted proximate inhaul winch assembly  18  for measuring the tension of inhaul cable section  24  and generates an inhaul tension feedback signal T fbi . Similarly, sensor  134  is mounted proximate outhaul winch assembly  22  for measuring the tension of outhaul cable section  26  and generates an outhaul tension feedback signal T fbo .  
         [0091]     In addition to being provided to multipliers  74  and  82 , the digital tension command signal T* is also provided to first and second tension determiners  112  and  122 . Referring to  FIGS. 4 and 5 , first tension determiner  112  also receives the stepped up speed error signal from PI regulator  60  as well as the outhaul tension feedback signal T fbo  from outhaul cable tension sensor  134 . Second tension determiner  122  receives the output of inverter  70  and the tension feedback signal T fbi  from tension sensor  132 .  
         [0092]     Referring still to  FIG. 5 , when the output of PI regulator  60  is negative, first tension determiner  112  outputs tension command signal T* as a reference signal to summer  114  while second tension determiner  122  outputs inhaul tension feedback signal T fbi  as a reference signal to summer  124 . In the alternative, when the output of PI regulator  60  is positive, first tension determiner  112  provides outhaul tension feedback signal T fbo  from sensor  134  as a reference signal to summer  114  while second tension determiner  122  provides command tension signal T* as a reference signal to summer  124 .  
         [0093]     In addition to receiving the output from first tension determiner  112 , summer  114  also receives outhaul tension feedback signal T fbo  and subtracts feedback signal T fbo  from the reference signal thereby generating an intermediate outhaul tension signal T into . Similarly, summer  124  receives inhaul tension feedback signal T fbi  from sensor  132  and subtracts signal T fbi  from the reference signal received from determiner  122  thereby generating an intermediate inhaul tension signal T inti . Intermediate signals T into  and T inti  are provided to PI regulators  116  and  126 , respectively, which step up those signals and provide the stepped up signals to summers  120  and  130 , respectively. Summer  120  adds the received stepped up signal to scaled tension command signal Sf o T* thereby generating a final outhaul tension signal T fo . Similarly, summer  130  adds the received stepped up signal to scaled tension command signal Sf i T* thereby generating a final inhaul tension signal T fi .  
         [0094]     The final outhaul and inhaul tension signals T fo  and T fi  are provided to summers  76  and  78 , respectively. Summers  76  and  78  add the final tension values to the intermediate outhaul and inhaul speed signals S into  and S inti  thereby generating outhaul and inhaul torque signals Tor o  and Tor i , respectively. Final signals Tor o  and Tor i  are provided to D/A converters  84  and  86  as illustrated in  FIG. 4 .  
         [0095]     Thus, when speed error S e  is negative, the difference between the minimum tension command value T* and the outhaul feedback tension signal T fbo  is used to adjust the rate at which the outhaul torque is increased. For instance, if the outhaul feedback torque T fbo  is less than the minimum torque command T*, the rate of outhaul torque change is increased and if the outhaul feedback torque T fbo  is greater than the minimum torque command T*, the rate of outhaul torque change is decreased.  
         [0096]     Similarly, when speed error S e  is positive, the differential between the command value T* and the inhaul feedback tension signal T fbi  difference is used to adjust the rate at which the inhaul torque is increased (e.g., a positive T*−T fbi  differential causes the rate of torque increase to be increased and a negative differential causes a decrease in the rate).  
         [0097]     Referring now to  FIGS. 4, 5  and  7 , a process  150  that may be performed by a controller assembly including the components of  FIG. 5  is illustrated in  FIG. 7 . In  FIG. 7 , many of the steps described above with respect to  FIG. 6  are identical, are identified by identical numbers and will not be explained again here in detail in the interest of simplifying this explanation. The blocks in  FIG. 7  that are similar but not identical to the blocks in  FIG. 6  are identified by the same numbers followed a “′”. In  FIG. 7 , after block  152 , control passes to block  154 ′ where, in addition to receiving the inhaul and outhaul cable speeds, the controller also receives the inhaul and outhaul cable tension signals T fbi  and T fbo , respectively. After block  154 ′, the functions corresponding to blocks  156 ,  158 ,  160 , 161  and  162  are identical to the process blocks described above with respect to  FIG. 6 .  
         [0098]     At block  162 , where the speed error S e  is negative, control passes to block  168 ′ where, in addition to identifying the intermediate speed signals, the controller also identifies the final outhaul and final inhaul tension signals T fo  and T fi , as illustrated. Where the speed error signal S e  is positive, control passes to block  166 ′ where the intermediate speed signals are identified and the final outhaul and inhaul tension signals are identified by solving the equations illustrated. After either of block  166 ′ or block  168 ′, control passes to block  170 ′ where the intermediate speed signals and final tension signals are added together according to the illustrated equations thereby generating final outhaul and inhaul torque signals Tor o  and Tor i , respectively. At block  172 , the final torque signals are used to control the clutches and thereafter control passes back up to block  152  where the process is repeated.  
         [0099]     It should be understood that the methods and apparatuses described above are only exemplary and do not limit the scope of the invention, and that various modifications could be made by those skilled in the art that would fall under the scope of the invention.  
         [0100]     To apprise the public of the scope of this invention, the following claims are made: