US3388070A - Method and apparatus for highline tension control - Google Patents

Description

June 1968 E. H. BORN ETAL METHOD AND APPARATUS FOR HIGHLINE TENSION CONTROL Sheets-Sheet 1 June 11, 1968 E. H. BORN ET AL. 3,388,070

METHOD AND APPARATUS FOR HIGHLINE TENSION CONTROL Filed Feb. 25, 1967 SHIP SEPARATION 2 Sheets-Sheet 2 I A L. BS98 3 Q L E'LQ L SHIP CLOSURE ATED WINCH OPER TO PAY OU CABLE SHIP SEPARATION SHIP CLOSURE HYPOTHETICALRAM TENSION"\\\ osmou IF NO CORRECTION I [OR RA TE OF POSITION CHANQE Rm "T'EIEIENEFF afizioinm:

POSITION SHIP ROLL RAM TENSIONER RESULTING FROM HYPOTHETICAL UNCORRECTED FOR POSITION INVENTORS fi %5M 3 @W sesame METHOD AND APPARATUS FOR HiGHLINE TENSlGN QUNTBQL Ellis H. Born, Qolumhus, Peter B. Burnharn, Worthington, and Paul Wolfe, Dublin, @hio, assignors to Ahex Qorporation, New York, Fifth, a corporation of Delaware Continuation-lament of application Ser. No. 496,4tl8,

Get. :5, W65. This application Feb. 23, 15 67, Ser.

11 Claims. (Cl. 254-172) ABSTRACT (BE THE DHSELUSURE A method and apparatus for automatically and continuously maintaining a preset tension on the highline of a transfer system for transferring articles between two moving ships at sea.

Cross references to related application This application is a continuation-in-part of copending application Ser. No. 486,408, filed Oct. 15, 1965.

Brief summary of the invention In the transfer of articles between two moving ships at sea, it is customary to utilize one cable or so-called highline extending between the two ships to support a trolley while simultaneausly another cable or so called transfer line is used to control movement of the trolley over the highline. In our copending application Ser. No. 496,408, we have disclosed a completely automatic system for controlling the transfer cable during transfer or the trolley between the ships. The invention of this application concerns automatic control of the highline so that cable is payed out or taken in as required by the relative movements of the ships.

A highline cable normally extends from a cable winch on the supply ship, through a multiple wrap ram tensioner and over to the receiver slip to which it is attached. The ram tensioner comprises a multiple wrap block and tackle having one fixed pulley spaced from a second movable pulley, the two pulleys being biased apart by a spring or compressible element. Because of the several wraps, the ram holds approximately seventy feet of cable in reserve and available in the event that the ships separate by that distance or move together to that extent. This is suflicient capacity to handle normal roll and pitch of the two ships in relatively rough seas. However, if the ships should take diverging or converging courses, or if the ships should roll excessively, this capacity is insufficient and cable must be stripped from or taken in by the winch to compensate for these relative movements. Prior to this invention, this paying in or out of cable from the winches has always been handled by a seaman who watched the tensioning ram and when he thought it was too tight, caused the winch to pay out line, and when too slack, caused it to take in line. This method is at best haphazard and often resulted in broken and lost cable and trolleys.

This invention is predicated upon the concept of automatically controlling operation of the highline winch by monitoring the position of the ram tensioner which is a function of the tension of the cable and utilizing the monitored information to control the winch. In the preferred embodiment, the monitored information is converted into an electrical signal, the amplitude of which is a function of the ram tensioner position. This electrical signal is passed through a deadband filtering circuit operative to pass only signals of predetermined amplitude so States Patent 0 3,388,7 Patented June 11, 1968 that hunting or constant operation of the winch is avoided. From the filtering circuit, the signal is fed as an input into three parallel control circuits; a signal duration damping circuit, a very high position overide control circuit, and a position rate of change override control circuit. A signal passed by any of these three parallel circuits becomes a command signal to a servo control valve which in turn controls operation of a fluid pump and motor system operative to drive the highline winch.

The signal duration damping circuit functions to pass a command signal whenever it has persisted for a preset time interval, as for example 7 /2 seconds. This is approximately one-half of the normal roll cycle time for a supply ship so that this circuit operates to dampen out all signals resulting from the roll and pitch of the ships which can be handled without winch operation by the tensioning ram. If the ships should change to a diverging or converging course, this control circuit will pass a correction or a command signal to the servo control system after the signal has persisted for the preset time.

The position overide control circuit and the rate of position change override control circuits both function to protect the system against high rate, long duration cable tension and ram tensioner position changes which could break the cable or cause an accident if the condition persisted for the time interval required to operate the signal duration dampening circuit. The position override contol circuit comprises an amplitude discriminating circuit operative to pass only a signal indicating an unusually high or low ram tensioner position. The rate of change circuit measures the rate at which the ram tensioner position is changing and if excessive, passes a command signal to the winch control servo to immediately initiate operation of the winch.

The primary advantage of this highline control system is that it automatically controls highline tensioning while permitting the ram tensioner to handle the high frequency and low amplitude position changes. In this way wear and tear of the winch and winch control system, as well as power consumption is minimized.

These and other objects and advantages of this invention will become more readily apparent from the following description of the drawings in which:

FIGURE 1 is a diagrammatic illustration of a highline transfer system for transporting articles between a supply ship and a receiver ship,

FIGURE 2 is an electric-hydraulic diagrammatic illustration of the inventive highline winch control circuit of this application,

FIGURE 3 is a graph on which relative ship positions are plotted on a reference line basis, the solid sine wave illustrating a normal maximum ship roll rate and ampliplitude and two dashed output curves representing input and output to the integration control circuit,

FIGURE 4 is a graph on which relative ship positions are plotted on a reference line basis, the solid sine wave illustrating a normal maximum ship roll rate and ampli plitude and the two dashed curves representing uncorrected and corrected positions of the ram tensioner resulting from excessive rate of ram tensioner position change,

FIGURE 5 is a graph on which relative ship positions are plotted on a reference line basis, the solid sine wave form illustrating a normal non-sine wave rate and amplitude and the two dashed curves representing uncorrected and corrected high amplitude ram tensioner position.

Referring first to FIGURE 1, there is diagrammatically illustrated a conventional highline transfer system for conveying a trolley it) between a supply ship 11 and a receiver ship 12. This is just one of several difierent systems or methods of transferring articles between ships but is the one conventionally used whenever heavy loads are to be transferred. In accordance with this method, the trolley is suspended from and rolled over a highline 14 while a transfer cable 15 attached to the trolley 10 is payed out or taken in so as to maneuver the trolley between the ships. Conventionally, the transfer cable 15 extends from an inhaul winch 13 on the supply ship, over a pulley 16 on the supply ship, to a point of attachment 17 with the trolley. From the attachment point 17, the transfer cable 15 extends to and around a pulley 18 on the receiver ship, and back to an outhaul winch 19 on the supply ship. By properly maneuvering the inhaul and outhaul winches 13, 19 to pay out cable from one winch and take it in on the other, the trolley 10 may be conveyed between the ships. A completely automatic system for controlling the inhaul and outhaul winches so as to effect automatic transfer of the trolley between the ships is disclosed in our co-pending application Ser. No. 496,408.

The invention of this application concerns the automatic operation of the highline winch 20 so as to pay out or take in cable as required by the relative movements of ships as they are moved apart to together as a consequence of roll, pitch, yaw or varying courses between the two ships.

When completely rigged, the highline 14 extends from a drum of the highline winch 2d, beneath an idler pulley 29, through a tensioning ram 21, beneath another idler pulley 28, over a pulley 22, to a point of attachment 23 on the receiver ship. A pair of freely rotatable rollers or pulleys 24 attached to the trolley 10 ride over the highline 14, and support the weight of the trolley 1% from the highline.

The ram tensioner 21 is a conventional piece of nautical equipment and has, therefore, not been illustrated in detail. It comprises a stationary frame 39 upon which is rotatably mounted a multiple Wrap pulley 31 and a vertically movable and rotatable multiple wrap pulley 32. Generally, both pulleys 31, 32 support three wraps of cable so that the cable and pulleys 31, 32 act as a large block and tackle between the winch 20 and pulley 22.

Generally a hydraulic motor 34; (FIGURE 2) in cooperation with an air accumulator 35 biases the movable pulley 32 away from the stationary pulley 31. The cylinder 37 of motor 34 contains a fluid reservoir 38 beneath a piston 36 so that when the piston is forced down by the tension in the cable, fluid is forced from the reservoir into the air accumulator 35. Air entrapped in this accumulator is thereby compressed so that it acts as a large compression spring. Of course, a large metal spring could be substituted for the hydraulic motor and air accumulator.

In order to pay out or take in cable from the winch 29, it is driven by a fluid motor 41' through a gear reduction box 41. The motor in turn is driven by a servo controlled fiuid pump 42. As is conventional in such pumps, the servo or electrical motor 43 of this pump is operative to position the pump hanger in accordance with an electrical command signal from an amplifier 44. The actual position of the pump hanger is reflected by an electrical pct 45 operative to generate an electrical feedback signal which is returned to the amplifier 4-4 via a feedback lead 46. The output of the amplifier 44 is thus a ditlerential or error signal which is proportional to the difference between the command input signal and the feedback signal from the pct 45.

The winch 20 may be operated in either a manual or an automatic mode of control. In the manual mode, the command signal to the amplifier 44 is derived from the positioning of a manually controlled handle 43 operative to generate a signal which varies between -5 and +5 volts. The polarity of this signal controls the direction of Winch rotation and the amplitude determines the speed of winch operation. This input signal is fed into the pump control amplifier 4% via an electrical lead 49 through a normally closed contact RC-l of a mode control relay (not shown). So long as a differential in either polarity or amplitude exists between the command input on the lead it and the feedback. signal on lead 46, the resultant error output from the amplifier 44 continues to reposition the hanger of the pump 42. When the error is reduced to zero, the hanger position will be maintained and the speed and direction of rotation of the winch drum 24} will be maintained. Thus, in the manual mode of control, the winch drum 2% simply responds to the speed and direction command of the handle position. In the normal course of events, the manual control mode is used only during rigging of the cable between the ships. As soon as the rigging is complete and the highline cable 14 extends between and is attached to both ships, the control is switched to automatic operation by actuation of the control relay (not shown) so that a tension within a predetermined range is maintained on the highline.

In the automatic mode of control, the winch 20 maintains a predetermined average ram tensioner position irrespective of all ship movements. To this end, it pays out cable whenever the ram tensioners position exceeds a preset value and takes in cable whenever the ram tensioner is relaxed to too great an extent.

Upon actuation of the control relay (not shown) which switches the control from manual to automatic control, the normally closed contact RC4 is opened and a normally open contact RC-Z is closed. This results in the command signal to the amplifier 44 being derived from a transducer 53 attached to the ram 21 rather than from manual control of the handle 43. This transducer is operative to convert linear movement of the movable pulley 3.. into an electrical command signal. To this end the transducer comprises a mechanical arm indicated by a dashed line 52. in FIGURE 2, connected. to a wiper arm 74 of a potentiometer 75' operative to generate a position feedback signal of, varying amplitude whenever the position of the ram tensioner is different from the present value. If the tension in the cable 14 is relaxed, the pulley 32 moves away from the fixed pulley 31 with the result that the transducer 53 generates a positive voltage signal in a lead 56. Alternatively, if the tension in the cable exceeds the preset value, the pulley 32 is moved toward the fixed pulley 31 with the result that a negative polarity signal is generated in the lead 56.

The signal in lead 56 serves as an input to three parallel circuits to the command amplifier 44. These three circuits comprise a signal duration damping circuit, a position override control circuit, and a position rate of change override control circuit.

The signal duration damping circuit functions to dampen out any signal which has not persisted for a preset time interval, preferably about one-half the normal roll cycle time of the supply ship. in this way, the winch is precluded from rhythmically operating to pay out or take in line with each roll cycle.

The ram 21 has approximately feet of capacity and is capable of compensating for the roll of the two ships. Therefore, the signal duration damping circuit is included to avoid operation of the winch to compensate for errors which can be handled by the ram tensioner.

The position override control circuit functions as a safety circuit which operates the winch whenever the tension in the cable moves the ram tensioner outside a predetermined safety range, irrespective of the duration of the signal. In other words, this circuit operates to immediately initiate operation of the winch whenever the position of the ram tensioner goes beyond a safe operating range.

The position rate of change override control circuit similarly functions as a safety valve. It operates to im- .ediately initiate operation of the winch whenever it detects that the tension in the cable is changing at a rate which, if allowed to continue, would result in damage to the equipment.

In order to eliminate hunting or constant operation and reversing of the drive to the winch drum, the command signal from the transducer 53 is first fed through a tension amplitude discriminating circuit which comprises a pair of Zener diodes 57 operative to pass only signals which exceed plus or minus two volts. In other words, these Zener diodes block any signals in the range between +2 and -2 volts.

The signal duration damping circuit is essentially a ramp generator circuit. This ramp generator circuit 60 (enclosed by the dashed box 60a) comprises a high gain amplifier circuit 61 (enclosed by the dashed box 61a), a signal clamping circuit 62 (enclosed by the dashed box 62a), and an integrating circuit '63 (enclosed in the dashed box 63a). Amplifier circuit 61 is a conventional high gain amplifier operative to amplify any signal within the range of at least volts. The output from this amplifier is fed through the conventional clamping circuit 62 comprising a pair of Zener diodes 64, 65 connected in series. These Zener diodes clamp any signal of more than +6 volts or less than '6 volts. The output from this clamping circuit 62 is fed via lead 66 as an input into the conventional integrating circuit 63. The integrating circuit 63 comprises a conventional amplifier having a high capacitance feedback loop. The output of this integrating circuit 63 is fed as an input via lead 59 into an amplitude discriminating circuit 6*? and as a negative feedback signal via lead 73 back to the high gain amplifier circuit 61. Amplifier 61 clamps at :6 volts with a difference of :M; volts between leads 58 and 73. The discriminating circuit 67, which comprises a pair of series connected Zener diodes 68, 69, is operative to pass only signals outside a predetermined range, as for example, signals greater than +2 volts and less than 2 volts. From the discriminating circuit 67, the output signal is fed as an input into the pump command amplifier 44.

Referring now to FIGURE 3, there is represented graphically, on a distance versus time plot, the roll of the supply ship. As depicted by the dotted line 70, the roll normally varies from a center position to a distance of-approxirnately 30 feet and occurs during a time interval of seconds. In other words, the supply ship rolls from one extreme position to an opposite extreme position during approximately 7 /2 seconds. Superimposed on the same graph, is a plot 71 (depicted by a solid line) of a voltage versus time of the input signal to the integrating circuit 63. As may be seen in this graph, the input signal from the high gain amplifier 61 quickly builds up to a value of 6 volts and holds at this value as a consequence of being clamped by the clamping circuit 62. The out-put of the integrating circuit 63 is depicted by a dashed line 72 in FIGURE 3. As may be seen in this figure, the output is a ramp which slowly builds to a value of 2 volts after a time interval of 7 /2 seconds.

When the output signal of the integrating circuit 63 builds to the value of more than +2 volts or less than 2 volts, it is passed by the Zener diodes 68, 69 into the control amplifier 44.

The net effect of the ramp generator circuit 60 is to dampen out any feedback signal which has persisted for a time interval of less than 7 /2 seconds, one-half the normal roll cycle time of the supply ship. If the signal continues to build after 7 /2 seconds, as it does when the ships are on diverging courses, the output signal from the ramp generator builds to more than 2 volts and then is passed by the Zener diodes 68, 69 as an input into the control amplifier so as to result in operation of the winch.

The position override circuit 78 comprises a pair of Zener diodes 80, 81 connected in series in a circuit which parallels the ramp generator. These Zener diodes 80, 81 receive as an input the signal in lead 58 and operate to block any signal of less than predetermined amplitude, as for example, any signal in the range between +4 volts and 4 volts. Any signal passed by the Zener diodes S0, 81 serves as an input to a conventional amplifier 82, the output of which is fed via lead 83 as a command signal to the amplifier 44.

Any signal passed by the Zener diodes 80, 81 is an indication of a very high or very loW position of the ram tensioner. Consequently, the gain of amplifier 82 is sufficiently high to cause the pump 42 to go on full stroke or, otherwise expressed, to operate the winch at its maximum operating speed.

The operation of the position override control circuit 78 is depicted graphically in FIGURE 5. In this graph, the position of the ram tensioner which results from normal roll of the two ships is depicted by solid line 92. In the normal course of events, and assuming that the two ships are on parallel courses, the ram tensioner would never move a suflicient distance from the zero center line position to generate a position override signal greater than +4 volts or less than -4. However, it as depicted by the dashed line 93, the two ships converge a sufficient distance to enable the ram tensioner to move to a position which results in the generation of a signal of less than 6 volts, the line will go slack. Alternatively, if the ships part sutficiently to give rise to a ram tensioner position signal of more than +6 volts, the line will part or break. Before either of these alternatives occur, and as depicted by the dashed line 94, the position override control circuit '78 passes a signal through the Zener diodes 80, 81 to the amplifier 82 Which results in the pump 42 going on full stroke to operate the Winch to take in cable if the the value of the signal is less than +4 volts or to pay out cable if the value is more than +4 volts.

The position rate of change override control circuit 86 has the same effect of causing the pump 42 to go on full stroke whenever it detects that the position of the ram tensioner is changing at an excessively high rate. This circuit 86 comprises a conventional R-C circuit which receives as its input, the output of the ram tensioner feedback potentiometer 53 via lead 56. The output of the RC circuit 86 is fed as an input to an amplitude discriminating circuit comprising a pair of diodes 89, 9t) operative to pass only signals above a predetermined amplitude, as for example, +1 or 1 volt. Any signal passed by these diodes becomes an input to the amplifier -82 via a lead 91 and after being amplified, is fed as an input to the control amplifier 44 via lead 83.

FIGURE 4 illustrates graphically the operation of the position rate of change control circuit 86. So long as the slope of the line 95 representing movement of the ram tensioner resulting from ship roll does not exceed a predetermined value, there is no resulting signal passed by the R-C circuit -86. However, if the rate of movement of the ram tensioner suddenly changes, as depicted by the dashed line 96, the slope of the line changes and the R-C circuit passes a command signal to the amplifier 82, which results in the operation of the winch. Thus this circuit causes the winch to be immediately operative before the line can go slack or can be tensioned to the breaking point. As depicted in FIGURE 4, the winch is caused to operate and take in line before the line can go slack so that the corrected movement of the ram tensioner follows the dashed line 97 rather than line 96. It is to be noted that this correction is initiated by the rate of change control circuit 86 even before the ram tensioner passes through the zero or centered reference position so that the potential slack condition is detected very early and corrected before slack can develop.

In operation, the automatic control circuit is operative to measure the position of the ram tensioner and, if it exceeds a predetermined range, to command operation of the winch through one of the three parallel control circuits. The time damping circuit only passes a signal which persists for a time interval of 7 /2 seconds or more so that it averages out the normal position changes resulting from the roll of the two ships. If a signal persists for more than 7 seconds, indicating that the ships are on a relatively converging or diverging course, this damping circuit passes a command signal to the control amplifier 44 causing compensatory movement of the winch drum to pay out or take in cable as required to bring the ram tensioner back into the preset range.

If the position of the ram tensioner goes beyond the safe operating range, the output of the transducer will be of such magnitude as to be passed by the Zener diodes 80, 81 and 57 as an input to the amplifier 82, and from the amplifier 82, as a command to the amplifier 44. This position override signal then causes the pump to go up to full stroke and operate the winch up to rated speed until the measured position is back in the safe operating range.

Similarly, if the position rate of change measuring circuit 86 detects that the position is changing at a very high rate, the RC circuit will feed an input through the diodes 89, 90 as an input into the amplifier 82. The output of this amplifier is then fed as an input into the control amplifier 44 which also causes the winch to operate at speeds up to maximum speed until the rate of speed at which the position is changing is brought back into a safe range.

While only a single preferred embodiment of this invention has been disclosed and described herein, those skilled in the arts to which this invention pertains will readily appreciate numerous changes and modifications which may be made without departing from the spirit of our invention. Specifically, those skilled in this art will appreciate that there are hydraulic and mechanical equivalents of the electrical control circuits described hereinabove and that these equivalents may be substituted for the electrical controls to achieve the same results. Therefore, we do not intend to be limited except by the scope of the appended claims.

Having described our invention, we claim:

1. A control system for maintaining a preset tension upon a cable extending between two moving ships at sea, said cable extending from a winch drum on one ship, through a ram tensioner on the same ship, and over to the other ship,

said ram tensioner comprising a pair of spaced, multiple wrap pulleys over which said cable extends, said pulleys being mounted for movement relative to each other and being biased apart by a compressible element,

transducer means for generating an electrical signal having a characteristic which is a function of said compression and thus of the position of said ram tensioner,

an electrical control circuit having said electrical signal from said transducer as an input,

means including said electrical control circuit for operating said Winch so as to maintain a predetermined range of said rarn tensioner position, and

said control circuit including control means operative to dampen out short time duration position feedback signals so that said winch operating means only responds to a position feedback signal within a predetermined range after it has persisted for a predetermined time interval.

2. The control system of claim '1 which further includes a position override control circuit by-passing said control means to actuate said winch, operating means upon meas urement of a position of said ram tensioner above said predetermined range such that said winch operating means is responsive to a position change above said predetermined range irrespective of the time interval during which it is maintained.

3. The control system of claim 1 which further includes a position rate of change control circuit by-passing said control means to actuate said winch operating means in the event of a rapid position change of said ram tensioner so that said winch responds to a high rate of change of position or said ram tensioner irrespective of the time interval during which it occurs.

4. The control system of claim 1 wherein said predetermined time interval is at least equal to one-fourth the normal roll cycle time of said one ship but not more than the duration of a complete roll cycle for said ship.

5. A control system for maintaining a preset tension upon a cable extending between two moving ships at sea, said cable extending from a winch drum on one ship, through a ram tensioner on the same ship, and over to the other ship,

said ram tensioner comprising a pair of spaced multiple wrap pulleys over which said cable extends, said pulleys being mounted for movement relative to each other and being biased apart by a compressible element,

transducer means for generating an electrical signal having a characteristic which is a function of the position of the ram tensioner,

an electrical control circuit having said electrical signal irom said transducer as an input,

means including said electrical control circuit for controlling a servo controlled fluid pump, said pump being operative to drive a fluid motor which in turn drives said winch drum, said control circuit being operative to maintain the tension in the cable within an acceptable range, and

said control circuit including a ramp generator circuit in series with an amplitude discriminating circuit operative to dampen out large amplitude, short time duration, position feedback signals so that said winch operating means only responds to a position feedback signal within a predetermined range after it has persisted for a predetermined time interval.

6. The control system of claim 5 which further includes a position override control circuit by-passing said ramp generator circuit, said position override circuit comprising an amplitude discriminator circuit operative to actuate said servo controlled pump in response to a position feedback command above said predetermined range irrespective of the time interval during which it is maintained.

7. The control system of claim 5 which further includes a position rate of change control circuit by-passing said ramp generator operative to actuate said servo controlled pump in the event of a rapid position change in said ram tensioner so that said winch responds to a high rate of change of position in said ram tensioner irrespective of the time interval during which it occurs.

8. The control system of claim 5 wherein said prede termined time interval is at least three seconds but not more than the duration of a normal roll cycle for said one ship.

9. The method of maintaining a preset tension upon a cable extending between two moving ships at sea, which cable extends from a winch drum on one ship, through a ram tensioner on the same ship, and over to the other ship, said ram tensioner having a pair of spaced, multiple wrap pulleys mounted for movement relative to each other and biased apart by a compressible element, which method comprises generating an electrical signal having a characteristic which is a function of the position of the ram tensioner,

using said characteristic of said electrical signal to control said winch drum so as to maintain a predetermined range of tension in said cable, and

damping short duration characteristic changes in said electrical signal so that said winch responds only to a position feedback signal within a predetermined range after it has persisted for a predetermined time interval which is at least as long as one-fourth the characteristic roll cycle time of said one ship.

10. The method of claim 9 which further includes the step of utilizing said electrical command signal to oper- Q 10 ate said winch at any time said position feedback signal References Cited exceeds said predetermined range such that said Winch is UNITED STATES PATENTS responsive to a position above said predetermined range irrespective of the time interval during which it is main- 3,150,860 10/1964 Nelson 254-172 tamed. 5 3,309,065 3/1967 PrudHomme 254-472 @3331; $3 iiii iifnial i ii nii ii i 222?? iii? FOREIGN PATENTS P g p 315,176 2/1934 Italy.

winch drum at any time said signal exceeds a preset rate of change so that said winch responds to a high rate of change of position of said ram tensioner irrespective of 10 EVON BLUNK P'lmary Exalmner' the time interval during which it occurs. H. C. HORNSBY, Assistant Examin

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