Abstract Constant line tension can be maintained in a ship''s mooring or towing line extending from a winch by supplying to a polyphase phase-wound induction motor driving the winch alternating current from an alternating-current source the frequency of which is variable in response to the load on the winch. Such variablefrequency source may be an alternator driven by a phase-wound induction machine powered to operate as a motor. The variablefrequency AC source is connected to the winch motor to drive the winch only in the reeling-in direction, but the tension on the line can retard the motor speed or stall the motor or rotate the winch and motor in the opposite, paying-out direction against the reeling-in driving torque of the motor. The winch motor torque can be adjusted by varying the value of resistance shunted across the rotor winding of the winch motor. The line can be retrieved very quickly by having a squirrel-cage alternating-current motor connected mechanically to the phase-wound induction machine. During constant-line-tension operation, such motor is simply idly rotated with such machine, but for rapid line retrieval the motor can be powered by the same AC supply as powers the phase-wound induction machine and such motor will then drive the phase-wound induction machine positively. The winch-motor torque can be adjusted by varying the value of resistance shunted across the rotor winding of the winch motor. Also, for towing applications the voltage of the variable-frequency source can be altered in response to variations in the length of line paid out or reeled in to control the winch motor in turn in response to sensing the extent of rotation of the winch drum in paying out or reeling in the towing line and correspondingly varying the field excitation of the alternating-current generator supplying current to the winch motor to operate the winch motor for restoring the line to its original length.
In line-tensioning mechanism including line-winding means connected to a towing line, an electric line-winding means motor continuously connected to supply continuous mechanical torque to the line-winding means for winding in such line whenever the mechanical torque on the line-winding means produced by the line tension tends to drop below the mechanical torque produced on the line-winding means by the line-winding means motor, an alternator connected to supply alternating electric current to said linewinding means motor continuously for producing continuous mechanical torque on the line-winding means tending to reel in line whether said line-winding means motor is stopped or is turning in the line-reeling-in direction or is turned in the line-paying-out direction by the winding means resulting from tension in the towing line, load-responsive means responsive to the electric load on said alternator resulting from the mechanical torque produced by said line-winding means motor on the line-winding means and operable to vary an electrical output characteristic of said alternator automatically in response to variation in mechanical torque exerted by said line-winding means motor on the line-winding means resulting from changes in towing line tension and corresponding variation in electric load on said alternator, variable-resistance means adjustable for altering the speed of said alternator and consequently an electric output characteristic of the power supplied by said alternator to said line-winding means motor for altering the torque of said motor on the line-winding means, line-length-sensing means connected to the line-winding means and to said variable-resistance means and always operable automatically in response to paying-out rotation of the line-winding means to effect adjustment of said variableresistance means for increasing the speed of said alternator and thereby increasing the torque of said line-winding means motor on the line-winding means and increasing the towing line tension gradually and progressively without interruption rather than abruptly as the towing line is paid out, tending to reel in the towing line.
Claim 2
Dependent Claim
312 words
In line-tensioning mechanism including line-winding means connected to a towing line, an electric line-winding means motor continuously connected to supply continuous mechanical torque to the line-winding means for winding in such line whenever the mechanical torque on the line-winding means produced by the line tension tends to drop below the mechanical torque produced on the line-winding means by the line-winding means motor, an alternator connected to supply alternating electric current to said linewinding means motor continuously for producing continuous mechanical torque on the line-winding means tending to reel in line whether said line-winding means motor is stopped or is turning in the line-reeling-in direction or is turned in the line-paying-out direction by the winding means resulting from tension in the towing line, load-responsive means responsive to the electric load on said alternator resulting from the mechanical torque produced by said line-winding means motor on the line-winding means and operable to vary an electrical output characteristic of said alternator automatically in response to variation in mechanical torque exerted by said line-winding means motor on the line-winding means resulting from changes in towing line tension and corresponding variation in electric load on said alternator, variable-resistance means adjustable for altering the speed of said alternator and consequently an electric output characteristic of the power supplied by said alternator to said line-winding means motor for altering the torque of said motor on the line-winding means, line-length-sensing means connected to the line-winding means and to said variable-resistance means and always operable automatically in response to paying-out rotation of the line-winding means to effect adjustment of said variableresistance means for increasing the speed of said alternator and thereby increasing the torque of said line-winding means motor on the line-winding means and increasing the towing line tension gradually and progressively without interruption rather than abruptly as the towing line is paid out, tending to reel in the towing line.