Patent Number: 
Section: claims

1. A system for attitude control of an underwater vehicle comprising:an underwater vehicle that includes a thruster;an assist device that is coupled to said underwater vehicle with a cable and includes cable handling equipment and a thruster;a cable attachment-to-attachment distance arithmetic operation unit that detects a distance between a cable attachment of said underwater vehicle and a cable dispenser, serving as a cable attachment, of the assist device; anda control unit that stores the relationship between the cable attachment-to-attachment distance and cable length including a predetermined amount of slack and determines the amount of cable to be wound up or let out based on said cable length associated with said detected cable attachment-to-attachment distance. 2. The system for attitude control of the underwater vehicle according to claim 1,wherein said assist device includes a depth finder of said assist device and an image acquisition unit that acquires images of an upper surface of said underwater vehicle,said underwater vehicle includes a depth finder of said underwater vehicle and a plurality of light emitting devices on the upper surface of a hull thereof, andsaid cable attachment-to-attachment distance arithmetic operation unit determines said cable attachment-to-attachment distance based on water depth data from said depth finder of said assist device and said depth finder of said underwater vehicle and said captured images, said images including images of said light emitting devices and being input from said image acquisition unit. 3. The system for attitude control of the underwater vehicle according to claim 2,wherein said assist device and said underwater vehicle include an inclinometer of said assist device and an inclinometer of said underwater vehicle, respectively,said cable attachment-to-attachment distance arithmetic operation unit further comprising:a relative depth arithmetic operation unit that determines vertical distance between said cable attachments based on a difference between water depth data from said depth finder of said assist device and water depth data from said depth finder of said underwater vehicle;a relative horizontal-distance arithmetic operation unit that determines horizontal distance between said cable attachments by obtaining a difference between a tilt angle from said inclinometer of said assist device and a tilt angle from said inclinometer of said underwater vehicle and performing rotation correction on said captured images including said light emitting devices with said differential tilt angle; anda relative distance/yaw angle arithmetic operation unit that determines said yaw angle from said cable attachment of said underwater vehicle to said cable dispenser of said assist device and said cable attachment-to-attachment distance based on said vertical distance and horizontal distance between the cable attachments. 4. The system for attitude control of the underwater vehicle according to claim 1,wherein said assist device includes a sonar transmitter having a plurality of crystal resonators arranged in a two-dimensional matrix,said underwater vehicle includes a sonar receiver that receives ultrasound from said sonar transmitter, andsaid cable attachment-to-attachment distance arithmetic operation unit determines said cable attachment-to-attachment distance based on the results of transmission and reception of the ultrasound between said sonar transmitter and said sonar receiver. 5. The system for attitude control of the underwater vehicle according to claim 1,wherein said assist device includes a laser transmitter and said underwater vehicle includes a laser receiver, andsaid cable attachment-to-attachment distance arithmetic operation unit determines said cable attachment-to-attachment distance based on the results of transmission and reception of the laser between said laser transmitter and said laser receiver. 6. The system for attitude control of the underwater vehicle according to claim 1,wherein said control unit further comprising:a cable length table lookup unit that includes a cable length table storing said relationship between said cable attachment-to-attachment distance and cable length including a predetermined amount of slack and extracts a cable length associated with said detected cable attachment-to-attachment distance from said cable length table; anda cable length storing unit that stores a current cable length obtained concurrently with operation of said cable handling equipment, wherein said control unit determines said amount of cable to be wound up or let out by comparing said extracted cable length with said current cable length. 7. The system for attitude control of the underwater vehicle according to claim 2,wherein said control unit further comprising:a cable length table lookup unit that includes a cable length table storing said relationship between said cable attachment-to-attachment distance and cable length including a predetermined amount of slack and extracts a cable length associated with said detected cable attachment-to-attachment distance from said cable length table; anda cable length storing unit that stores a current cable length obtained concurrently with operation of said cable handling equipment, wherein said control unit determines said amount of cable to be wound up or let out by comparing said extracted cable length with said current cable length. 8. The system for attitude control of the underwater vehicle according to claim 3,wherein said control unit further comprising:a cable length table lookup unit that includes a cable length table storing said relationship between said cable attachment-to-attachment distance and cable length including a predetermined amount of slack and extracts a cable length associated with said detected cable attachment-to-attachment distance from said cable length table; anda cable length storing unit that stores a current cable length obtained concurrently with operation of said cable handling equipment, wherein said control unit determines said amount of cable to be wound up or let out by comparing said extracted cable length with said current cable length. 9. The system for attitude control of the underwater vehicle according to claim 4,wherein said control unit further comprising:a cable length table lookup unit that includes a cable length table storing said relationship between said cable attachment-to-attachment distance and cable length including a predetermined amount of slack and extracts a cable length associated with said detected cable attachment-to-attachment distance from said cable length table; anda cable length storing unit that stores a current cable length obtained concurrently with operation of said cable handling equipment, wherein said control unit determines said amount of cable to be wound up or let out by comparing said extracted cable length with said current cable length. 10. The system for attitude control of the underwater vehicle according to claim 5,wherein said control unit further comprising:a cable length table lookup unit that includes a cable length table storing said relationship between said cable attachment-to-attachment distance and cable length including a predetermined amount of slack and extracts a cable length associated with said detected cable attachment-to-attachment distance from said cable length table; anda cable length storing unit that stores a current cable length obtained concurrently with operation of said cable handling equipment, wherein said control unit determines said amount of cable to be wound up or let out by comparing said extracted cable length with said current cable length. 11. A method for attitude control of an underwater vehicle, the method being performed by a system including said underwater vehicle with a thruster and an assist device coupled to said underwater vehicle with a cable and including cable handling equipment and a thruster, the method comprising:detecting a distance between a cable attachment of said underwater vehicle and a cable dispenser, serving as a cable attachment, of said assist device;referring to a cable length table storing the relationship between cable attachment-to-attachment distance and cable length including a predetermined amount of slack to extract a cable length associated with said detected cable attachment-to-attachment distance; andcontrolling operation of said cable handling equipment based on the amount of cable to be wound up or let out associated with said extracted cable length.