Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-08-24
2004-03-30
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S628000, C073S633000, C600S447000
Reexamination Certificate
active
06711953
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method of and an apparatus for controlling the direction of transmitting and receiving beams produced by a cylindrical transducer used in an ultrasonic fish-finding apparatus.
A sonar system like an ultrasonic fish-finding apparatus is usually installed on a vessel which rolls and pitches in operation. A transducer of the sonar system swings with pitching and rolling motions of the vessel. A fish-finding apparatus is a device which transmits ultrasonic pulses from a transducer, receives return echoes reflected by underwater targets such as fish schools, and visualizes the received echoes on a display screen. Accordingly, if the transducer swings under the influence of the pitching and rolling of the vessel, an on-screen picture also sways in synchronism with the swing motion of the transducer, making it impossible to determine the direction or depth of a target. It might even be impossible to obtain target echoes on the screen if the swing motion is extremely severe.
Under this circumstance, it has long been desired to develop a beam-stabilizing control method which makes it possible to cancel out the influence of swing motion and constantly form transmitting and receiving beams in desired directions such that underwater targets including fish schools can be located in a stable fashion regardless of pitch and roll of a vessel.
Such a beam-stabilizing control method has not been developed yet however. A main reason for this is as follows. If it is intended to just tilt a beam produced by a cylindrical transducer formed of transducer elements arranged in rows and columns by conventional technology, it is only necessary to control the phases of carrier signals of the individual rows of the transducer elements. In order to stabilize the beam against the swing motion (rolling and pitching), however, it is necessary to control the carrier phase of each transducer element in the individual rows, and this requires the same number of phase control circuits as the number of the entire transducer elements. If the cylindrical transducer is formed of 20 rows of 30 elements arranged in a ringlike form, for example, a total of 600 phase control circuits are needed. The beam-stabilizing method has not been developed yet despite a pending demand, because it results in complication and a significant increase in the physical size of hardware.
Although the duration of each transmitting pulse is extremely short compared to the period of a vessel's pitching and rolling (swing motion of a transducer), reception of return echoes is a noticeably time-consuming process. Provided that a sonar system is operated on a 3000 m range, for example, reception of return echoes derived from a single transmitting pulse takes approximately 4 seconds. Since pitch and roll angles continuously vary during this period, it is necessary to restablize the beam to compensate for the varying pitch and roll angles during the reception of echo signals. If the tilt angle is varied during the reception of echo signals, however, continuity of the phase of the echo signals is lost at the point of change in the tilt angle, and this results in an inability to produce a beam properly.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the invention to provide a method of and an apparatus for stabilizing the direction of transmitting and receiving beams produced by a cylindrical transducer by compensating for swing motion of the beams due to pitching and rolling of a vessel with a simple construction.
According to the invention, a method of controlling the direction of a transmitting beam and a receiving beam formed by a cylindrical transducer which is constructed of a plurality of ultrasonic transducer arrays arranged in a circular form comprises the steps of dividing the ultrasonic transducer arrays in a plurality of groups, and controlling the direction of the beams formed by the ultrasonic transducer arrays depending on which group the individual ultrasonic transducer arrays belong.
In one aspect of the invention, the phases of carrier signals fed into individual elements of the ultrasonic transducer arrays are controlled depending on which group the ultrasonic transducer arrays belong.
Let us now assume that the cylindrical transducer forms a beam having a full-circle umbrellalike pattern directed obliquely downward by a tilt angle a. If the cylindrical transducer is inclined by the angle of inclination b in a particular direction due to pitching and rolling of the vessel, the inclination of the beam in that direction becomes &agr;+&bgr; while the inclination of the beam in the opposite direction becomes &agr;−&bgr;, making it impossible to sound underwater situations with a uniform tilt angle in all directions. To compensate for the inclination of the cylindrical transducer, the tilt angle of the beam formed by the cylindrical transducer is adjusted to &agr;−&bgr; in its inclining direction and the tilt angle of the beam is adjusted to &agr;+&bgr; in the opposite direction. If the tilt angle of the beam is corrected in this manner, it is possible to sound the underwater situations with a uniform tilt angle a in all directions regardless of the inclination b of the transducer. A cylindrical transducer typically includes 20 to 30 vertical transducer arrays arranged in a circular form. This structure of the cylindrical transducer may be regarded, in other words, as vertically stacked ringlike arrays, each including 20 to 30 ultrasonic transducer elements. Controlling the phases of carrier signals fed into the individual transducer elements results in considerable complication in hardware configuration. To avoid this inconvenience, the vertical transducer arrays arranged in the circular form are divided into multiple groups and the direction of the beams are controlled depending on which group the individual transducer arrays belong in this invention. This approach makes it possible to stabilize the beams with required accuracy by use of a least complicated configuration.
According to the context of this invention, the cylindrical structure of the transducer as claimed in the appended claims includes not only a circular cylinder but also other shapes, such as truncated circular cones, whose top and bottom have different diameters.
In another aspect of the invention, the aforementioned step of controlling the direction of the beams includes the steps of detecting the angle of inclination of the cylindrical transducer, and controlling the direction of the beams formed by the ultrasonic transducer arrays of the individual groups to compensate for the angle of inclination of the cylindrical transducer.
Since the cylindrical transducer is fixed to the bottom of the vessel, it swings in accordance with pitching and rolling motions of the vessel. If a sensor for detecting the angle of inclination of the cylindrical transducer is provided, it becomes possible to stabilize the transmitting and receiving beams by detecting the angle of inclination of the cylindrical transducer and controlling the direction of the beams to compensate for the angle of inclination of the cylindrical transducer.
Compared to the period of the vessel's pitching and rolling motions (which is at least one second), transmission pulse length is considerably short. It is possible to assume that there are no variations in the angle of inclination of the cylindrical transducer during a transmission cycle (where the transmission pulse length is 100 ms at the maximum) and, therefore, it is sufficient to compensate for the swing motion of the transmitting beam using the angle of inclination detected immediately before transmission. In other words, it is not necessary perform successive operations for compensating for the varying angle of inclination during each transmission cycle.
Operation during a reception cycle differs from that in the transmission cycle, however. Duration of the reception cycle is determined as a function of soun
Hayashi Tatsuo
Ishihara Shinji
Matsuhiro Norio
Birch & Stewart Kolasch & Birch, LLP
Furuno Electric Company Ltd.
Larkin Daniel S.
Miller Rose M.
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