Compass is a primary magnetic compass, which is one of the four great inventions in ancient China. During the Tang and Song Dynasties, China's overseas trade was very developed. Large merchant ships sail to the Persian Gulf, the Red Sea and other places, and their shipbuilding and navigation technology ranks among the top in the world. The earliest record of compass used in navigation can be found in Zhu Yu's Pingzhou Tan in the Northern Song Dynasty (1 1 19). The book says: "A boatman knows geography, but he looks at the stars at night, the sun during the day and the compass at dusk." A compass used for navigation is also called a compass. In the Ming Dynasty, the bronze water compass marked 24 directions with the names of eight branches, twelve branches and four-dimensional hexagrams (Figure 2). It is generally believed that the compass spread from China to Arabia and then to Europe, but it is controversial. According to legend, at the beginning of14th century, F. Gioia, an Italian from South amalfi, first connected the paper compass card (steering wheel) with the magnetic needle to rotate. This is a leap in the development of magnetic compass. From then on, when the ship changes direction, it is no longer necessary to turn the compass by hand. /kloc-in the 6th century, Italian Kalden made a balance ring to keep the magnetic compass level when the ship was shaking. /kloc-at the beginning of the 0/8th century, an Englishman, E. Harry, made the world's first equal magnetic difference curve.
After the appearance of the iron ship, the magnetic compass deviated. Prior to this, the phenomenon of self-deviation had been described in Fang Yizhi's Essentials of Physics in the late Ming and early Qing Dynasties. The book talks about the interference of iron on the magnetic needle and the reason why ships don't use nails: "The salty seawater is also harmful to magnetism." /kloc-in the first half of the 9th century, Ye Ying nationals M. flinders and G. B. Airy successively put forward methods to eliminate deviation, and French Poisson made contributions to the mathematical theory of deviation. 65438+In 1970s, the British physicist W. Thomson made a stable compass and installed it in a compass cabinet with a modern deviation corrector, which was once used as standard equipment by the British Navy. At the beginning of the 20th century, it was made of a liquid compass with more stable performance and less friction between shaft pins, and now it has been used by most ships. Gyro compass can be divided into mechanical pendulum type and electromagnetic control type according to the way of applying torque to gyro.
① Mechanical pendulum gyro compass: According to the way of generating pendulum moment, it can be divided into two types. One is a single-rotor heavy mercury compass with elastic support, or a liquid connector compass (Figure 6), such as a sperry gyro compass; The other is to put the center of gravity of the gyroscope below the support center, which is called the downward weight compass (Figure 7), such as Anschuetz double-rotor downward weight compass supported by liquid floating. The pendulum moment produced by these two methods is in opposite directions, and the vector direction of momentum moment is also in opposite directions. The moment of momentum vector leading to the liquid-connected compass, and the moment of momentum vector of the downward-weighted compass points to the north. Under the action of pendulum moment, the northern end of the main shaft of the mechanical pendulum compass will swing around the meridian plane with equal amplitude, and its trajectory is an ellipse on the spherical surface. For the mechanical pendulum compass with damper, the north end of the main shaft tends to the meridian plane in the form of damping oscillation, and is stable relative to the meridian plane, thus providing the true north reference.
The sensitive part of liquid communication compass is composed of gyro motor and bracket, suspended by steel wire, and the control torque is generated by the negative pendulum effect of mercury device. The sensitive part of the down-weight compass is a sealed gyro ball, in which two gyro motors, a lamp holder and a damper are installed, and the parameters are the same (Figure 8). The two gyro motors are vertically supported on the lamp-shaped bracket, connected with the spring through a crank connecting rod, and form an included angle of 45 degrees with the north-south line of the spindle of the gyro ball respectively. With this device, two gyro motors can only rotate around their respective vertical axes in opposite directions and at the same angle at the same time, but the rotation angle is very small. Therefore, the moment of the momentum vector synthesized by them is always consistent with the north-south line of the spindle of the gyro ball, which is similar to the action of a single rotor. Using two gyro motors can effectively reduce the swing error. ② Electromagnetic control gyro compass: An electromagnetic control device consisting of an electromagnetic pendulum and a torque device is installed on the structure of a two-degree-of-freedom balanced gyro, and the gyro compass (Figure 9) applies control torque to the gyro through electrical signals, which is referred to as electronic control gyro compass for short. Because the electric signal is easy to control, the control torque can be changed as needed to realize the rapid stability of the compass. Ama-Brown compass is a typical electromagnetic control compass. CLP- 1 gyrocompass made in China is an electromagnetically controlled gyrocompass used in civil ships (see color map). The most common gyro devices in mechanical gyrocompass and electric control gyrocompass are ball gyro and liquid floating gyro. After the emergence of liquid floating gyro, flexible gyro has been developed. Its support system adopts flexible joints instead of traditional gyro frame bearings. Flexible gyro has the advantages of simple structure, small volume, light weight, long life and high reliability, and has been applied in ships. Flexible gyro compass still belongs to electronic control compass in principle. Gyro compass has latitude error, speed error, impact error, swing error and baseline error. There is latitude error in vertical axis damping gyro compass, which is a principle error. The speed error has nothing to do with the structural parameters of the compass, but with the speed, course and latitude of the ship. Latitude error and speed error are regular, which can be corrected by looking up the table, moving the baseline or dial and torque compensation. When the ship is maneuvering, the impact error caused by the influence of inertia force on the gyro compass can be eliminated by cutting off the damper to make the constant amplitude swing period of the compass equal to 84.4 minutes or cutting off the electromagnetic pendulum. Gyro compass has a device to reduce the rocking error caused by ship rocking, so this error can generally be ignored. The baseline error caused by improper installation of the main compass or the compass baseline is a fixed error. After measurement, the base of the main compass or the minute compass can be rotated to make the baseline parallel to the fore and aft lines of the ship for correction. In a calm sea, when the ship is sailing at a constant speed and direction, the error of the corrected compass should not be greater than 1.