21 октября 2018г.
In this article, we will consider different types of gyroscopes according to their classification based on design and operating principles.
1. Classification
1.1 Mechanical gyroscopes
A rotor gyroscope is distinguished among the mechanical gyroscopes - a rapidly rotating solid body whose axis of rotation can freely change the orientation in space. The speed of rotation of the gyroscope is much higher than the speed of rotation of the axis of rotation. The main property of such a gyroscope is the ability to preserve the invariable direction of the axis of rotation in space in the absence of influence on it of moments of external forces and to effectively resist the action of external moments of forces. This property is largely determined by the magnitude of the angular velocity of the gyroscope's own rotation.
This property was first used by Foucault in 1852 for an experimental demonstration of the Earth's rotation.
Due to this demonstration the gyroscope got its name from the Greek words "rotation", "observe".
1.2 Vibrating gyroscopes
A vibrating gyroscope is a device for determining the angular velocity of an object, containing vibrating parts that react to the rotation of the object. There are vibrating gyroscopes of rod and rotor type. In a rod type, some vibrating masses are a sensitive element, for example, rods like the branches of a tuning fork. One of the rod-type vibrating gyroscope, which has received practical application, is called a gyrotron. Its sensitive element is a vibrator consisting of rods, an elastic torsion bar connecting the base with a vibrator, a plate firmly fixed with a torsion and moving in a field of coils fastened on the base. Branches of the vibrator-tuning fork are driven into vibration motion with the help of a special electric circuit. If the object rotates around the axis together with the base of the vibrator with angular velocity w V, then a moment of Coriolis of inertia forces arises, which causes torsional vibrations of the vibrator around the axis. In this case, the plate oscillates between the coils. The amplitude of the oscillations is proportional to the angular velocity wV. The value of wV is measured from the coils with radio engineering methods. The device has some advantages: the lack of cardan suspension, rotating and rubbing parts; the presence of a single axis of sensitivity; linearity of indications; high reliability. The principle of operation of the rotor vibration gyroscope is similar, but instead of the rods and plates, the vibrating element is a rotating rotor with elastic suspension. However, the creation of this gyroscope is associated with a number of technical difficulties. The opportunities of using a gyroscope are very varied. The device is most simply used as a measure of the angular velocity of an object. Vibrating gyroscopes can also find application in gyroscopic stabilization systems, in inertial navigation systems and other areas of gyroscopic engineering.
Varieties
• Gyroscope at MAKS 2009
• Piezoelectric gyroscopes
• Solid-state wave gyroscopes. The work of one of the types of solid-state wave gyroscopes developed since the 80's. GE Marconi, GE Ferranti (WB), Watson Industires Inc. (USA), Inertial Engineering Inc. (USA) Innalabs, and others are based on the control of two standing waves in a physical body-resonator, which can be both axisymmetric and cyclically symmetric. In this case, the axisymmetric shape of the resonator makes it possible to achieve the characteristics of the gyroscope, namely: significant increase the lifetime of the gyroscope and its impact resistance, which is critical for many stabilization systems. In that way, standing waves are oscillations of an elliptical shape with four antinodes and four nodes located along the circumference of the edge of the resonator. The angle between adjacent nodes is 45 degrees. The elliptical shape of the oscillations is excited up to a certain amplitude. When the gyroscope turns around the sensitivity axis, the resulting Coriolis forces acting on the elements of the vibrating mass of the resonator excite a pair of oscillations. The angle between the main axes of the two modes is 45 degrees. A closed control loop (compensatory feedback) extinguishes the pairwise oscillation mode to zero. The amplitude of the force (that is the signal proportional to the current or the electric voltage in the compensation feedback circuit), necessary for this, is proportional to the angular velocity of the sensor rotation. The corresponding closed-loop control system is called compensatory. Piezoelectric elements fixed on the resonator are used to generate the compensating force and to read the induced motions. Such an electromechanical system is highly efficient and provides a low noise level of the output signal and a wide measurement range required for many "tactical" applications (although it reduces the sensor sensitivity in proportion to the expansion of its measurement range). Note that these gyroscopes use modern alloys of the Invar type with soldered piezoelectric elements of input- output or piezoceramic resonators with the burning of electrodes. In any case, their quality factor is theoretically limited to values of the order of 100 thousand (in practice, usually, not more than 20 thousand), which is much lower than the multi-millionth quality factor of quartz glass resonators or single crystals used for "strategic" applications.
1.3 Two-stage gyroscope
Many gyroscopic instruments use a simplified, two-stage version of the gyroscope, in which the outer frame of the three-stage gyroscope is eliminated, and the semi-axes of the internal gyroscope are fixed directly to the walls of the body, firmly connected with the moving object. If in such a device a single frame is not limited in any way, the moment of external force relative to the axis connected to the body and perpendicular to the axis of the frame will cause the axis of the rotor's own rotation to continuously precess away from this initial direction. Precession will continue until the axis of proper rotation is parallel to the direction of the moment of force, that isin a position where the gyroscopic effect is absent. In practice, this possibility is eliminated due to the fact that the conditions are set at which the rotation of the frame relative to the body does not exceed the limits of a small angle. If the precession is limited only by the inertial reaction of the frame with the rotor, then the angle of rotation of the frame at any time is determined by the integrated accelerating moment. Since the moment of inertia of the frame is usually relatively small, it responds too quickly to forced rotation. There are two ways to eliminate this negative side.
Opposing spring and viscous damper. Angular speed sensor. The precession of the axis of rotation of the rotor in the direction of the angular momentum vector directed along the axis perpendicular to the axis of the frame can be limited by a spring and a damper acting on the axis of the frame. The axis of the rotating rotor is fixed in a frame perpendicular to the axis of rotation of the latter relative to thehousing. The input axis of the gyroscope is the direction connected with the base, perpendicular to the axis of the frame and the axis of the rotor's own rotation with an non-deformed spring.
The moment of external force relative to the reference rotor rotation axis applied to the base at a time when the base doesn't rotate in the inertial space and therefore the axis of rotation of the rotor coincides with its reference direction causes the axis of rotation of the rotor to precess towards the input axis, so that the angle of deflection of the frame begins to increase. This is equivalent to applying the moment of force to the opposing spring, what is the important function of the rotor, which in response to the appearance of the input torque of the force creates a torque moment relative to the output axis. With a constant input angular velocity, the output torque of the gyroscope's force continues to deform the spring until the moment of force created by it, acting on the frame, causes the axis of rotation of the rotor to precess around the input axis. When the speed of such a precession, caused by the moment created by the spring, is equal to the input angular velocity, the balance is reached and the angle of the frame ceases to change. Thus, the angle of deflection of the gyroscope's frame allows to view the direction and angular velocity of rotation of the moving object.
