레이저 자이로스코프의 구동시 발생하는 센서 오차의 보상 방법에 관한 연구

Abstract

Inertial sensors have been used as suitable inertial instruments for navigation, guidance, and attitude controls. Electromechanical inertial sensors have generally dominated the guidance, navigation and control applications since the dawn of inertial sensing technology. But, because they have the problems of mechanical wear, friction and production cost to accuracy, they are replaced with the optical inertial sensor. Most of them essentially have the sensor errors in the operations and for the high accuracy of sensors, the scale-factor errors should be compensated. The optical inertial sensors should be treated by the compensation methods of sensor errors in the operation of optical rotation sensor. In principle of operation, when the resonator cavity is rotated, there is a difference in the path length for two counter propagating beams that the counterclockwise beam may find the mirrors approaching and so has less distance to travel than the clockwise beam which sees the mirrors moving away. Combining two output beams, we can see an interference pattern which is modulated by a beat frequency proportional to the rate of rotation. Therefore, their accuracy as very sensitive sensors is limited by the optical-mechanical characteristics due to frequency coupling between two counter-propagating waves in the resonator cavity, at the input rotation rates. The unstable performances due to the path length in the cavity, frequency biasing or a dead-band in the frequency ranges will produce scale-factor errors of sensors. This frequency coupling gives no phase difference, and no an angular increment is detected. For the accuracies of optical sensors, the elastic bimorph piezoelectric actuators have been used. Their applications are for the dead-band region of optical rotation sensor and the path length control in a ring cavity where they prevent undesirable optical ray paths resulting from thermal or mechanical deformations, and for the avoidance of dead band at low rotation rates which can affect the scale-factor error. For the optical compensations of sensor errors, the piezoelectric actuators are used for the avoidance of lock-in threshold and path length control of optical ray, and the trajectories of optical ray transfer in the resonator should be predicted and corrected for the manufacturing misalignments of TRP (total reflective prims) and thermal expansions of the configurations components in the resonator. This paper presents the design consideration for the dynamic and static behaviors of the elastic bimorph piezoelectric actuators, and an optical ray transfer trajectories due to the manufacturing misalignment and thermal expansions of the configuration components. In order to describe such important design parameters of piezoelectric actuators as the peak dither rate, quality factor and resonant frequency of mechanical dither and the piezoelectric actuating deformation for the path length control, the simple cantilever and circular plate structures are developed and parameterized in the geometric parameters and material properties. Especially, the material properties include the mechanical and piezoelectric properties of piezoelectric element and non-piezoelectric element. Measured quality factor and relative angular velocity were found to be limited by the working temperature and bonding fabrications. The geometric parameters and material properties can be represented for the estimation of the mechanical characteristics such as torsion stiffness, bending profile, stress caused by bending of the spokes, peak dither rate and resonant frequency. Analytical results indicate that the electric loading term to the piezoelectric layer appears in the static displacement expression, depending on either the manner in which the plate is supported, or the geometric parameters bonded to the non-piezoelectric layer. The presented solutions can serve a design tools for determining the design parameters of piezoelectric actuators. In the optical ray trajectory in the ring cavity, the principal operation of an optical rotation sensor depends on the phase difference for the counter-propagating waves within a closed path. The reflecting mirrors mounted on the monoblock form the traveling waves. The manufacturing accuracy of monolock influences the traveling path of ray, the sensitivity of laser resonator for misalignments, and diffraction losses. 3 x 3 ray transfer matrix was derived for the optical components with centering and squaring errors in a ring resonator, which can be utilized to predict the optical ray paths on the basis of the manufacturing errors of monoblock as well as the misalignment of mirrors under the operating environments. Then the distance and orientation (or slope) at the arbitrary plane inside the resonator along the ideal optical path can be calculated from the chain multiplication of the ray transfer matrix for each optical component in one round trip. The manufacturing misalignments of optical sensors also show that the counter-propagating rays in a ring resonator with errors does not coincide in each round trip, which results in gain difference between two beams and how these errors can be adjusted through the alignment procedure. 3 x 3 ray matrix formalism for the manufacturing tolerances of TRP (total reflective prisms) and optical path length under the operating environments of the ring resonator can be used to calculate the beam size and its displacement from the optical axis and the deviation at the diaphragm. Most of laser gyroscopes would expect it to produce a constant Sagnac frequency with stability at the available frequency level. With some sensor corrections applied, the time series of the measured rotation rate smoothes out. Excellent measurements of rotation rates are obtained for the reduction of lock-in effect and geometric scale-factor variations, notwithstanding a gain medium.