Optimization Of The Mechanical Design Of The Dual Axis Inertially Stabilized Platform For The Line Of Sight Stabilization

For the purpose of stabilizing the Line Of Sight (LOS) of Electro-Optical (Eo) surveillance and tracking system, a Dual Axis Inertially Stabilized Platform (ISP) is required to isolate the LOS from the carrier disturbances. Due to the maneuver of both the target and the observer, The LOS is misdirected instantaneously, which requires the presence of an ISP to null theses rotational disturbances and maintains the LOS of the EO devices stable and directed to the target. The orthogonal dual axis ISP is the minimum required set of ISPs to achieve the efficient stabilization. Generally, for the purpose of directing the LOS, two methods are commonly used; the Mass Stabilization and the Mirror Stabilization.Based on The Mass Stabilization method, this research was aiming to design a high performance, small size and light weight3D Scanner consists mainly of a Laser Range Finder (LRF), a Complementary Metal-Oxide-Semiconductor (CMOS) camera, Pilot green laser, two electronic Compasses and rate gyro to obtain the range, Azimuth and Elevation angles for each point in the Field of View (FOV). The ISP structure consists of the inner gimbal that carrying the EO devices and rotates in the Elevation direction about the Y-axis, and the outer gimbal that makes the cross elevation rotation (Azimuth) about the Z axis. The designed ISP carrying these EO devices has achieved Azimuth range of±120°, Elevation range of-10°：+190°, with angular rates and accelerations of200°/s and100°/s2respectively in both directions, Bandwidth of100Hz, and resolution of0.9μradian. The Electro-Mechanical system’s design process implements many disciplines and requires the integration of different design facilities to assure the optimal system’s design. The design was dynamically optimized based on the Finite Element Method (FEM) Modal Analysis. The weight of the payload carrying frame was decreased by35%and the1st torsional mode of vibration was increased by22%of the original design. Moreover, the overall dynamic performance of the inner gimbal was optimized and the dynamic performance improved by75%. The results declare that the FEM Modal Analysis is an effective tool to optimize the system’s dynamic performance to assure the optimal working conditions are sitting far from the resonating failure. The Kinematics and dynamics models were discussed in details to facilitate understanding the precession of the ISP, as well as. to simulate the designed system to assure the ability of the system to act diligently according to the maximum designed requirements. This work not only gives the mathematical model for the two-axis ISP, but the more important is that it gives the methodology to derive and analyze it, to direct the design toward optimality. Additionally, the designed controller has achieved high robustness, zero steady state error, fast response, minimum overshoot and minimum settling time. The importance of taking advantage of the strengths of each individual design facility has been declared trough the integrating the3D solid Modeling, Mathematical Modeling, FEM Analysis, and Computer Simulation in a continuous feedback process to achieve the optimal design of the ISP. As an application of the designed ISP, a Laser Detection and Ranging (LADAR) system has been designed and implemented to facilitate mobile targets path tracking and terrestrial scanning of large objects. The design simplicity, low cost of the system and the ability of building such systems by researchers in laboratory were the key features for this work. The LADAR system was loaded on two-axis orthogonal rotary table, and consists of LRF, control unit, remote control unit, optical imaging system (camera and optical telescope), two electronic compass, green pilot laser, power unit, communication unit, portable computer, power supply, cables and connectors. The interface for the system is acquired using the LabVIEW software, where each point is depicted by a distance, Azimuth rotation angle and Elevation rotation angle in a spherical coordinate system with respect to the origin of the LRF sensing lens. The system architecture and the mathematical modeling for the data manipulating were discussed in details along with the results of the field experiments.On the other hand, based on the Mirror stabilization method, the design results of a Fast Steering Mirror (FSM) have reached a Bandwidth of1kHz, resolution of0.04μradian, angular acceleration of16×103rad/s2, an optical rotational angle of±2mille radian, maximum angular velocity of8radians/s, with a clear elliptical optical aperture of2×3inch. The FSM system architecture, mirror structure, compliant mechanisms’ design, and actuators’ selection were discussed in details. Nevertheless, a general discussion for the FSM system enhancement was introduced for further optimization processes.Moreover, this research has established a new concept for the LOS stabilization that combines the advantages of both classical systems and avoids their weakness points, that we call "Ball Stabilization". It permits the angular rotations of the EO devices in the Azimuth and Elevation direction inside a spherical enclosure without the need of gimbals for each direction. The system was designed to simulate the human’s eye shape and rotation behavior inside its cavity, where the tension of the muscles makes nearly pure rotation about the two axes orthogonal to the LOS-axis with their origin fixed in the eye’s center. This new system implements piezoelectric edge actuators which are strictly connected to the payload and together perform the combined angular rotations inside the spherical enclosure. The elimination of gimbals reduces the size and inertia forces of the system, which facilitates the achievement of high resolution, angular rates and accelerations. For proofing this concept, an ISP system was designed and simulated to have a FOV of±30°in both directions, band width of1552Hz, resolution of1×10-50angular rate of210°/s, angular acceleration of24×103°/s2, within a compact size of130mm in diameter, and total weight of1.19kg.Finally, this work has presented a real Ball Stabilization Opto-Electro-Mechanical ISP system design, manufacturing and integration process that has an outer diameter of220mm and can achieve the required stabilization about the Elevation and Azimuth directions by rotating the payload on the inner surface of the ball. This real system has achieved another two degrees of freedom by applying four driven rolling rings on the outer surface of the ball to rotate the ball itself, which achieved additional stabilization about the Elevation and Roll axes.