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- Type of Document: M.Sc. Thesis
- Language: English
- Document No: 47432 (58)
- University: Sharif University of Technology, International Campus, Kish Island
- Department: Science and Engineering
- Advisor(s): Salarieh, Hassan; Khayyat, Amir Ali Akbar
- Abstract:
- Control of line of sight (LOS) orientation is a fundamental prerequisite for virtually all dynamic applications in which an optical sensor is used to obtain images. In this research, a 3 DOF parallel mechanism is utilized to build a stable platform for high precision satellite photography. The platform may be designed based on the Stewart platform concept. The stability is obtained by controlling the roll, pitch and yaw of the mechanism. To apply linear control techniques and to use roll-pitch and yaw rates and also their absolute values, an active stable platform is designed. Line Of Sight (LOS) is a position vector from origin of a topocentric-horizontal system to the satellite of interest. The principal coordinate systems used in tracking the LOS, and the transformations between these different coordinate systems, are summarized in this research. These are primarily Cartesian (orthogonal) coordinates, and the transformations between them can be represented by orthogonal matrices. All representations such as ECI, ECEF, NED, and LHLV coordinate frames are usually utilized in the derivation of equations and calculation of the reference signal for the active stable-platform controller in the satellite. The positions of satellites are determined with six Keplerian orbital parameters. A body will be a satellite in a circular orbit around the Earth that has enough velocity in the horizontal line. So that the centrifugal force balances the centripetal force produced by the gravitation attraction of the Earth. Since the Earth is not a round sphere in reality, the deviations of the orbit of satellite rom an ellipse which corresponds to Kepler’s laws will emerge. Our goal is to control the LOS vector of a camera mounted on a Stewart platform within a satellite. So the dynamics equations of a Stewart platform on a satellite constrained to move in an orbit and able to rotate freely by its actuators that should be extracted. The LOS vector should be determined by the orbital motion dynamics of the satellite. This vector is used as a reference signal for the controller of the Stewart platform. Therefore, it can be said that LOS vector is a desired output for the control system and the length of every pod of the Stewart platform and also the satellite orientation and position are the input signals to it. In this research, at first, capabilities and characteristics of 3-RPS Parallel mechanism such as available workspace, its kinematics and dynamics are examined; then a spot on the earth surface is considered as a target of photography. The shooting is performed by three similar satellites that move on the orbital paths in which they have different inclination angles. Finally, it is necessary to analyze the results such as timing and accuracy of shooting
- Keywords:
- Parallel Robot ; Satellites ; Control ; Vector Control ; Photography
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محتواي کتاب
- view
- Chapter 1 Introduction
- Chapter 2 An Introduction to Orbital Coordinates
- Chapter 3 3-RPS Parallel Robot
- Chapter 4 Dynamic Modeling
- Chapter 5 Desired Trajectory
- Chapter 6 Control of Parallel Robot
- 6.1 Introduction
- 6.2 Leg model
- 6.3 Trajectory generation
- 6.4 PID controller
- 6.5 Position control
- 6.6 To complete solution of represented example 1
- 6.7 Accuracy of Shooting
- 6.8 Torques and Forces
- 6.9 Calculation of Saturation Time
- 6.10 Energy Consumption
- 6.11 Reaction wheel
- 6.12 To solve a representative example 2
- 6.13 To representative example 3
- Chapter 7
- Appendix A
- References
- چکیده