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Mechanical and Control System Design Enhancements for Stability and Safety of WMR Systems Against Environmental Disturbances

Tahami, Reza | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50411 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Vosoughi, Gholamreza; Meghdari, Ali
  7. Abstract:
  8. Hospitals are considered to be environments for employing social robots. However, it is necessary to provide conditions for the operation of these robots in such environment. Factors such as slippery and sloping surfaces, as well as the risk of falling robots from impact by the patient or other factors, cause the performance of these robots in these environments to be difficult. Friction and slip is a challenge posed by the path tracking mission in the hospital environment for these robots. In this regard, one of the objectives of this project is robot control to track the path on the surfaces in the event of a slip. The robot studied in this project is omnidirectional robot including Omni-wheel. Omni-wheels, while creating a holonomic movement, increase the slip that can challenge the track. In this regard, in order to get closer to the reality of the situation, a more precise model of the robot's motion is used. The strategy adopted in the trajectory tracking is that by considering friction and slip as the term of uncertainty in the robot model, a sliding mode controller is designed that is resistant to the specified uncertainties. Also, this controller executes the kinematic command of path following maneuver. The efficiency of this controller has been proven, according to the concept of Lyapunov, and finally, simulations have been performed to check the performance of the controller. The results of a series of simulations show that the performance and precision of this method depend on two-speed factors related to the path following maneuver. In order to conduct a tracking test on the robot and because of the slip of the wheels during the move, the current dead-reckoning methods are not appropriate in these conditions. For this reason, a robot positioning mechanism was designed and constructed. Another goal of the project is to protect the robot and prevent its reversal in the hospital environment due to accelerated movement (such as acceleration on sloping surfaces) and blows. Therefore, controlling robot stability and robot equilibrium analysis under various kinematic conditions is another goal of the project. In order to investigate and analyze the equilibrium and stability of a three-wheel robot, the concept of zero momentum point has been used and a three-phase strategy has been proposed. In the first phase, the effects of robot movements in different conditions on robot stability have been investigated. In the second phase, a controller was designed to stabilize the robot in case of overturning conditions (when the robot was placed on two wheels) and simulations were performed to validate the controller. In the third phase, a mechanical system for the robot is designed to act as a backup mechanism if the control system is not able to stabilize the robot. Finally, the experimental results of the tests on Robot Doctor Arash, located at the robotic pole, are designed to check the performance of the designed control systems
  9. Keywords:
  10. Path Following ; Stability ; Friction ; Omnidirectional ; Zero Moment Point (ZMP) ; Three-wheeled Robot ; Slippy Surface

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