Chapter 1 Introduction Introduction
7.1 Accomplishments and Contributions
7.2 Future Works ... 149
7.1 Accomplishments and Contributions
This thesis presented a new spherical motion platform and control and operation systems for the platform. The control systems dealt with parametric uncertainties and time delay, including experiments to verify the proposed theories. In addition, human factors were analyzed to evaluate the operation of the proposed motion platform with humans. Five specific contributions are achieved as follows:
• Development of Novel Six DOFs Spherical Motion Platform
The unique design for the six DOFs spherical motion platform with the novel spherical wheel was proposed. The spherical wheel generated omnidirectional motion perpendicular to each other, composed of active and free rolling. From that, the cockpit sphere could achieve unlimited rotational as well as translational motions.
The mathematical modeling, including kinematics and dynamics, was analyzed for the two designs, SMP I and II. The SMP I has three spherical wheels, the minimum number to drive cockpit spheres, whereas four spherical wheels for the SMP II with symmetric design and simplified kinematics.
Moreover, in SMP II, the compliant spherical wheel mechanism was presented to achieve full rolling contact between the cockpit sphere and small spheres. The SMP could achieve unlimited rotational motion, but the translational motion depended on the motion range of linear stages. Therefore, the translational workspaces for the SMP I and II were analyzed, and the results were compared by applying
146
geometric stability defined by the eccentric margin. The comparison showed that the SMP II has better geometric stability and a larger translational workspace than SMP I.
The coupled rotation occurs from the translation occurs due to smooth motion and characteristics of the omnidirectional wheel. Thus, the coupling effect was quantitatively analyzed and was compensated by the proposed ADC exactly. In SMP II, the kinematic control was presented to make full rolling contact, minimizing slipping in the contact. Moreover, the slip observer estimated the slip ratio, and from that, the kinematic controller could deal with the slipping.
Non-contact orientation sensing methodology was proposed by multi-sensor fusion and integration strategies. The optical sensing system for orientation measurement was developed with a compliant mechanism (including three passive joints) to maintain uniform sensing distance during operation.
Sensor fusion between IMU and optical sensors utilizing KF provides accurate and reliable orientation measurements. In addition, a loadcell sensor was applied to measure cockpit distributed weight and further the CG of the cockpit sphere.
• Robust Control System for Parametric Uncertainties
The robust control system was proposed as DOB-SMC and adaptive SMC for the SMP driven by spherical wheels capable of providing unlimited rotation along all axes for a flight simulator.
The uncertain kinematics (distorted cockpit sphere, surface contact, slipping, etc.) was estimated from the disturbance observer, and the SMC was then applied for dynamic uncertainties and disturbances (unknown inertia, gravity, friction, etc.). The finite-time convergence in the presence of uncertainties was proved for the DOB-SMC. The numerical simulation results demonstrated the tracking performance for the DOB-SMC compared to the PID control and I-SMC.
The experimental results validated better position and orientation tracking control performance of the proposed controllers despite dynamic uncertainties and kinematic uncertainties compared to the conventional controllers. In addition, the experiments verified tracking control performances, including flight maneuvers (phugoid and dutch roll modes) and unlimited rotation. As a result, it is demonstrated that the SMP can be utilized as a flight simulator for VR. In particular, it can help a pilot training flight skills in emergencies such as a helicopter with a malfunction of the tail blade, aircraft recovery from a stall.
• Robust Control System for Input Time Delay
The PPC was presented to compensate for the time delay and disturbance effects in the operation of the SMP. The state prediction was designed with the DOB and the modified strategy. The implementation of predicted disturbance on the SP and controller improved the tracking performance and enhanced robustness against disturbance. Moreover, the predictor-based preview method was applied to estimate future reference trajectory for preview control, and finally, it led the controller to
147
minimize the tracking error. Numerical simulation and experimental results verified the feasibility of the proposed controller for implementation to the motion platform. The improved prediction method was compared to the existing validating improved tracking performance. In addition, it was demonstrated that the PPC with state prediction could make the state converge to zero. Finally, it is expected that the proposed controller can be implemented to various virtual reality industries sensitive and vulnerable to delay effect.
• Operation System With Human Factors
The human factors were analyzed for the SMP operation how the SMP improves ride quality for the operators. The effectiveness of motion simulators in VR was verified by analyzing human factors, motion sickness and sense of realism. The motion simulator reduced the mismatch between motion and visual cues. The experimental results showed that the motion simulator could decrease motion sickness and increase realism due to motion cues compared with the no-motion group, where the visual cue was only provided to the operators. As a result, analyzed human factors will help researchers design optimized operation and control systems of motion simulators for humans.
• Practical Implementation
In the engineering area, experimental verification of the proposed mechanism and algorithm is one of the most critical parts to increase the feasibility and validity of the proposed. The proposed theories and mechanisms were verified from experiments for the perspective on the practical implementation. It shows the high research impacts for this thesis and further demonstrates the feasibility of proposed novel motion platforms as well as control and operation systems. Moreover, all developed mathematical models and control algorithms were validated from the full-scale SMP I and II.
148 Figure 7.1. Achievements of the proposed research.
149