Research into omnidirectional mechanisms have contributed in the development of highly maneuverable robot platforms in recent years. These are characterized by their ability to enable motion without being constrained by the non-holonomic constraints of a conventional differential drive based mobile robot platform. The effective utilization of an omnidirectional robot, in highly dynamic environments such as robot-soccer, requires an effective control strategy apart from trajectory planning. In this regard, dynamic control and inverse dynamic control schemes control the system through the forces and torques generating the reference acceleration, the advantage being that the reference acceleration can be generated instantly. They are less affected by disturbances and allow predictable and tunable error dynamics. In most approaches however, wheeled mobile robot systems are typically modeled with an ideal rolling constraint, where the wheels are assumed to roll without slipping. However, rolling conditions are often violated while the platform is accelerating or decelerating, resulting in a non-zero slip that can cause navigational error. Omnidirectional robots such as the Omnibot, presented in this thesis, are particularly susceptible to large errors due to slip. Previous works in omniwheel based mobile robots often neglected the full import of these considerations in the development of different control schemes. Subsequently, in this thesis, the relevant dynamical theory, is first developed to explore the effects of slip for an omnidirectional mobile robot platform using omni-wheels. The dynamics approximate the traction forces at work with a nonlinear slip model widely used in the field. The resulting nonlinear equations of motion for the omniwheel platform using the Euler-Lagrange dynamic formulation are generated and are transformed to slip-space where the stability and steady state slip models of the slip dynamics are examined. From the analysis of the slip dynamics, at steady-state, slip is observed to be depend on the applied torque. This relationship has been assumed to be linear in this thesis, allowing the development of a Steady-state Slip rolling mode Inverse Dynamic Control (SSIDC) strategy. The performance of the proposed controller is verified through detailed simulations as well as real experiments on the OmniBot, and is compared with that of an Ideal Rolling mode Inverse Dynamic Control (IRIDC) strategy, for various motion tasks. The results indicate that the proposed control strategy (SSIDC) is effective for the task of high performance control of omnidirectional robots.
전방향(omnidirectional) 이동 메커니즘은 기존의 이동 로봇이 사용하는 차동 구동(differential drive) 방식과는 달리 non-holonomic 제약 조건 없이 자유롭게 이동 가능한 특징을 가지고 있다. 따라서 로봇 축구 등과 같은 동적인 환경에서 본 논문에서 사용된 OmniBot과 같은 전방향 이동 로봇이 효과적인데, 이를 위해서는 효과적인 제어 기법이 필요하다. 본 논문에서는 정상 상태 미끄럼 구름 모드(steady-state slip rolling modes)를 이용한 전방향 로봇의 비선형 역동역학 제어 기법을 제안한다. 바퀴에서 발생하는 견인력(traction force)을 근사하는 비선형 미끄럼 동역학 모델이 로봇 동역학에 적용되고, 로봇의 운동 방정식은 오일러-라그랑지안 방법을 통해 얻어진다. 유도된 운동 방정식은 미끄럼 동역학의 분석이 용이한 미끄럼 공간(slip space)으로 변환되어 사용된다. 정상 상태 미끄럼 모드 분석에 통해 본 논문은 정상 구름 상태에서 미끄럼과 토크 사이에 선형적인 관계가 있음을 가정한다. 이 가정은 본 논문에서 제안한 \`정상 상태 미끄럼 구름 모드 역동역학 제어(SSIDC, Steady-state Slip Rolling Mode Inverse Dynamic Control)\`에 이용된다. 제안한 제어의 효율성은 시뮬레이션과 OmniBot을 통한 실제 실험을 통해서 증명된다. 그리고 이상적인 구름 회전을 가정한 \`이상적 구름 회전 역동역학 제어(IRIDC, Ideal Rolling Inverse Dynamic Control)\`와 비교하여 실험하였다. 실제 실험 결과는 본 논문에서 제안한 SSIDC 방식이 전방향 이동 로봇의 고성능 제어에 효과적임을 보여준다.
