Omnidirectional mobile robots have been popularly employed in several application areas. However, the kinematics and singularity analysis for these systems have not been clearly identified, especially for the redundantly actuated case, which is common in current omnidirectional mobile robots. In light of this fact, this article introduces two different kinematic approaches for a typical omnidirectional mobile robot having three caster wheels, and examines singularity configurations of such systems. Then, a singularity‐free load‐distribution scheme for a redundantly actuated three‐wheeled omnidirectional mobile robot is proposed. Through simulation, several advantages of the redundantly actuated mobile robot (singularity avoidance, input‐load saving, and exploiting several subtasks) are presented. © 2002 Wiley Periodicals, Inc.

A new parallel-type gripper mechanism is proposed in this work. This device has a parallelogramic platform that can be flexibly folded. Therefore, this mechanism not only can be used to grasp an object having irregular shape or large volume, but also can be utilized as a micro-positioning device after grasping objects. Forward position analysis and platform kinematics are investigated to deal with motion tracking and force control. Kinematic optimization is performed to design a parallel-type gripping mechanism so that it can reach the specified workspace, span the given range of the specified configuration parameters, and generate a desired force to grasp an object. A pneumatic rotator is employed for actuation and a miniaturized proportional 4/3-way directional valve is specially developed to deal with feedback-based dynamic control. The proportional valve allows indirect force control by measuring the offset-load pressure raised by the contact between the grasped object and the parallel platform. In experimental work, the performance of the motion tracking and indirect force control has been shown to be successful.

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Closed-form forward/reverse position solutions for a 6-degree-offreedom (DoF) parallel mechanism that has some type of nonsymmetric geometry are derived in this study. Particularly, the derived forward-position analysis is applicable to the mechanisms in which three passive joints are constrained to move parallel to the moving plate. Its kinematic and dynamic characteristics are investigated via isotropic index of the Jacobian matrix and isotropic index of the output effective inertia matrix, respectively. From this investigation, it is found that the mechanism has fairly uniform kinematic/dynamic characteristics throughout its workspace. To examine the effectiveness of the proposed 3-PPSP-type mechanism, a prototype is designed, implemented, and tested experimentally under various operating conditions. A simple PID controller is applied to the system, and its joint positions are servo-controlled. The controlled system showed a good trajectory performance. Noting that a more advanced controller requiring a forward-and/or reverse-position solution can be applied to the system in real time, it can be contended that the manipulator is a candidate for the high-precision manipulator.

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This work deals with motion planning algorithms of an omni-directional mobile robot with active caster wheels. A typical problem occurred in the motion control of such omni-directional mobile robot, which has been identified through experimental experiences, is skidding of the mobile wheel. It sometimes results in uncertain rotation of the steering wheel. To cope with this problem, a motion planning algorithm which resolves the skidding problem and uncertain motions of the steering wheel is mainly investigated. For navigation of the mobile robot, the posture of the omni-directional mobile robot is initially calculated using the odometry information. Then, the accuracy of the mobile robot's odometry is measured through comparison of the odometry information and the external sensor measurement. Finally, for successful navigation of the mobile robot, a motion planning algorithm that employs kinematic redundancy resolution method is proposed. Through simulations and experimentation, the feasibility of proposed algorithms was verified.

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