Previous isotropy analysis of a caster wheeled omnidirectional mobile robot (COMR) has been made under the assumption that the steering link offset is equal to the caster wheel radius. Nevertheless, many practical COMRs in use take advantage of the steering link offset different from the wheel radius. This paper presents a systematic isotropy analysis of a fully actuated COMR with variable steering link offset, which can be considered as the generalization of the previous analysis. First, with the characteristic length introduced, the kinematic model of a COMR is obtained based on the orthogonal decomposition of the wheel velocities. Second, the necessary and sufficient conditions for the isotropy of a COMR are examined to categorize three different groups, each of which can be dealt with in a similar way. Third, the isotropy conditions are further explored to identify four different sets of all possible isotropic configurations. Fourth, the expressions of the isotropic characteristic length required for the isotropy of a COMR are obtained.

This paper investigates the optimal isotropic characteristics of a caster wheeled omnidirectional mobile robot under full actuation. First, with the characteristic length introduced, the kinematic model is obtained based on the velocity decomposition. Second, the algebraic conditions for the isotropy are derived, from which two isotropic configurations are identified along with the required isotropic characteristic length. Third, the local and the global isotropy indices are examined to determine the locally and the globally optimal characteristic lengths. Finally, with prior knowledge of the isotropic configurations, the problem of determining the optimal initial configuration of a moving COMR is discussed

The omnidirectional mobility of a mobile robot loses significance in motion control, unless the isotropy characteristics of the mechanism is maintained well. This paper investigates the local and global isotropy of an omnidirectional mobile robot with three caster wheels. All possible actuations with different number and combination of rotating and steering joints are considered. First, the kinematic model based on velocity decomposition and the algebraic conditions for the local isotropy are obtained. Second, the geometric conditions for the local isotropy are derived and all isotropic configurations are fully identified. Third, the global isotropy index is examined to determine the optimal parameters in terms of actuation set, characteristic length, and steering link length.

This paper presents a complete isotropy analysis of an omnidirectional mobile robot with three caster wheels. All possible actuation sets with different number and combination of rotating and steering joints are considered. First, the kinematic model of a caster wheeled omnidirectional mobile robot (COMR) having n (3 /spl les/ n /spl les/ 6) actuated joints is obtained without matrix inversion. Second, with the characteristic length introduced, the isotropy conditions of a COMR are derived, which are imposed on two Jacobian matrices. Under the isotropy condition on one Jacobian matrix, three caster wheels should be identical with the length of the steering link equal to the radius of the wheel. Third, depending on the selection of actuated joints, the isotropy conditions on the other Jacobian matrix are examined. The isotropic configurations of a COMR are identified, along with the isotropy loci in the configuration space.

This paper presents the quantitative and geometric analysis on the kinematics of a wheeled mobile manipulator as the serial connection of a mobile platform and a manipulator. Three different modes of operation are considered, including two standalone operations of a mobile platform or a manipulator and one simultaneous operation of two subsystems. First, the well-defined directional manipulability measure of a robot is formulated. Second, the kinematic model of a mobile manipulator is derived and the configuration dependent singularity is analyzed. Third, the directional manipulability of a mobile manipulator is quantified and the effect of serial cooperation is analyzed. Finally, some discussions and conclusion are made.

For an anthropomorphic robot, this paper presents the optimal attachment of bi-articular muscles for improved stiffness generation As the optimal criteria, the maximal dynamic range of the coupling joint stiffness and the reduced semi-degeneracy in stiffness generation are considered The attachment of bi-articular muscles is optimized to determine the muscle spacing, the muscle count, the muscle combination, and the muscle size. Efforts are expended to make the optimization to be simple and effective resorting to geometrical reasoning.

This paper presents the analysis of an anthropomorphic robot as an active variable stiffness generator, with emphasis on the degeneracy in stiffness generation. First, the attachment of mono-/bi-articular muscles are optimized to maximize the dynamic ranges of the self and the coupling joint stiffness. Based on the geometric interpretation of the joint stiffness, a simple and effective way of determining the optimal muscle attachment is presented. Next, the cause of the semi-degeneracy in stiffness generation is identified as the sign inconsistency of the actual and the desired coupling joint stiffness. Using the configurational dependency of the actual coupling joint stiffness, the semi-degeneracy map over the entire joint space is obtained. Simulation results are also given.

This paper presents the optimal redundant actuation of closed-chain mechanisms for robotic applications requiring a high degree of operational stiffness, as well as the balance of force applicability and dexterity. First, by taking into account the distribution of active joints, the statics and the operational stiffness of a closed-chain mechanism are formulated with the analysis on the effects of actuation redundancy. Second, for given joint torque limit, task force, allowable disturbance, and allowable deflection, the task execution conditions of a closed-chain mechanism are derived along with the efficient testing formulas. Third, to achieve high stiffness while maintaining dexterity, the active joint distribution and the internal joint torque of a closed-chain mechanism is optimized. Finally, the simulation results for the optimal redundant actuation of a planar closed-chain mechanism are given.

Presents the smooth joint actuation switching in a closed chain mechanism for achieving high task adaptability. First, the kinematic characteristics of a closed-chain mechanism possibly with actuational redundancy is formulated, and the effect of the distribution of actuating joints is analyzed. Next, with respect to the task compatibility in control efficiency or accuracy, the joint actuation switching of a closed-chain mechanism is optimized, and the discontinuity in joint torque incurred due to the abrupt joint actuation switching is described. Then, the smooth transition in joint actuation of a closed-chain mechanism is proposed, based on the redundancy resolution associated with the augmented statics defined for a short transition interval. Simulation results for a planar closed-chain mechanism are given.

Presents a simple and effective way of improving the task adaptability of redundant open/closed chain mechanisms based on joint locking/unactuation and continuous joint mode conversion. The joint locking/unactuation in an open/closed chain mechanism is incorporated in the kinematics/statics of the mechanism, and the varying kinematic characteristics depending on the distribution of frozen/passive joints is analyzed. The discontinuity in joint velocity/torque of an open/closed chain mechanism, incurred when the joint mode switching is done abruptly, is described. Two methods of the continuous joint mode conversion for a short transition interval are proposed and compared. Finally, simulation results for a planar redundant open chain mechanism employing joint locking are given.

This paper presents the adjustment of the manipulability of a closed-chain mechanism using joint freezing/releasing and joint unactuation/actuation, leading to the improved task adaptability. A closed-chain mechanism under consideration consists of multiple redundant subchains and individual joints can be put into frozen, actuated or unactuated mode, as needed. First, the joint freezing and joint unactuation allowed for a closed-chain mechanism are examined, which limits the possible combinations of joint modes. Second, the kinematics of a closed-chain mechanism is formulated, taking into account joint freezing and joint unactuation. Third, the manipulability ellipsoids of a closed-chain mechanism with/without joint freezing and/or joint unactuation are defined and compared. Finally, the wide range of the manipulability of a closed-chain mechanism due to the changes of joint modes is exemplified.

This paper presents the analysis of the operational quality of redundantly actuated parallel manipulators. Two types of the actuation redundancy of a parallel manipulator are considered, which are introduced by replacing passive joints with active ones and by adding limbs. The operational quality of a parallel manipulator with/without actuation redundancy is quantified in terms of force applicability and operational stiffness. The effects of the two types of the actuation redundancy on the operational quality of a parallel manipulator are analyzed and compared. Both types of the actuation redundancy are shown to improve the operational stiffness as well as the force applicability, but in quite different ways. With such differences fully understood, it is possible to best utilize the actuation redundancy for a parallel manipulator with high force applicability and high operational stiffness.

This paper presents an in-depth analysis on the kinematic features of parallel manipulators, such as deficiency, singularity, and redundancy. Parallel manipulators under consideration are of a general form, with no restriction on their structure. Three orthogonal instantaneous motion spaces (IMSs) of a parallel manipulator are identified including deficient, uncontrollable, and controllable IMSs. Based on the IMSs, the deficiency and singularity of a parallel manipulator are devised and analyzed and their remedies are devised. Three types of redundancies of a parallel manipulator are introduced including the redundancies in serial chain, joint actuation, and parallelism. The three types of redundancies are shown to overcome the singularity of a parallel manipulator, as well as to improve either its dexterity or load capacity.>

This paper presents an in-depth analysis on the kinematic features of parallel manipulators, such as deficiency, singularity, and redundancy. Parallel manipulators under consideration are of a general form, with no restriction on their structure. Three orthogonal instantaneous motion spaces (IMSs) of a parallel manipulator are identified, including deficient, uncontrollable, and controllable IMSs. Based on the IMSs, the deficiency and singularity of a parallel manipulator are described and analyzed, and their remedies are devised. Three types of redundancies of a parallel manipulator are introduced, including the redundancies in serial chain, joint actuation, and parallelism. The three types of redundancies are shown to overcome the singularity of a parallel manipulator, as well as to improve either its dexterity or load capacity.>

This paper presents a unified and efficient method of solving the inverse kinematics for six degree-of-freedom serial connections of two three degree-of-freedom serial and parallel manipulators. Based on the kinematic analysis of three degree-of-freedom serial and parallel manipulators, the forward kinematics are formulated for six degree-of-freedom serial connections, including parallel-parallel, serial-parallel, parallel-serial, and serial-serial types. A unified method of solving the inverse kinematics for the serial connections is established: for a given task velocity, the inverse kinematics of two arms are obtained separately, thereby significantly reducing a computational cost. This is made possible by projecting a given velocity onto the infeasible velocity space of one arm independently. Through computational analysis, the proposed method is shown to be effective for the serial connections having at least one parallel manipulator.

This paper presents two different ap- proaches of deflning the manipulabilities and resistivi- ties of serial-parallel manipulator systems. In the flrst approach, the manipulability (resistivity) of the serial- parallel structure is dehed by imposing the kinematic constraint on the local manipulabilities (local resistiv- ities), each of which is obtained from the unit sphere in the joint velocity Ljoint torque) space of an individ- ual arm. In the second approach, the manipulability (resistivity) of the serial-parallel structure is defined by imposing the kinematic constraint directly on the unit sphere in the extended joint space formed by all the arms. The two approaches are shown to be com- plementary to each other: the fist approach is useful for the geometrical analysis of the interactions among local arms, while the latter is useful for the quanti- tative analysis of the performance of a serial-parallel structure as a whole.

An approach to a self-reconfigurable manipulator system which dynamically changes its topology according to given task requirements is presented. The proposed self-reconfiguration differs from that of conventional reconfigurable robots, in that it does not need to replace and reassemble modularized links to build a robot of desirable mechanical structure, but it customizes a multiple redundant manipulator system by reconfiguring its mechanical structure through serial, parallel, and bracing mechanisms of multiple arm cooperation. The authors present a methodology of generating serial, parallel, and bracing structures for a self-reconfigurable dual-arm system based on manipulabilities and resistivities. Such manipulabilities and resistivities quantify the efficiency and capability of a self-reconfigurable dual-arm system in generating the Cartesian motion and static force, thereby providing information essential to customizing a dual-arm topology suitable for a given task. An example is presented.>