This paper analyses lumped-parameter dynamics of a pair of robot fingers with soft and deformable tips pinching a rigid object under the effect of a gravity force. The dynamics of the system in which area contacts between the finger-tips and the surfaces of the object arise are compared with those of a pair of rigid robot fingers with rigid contacts with an object, with or without effect of the gravity. It is then shown that there exists a sensory feedback from measurement of finger joint angles and the rotational angle of the object to command inputs to joint actuators, and this feedback connection from sensing to action realizes secure grasping of the object in a dynamic sense and regulation of the object posture. It is further shown that there are various types of other feedback connections from sensing to action, which can be used in combination of feedback signals for stable grasping and posture control of the object for realizing sophisticated object manipulation.

In this paper two explicit force control schemes for underwater vehicle-manipulator systems are presented. The schemes take into account several factors such as uncertainty in the model knowledge, presence of hydrodynamic effects, kinematic redundancy of the system, and poor performance of vehicle's actuation system. The possible occurrence of loss of contact due to vehicle's movement during the task is also considered, and the adoption of an adaptive motion control scheme is investigated to take advantage of dynamic compensation. The proposed control schemes have extensively been tested in numerical simulation runs; the results obtained in a case study are reported to illustrate their performance.

Robotic laser welding places extreme demands on the spatial accuracy with which the robot must position the focal point of the laser with respect to the joint to be welded. The required level of accuracy is difficult to achieve in a production environment without the use of end-point sensor based control of the robot. This requires that the end-point sensor frame and welding laser frame be accurately calibrated with respect to each other, as well as with respect to the robot wrist frame. This calibration can be difficult to perform since the sensor and laser frames are virtual in the sense that these are located in space with respect to the physical hardware, and the wrist frame of the robot is often not physically accessible. This paper presents the design of a calibration system with which these frames may be precisely defined with respect to each other.

The paper focuses on the problem of point-to-point trajectory planning for flexible redundant robot manipulators (FRM) in joint space. Compared with irredundant flexible manipulators, a FRM possesses additional possibilities during point-to-point trajectory planning due to its kinematics redundancy. A trajectory planning method to minimize vibration and/or executing time of a point-to-point motion is presented for FRMs based on Genetic Algorithms (GAs). Kinematics redundancy is integrated into the presented method as planning variables. Quadrinomial and quintic polynomial are used to describe the segments that connect the initial, intermediate, and final points in joint space. The trajectory planning of FRM is formulated as a problem of optimization with constraints. A planar FRM with three flexible links is used in simulation. Case studies show that the method is applicable.

In this paper we describe a heuristic potential based technique for solving the problem of path planning based on local information for a free flying robot (FFR) in a 3D static environment. A path which maximizes the sum of three functions: (repulsion from obstacles, attraction towards the goal, and level attraction) is chosen. While the repulsive and goal-attraction potentials depend on how close is the FFR from obstacles and goal, respectively, the level-attraction potential maintains a certain altitude at which the FFR should navigate. Two additional heuristics are proposed to overcome the local minima problem and to improve the efficiency of the search process. Simulation results of the proposed technique are presented.

This paper deals with the path planning of non-holonomic vehicles on an uneven natural terrain. It uses the properties of incompressible viscous fluid fields. The full configuration is considered including position and orientation. Lanes are computed instead of a single path. Bounds on curvature and constraints on initial and final orientations are also addressed. By using the Keymeulen/Decuyper fluid method and adding friction forces in the Stokes' equations, the shortest paths or the minimum energy ones can be found, even on an uneven terrain. In addition, in order to satisfy the kinematics and dynamics constraints of a non-holonomic robot a local variation of the shear constraint is used to control the upper bound of the trajectory curvature. Adding small corridors at the departure and destination also satisfies initial and final orientation requirements.

In this paper we have proposed a numerical procedure for determining and evaluating the workspace of the eclipse robot architecture. The eclipse robot is a novel parallel architecture, which has been conceived and designed at the National Seoul University, Korea. The Eclipse robot design has been characterized in term of workspace characteristics, and optimum design solutions have been investigated as functions of the effect of design parameters on workspace.

Most of the calibration methods proposed for the Stewart platform require complex computation or low noise data for the platform's accuracy to be determined. They are not suitable for practical use in a production environment, where the measurement and calibration method should be simple and robust. Using an external laser measuring device to determine the actual accuracy of a Stewart platform, a practical and simple leg length compensating calibration method, that improves the accuracy of the Stewart platform by a magnitude of around 7, is proposed. The procedures and computation algorithms of the calibration method are shown.

In parallel mechanisms, singular configurations (singularities) have to be avoided during motion. All the singularities should be located in order to avoid them. Hence, relationships involving all the singular platform poses (singularity locus) and the mechanism geometric parameters are useful in the design of parallel mechanisms. This paper presents a new expression of the singularity condition of the most general mechanism (6-6 FPM) of a class of parallel mechanisms usually named fully-parallel mechanisms (FPM). The presented expression uses the mixed products of vectors that are easy to be identified on the mechanism. This approach will permit some singularities to be geometrically found. A procedure, based on this new expression, is provided to transform the singularity condition into a ninth-degree polynomial equation whose unknowns are the platform pose parameters. This singularity polynomial equation is cubic in the platform position parameters and a sixth-degree one in the platform orientation parameters. Finally, how to derive the expression of the singularity condition of a specific FPM from the presented 6-6 FPM singularity condition will be shown along with an example.

This paper presents a dynamic model of a planar parallel manipulator including structural flexibility of several linkages. The equations of motion are formulated using the Lagrangian equations of the first type and Lagrangian multipliers are introduced to represent the geometry of multiple closed loop chains. Then, an active damping approach using a PZT actuator is described to attenuate structural vibration of the linkages. Overall dynamic behavior of the manipulator, induced from structural flexibility of the linkage, is well illustrated through simulations. This analysis will be used to develop a prototype parallel manipulator.

A method is presented that compensates for manipulator end-point errors in order to achieve very high position accuracy. The measured end-point error is decomposed into generalized geometric and elastic error parameters that are used in an analytical model to calibrate the system as a function of its configuration and the task loads, including any payload weight. The method exploits the fundamental mechanics of serial manipulators to yield a non-iterative compensation process that only requires the identification of parameters that are function only of one variable. The resulting method is computationally simple and requires far less measured data than might be expected. The method is applied to a six degrees-of-freedom (DOF) medical robot that positions patients for cancer proton therapy to enable it to achieve very high accuracy. Experimental results show the effectiveness of the method.