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The optimum selection of a structure for a given application is a capital phase in typological synthesis of parallel robots. To help in this selection, this paper presents a performance evaluation of four translational parallel robots: Delta, 3-UPU, Romdhane-Affi-Fayet, and Tri-pyramid (TP). The problem is set as a multiobjective optimization using genetic algorithm methods, which uses kinematic criteria, that is, global dexterity and compactness, to ensure a prescribed workspace. The results are presented as Pareto fronts, which are used to compare the performances of the aforementioned structures. The obtained results show that the TP robot has the best kinematic performance, whereas the 3-UPU robot is the most compact for a given prescribed workspace.
Serial spherical linkages have been used in the design of a number of robots for minimally invasive surgery, in order to mechanically constrain the surgical instrument with respect to the incision. However, the typical serial spherical mechanism suffers from conflicting design objectives, resulting in an unsuitable compromise between avoiding collision with the patient and producing good kinematic and workspace characteristics. In this paper, we propose a multi-robot system composed of two redundant serial spherical linkages to achieve this purpose. A multi-objective optimization for achieving the aforementioned design goals is presented first for a single redundant robot and then for a multi-robot system. The problem of mounting multiple robots on the operating table as well as the way cooperative actions can be performed is addressed. The sensitivity of each optimal solution (single-robot and multi-robot) to uncertainties in the design parameters is investigated.
This paper introduces the design and the optimization of a probe holder robot for tele-echography applications. To define its kinematic architecture, an approach based on motion capture of an expert's gestures during ultrasound examinations was proposed. The medical gestures analyzed consisted of ultrasound probe movements and were used to characterize the kinematic specifications of the proposed manipulator. The selected architecture was a Spherical Parallel Mechanism (SPM) with 3 degrees of freedom (DoF) and its optimal synthesis was performed using real-coded Genetic Algorithms (GA). The optimization criteria and constraints were established thanks to the collaboration of medical experts and were successively formulated and solved using mono-objective and multi-objective functions.
The objective of this article is to present the dimensional synthesis of serial and
parallel spherical wrists, an important step in the design process of medical robots. This
step is carried out to obtain optimal dimensions of tool-guidance medical robots. With
this goal, we have first studied the specifications of two robots with different medical
applications: one for tele-echography examination and one for minimally invasive surgery.
Then, we have established that the medical needs expressed by the doctors were very
different but the specifications in robotic terms have a lot of common points (kinematics,
workspace, bulkiness). For both applications studied, robots need a mobility of three
rotations around a fixed point (probe contact point on the patient’s skin or trocar
incision). So, a spherical wrist architecture is adapted to their needs. An important
constraint related to medical applications is that the robot must be compact in order to
not obstruct or collide with its environment (medical personnel or patient). We perform
dimensional synthesis allowing determination of dimensions of the mechanism for serial and
parallel spherical wrists, for a tele-echography robot, and a serial wrist for a minimally
invasive surgery robot. We use multi-criteria optimization methods minimizing a cost
function to obtain both good kinematic performance and compactness for the architecture.
The difficulty/challenge of this design process, depending of the studied applications, is
the choice of efficient criteria describing the performances and the constraints of the
robot. The design variables must faithfully represent the specifications of the robot so
that its performance can respond to the medical requirements. We show, here, the different
methods used for optimizing the chosen kinematic architecture for the particular medical
application. These studies lead to prototypes which are validated after medical
experiments. This process of dimensional synthesis will be applied to other medical
applications with different sets of specified constraints.
A general method is presented to automatically determine the placement of manipulators which allows one to optimize multiple kinematic performances indices during the execution of their tasks. It considers the presence of obstacles in the workstation and constraints on the motion of the manipulator's joints. The complete formulation is included, and an example with a six-degree-of-freedom manipulator in a cluttered environment es solved that demonstrates the improvements achieved for the manipulator performances by applying the method.
In order to widen the potentialities of manipulation of the Laboratoire de Mécanique des solides (LMS) mechanical hand, we developed a new planning approach based on the use of a specific exoskeleton. This one has kinematics architecture and dimensions identical to the mechanical hand. This feature allows us to obtain manipulation trajectories for the mechanical hand, very easily and very quickly, by using the exoskeleton, without complex calibration. Manipulation's trajectories are replayed offline with an autonomous control, and, consequently, the exoskeleton is not used with any feedback strategy for telemanipulation. This paper presents the characteristics of this exoskeleton and the graphic interface that we developed. This one uses a method to determine the object's evolution during the manipulation with the exoskeleton, without using exteroceptive sensors. This new approach was tested for standard trajectories by simulation on a Computer-aided design (CAD) robotics system and by using the mechanical hand. Thus, we validate the use concept of an isomorphic exoskeleton to mechanical hand for manipulation planning with the LMS mechanical hand.
This paper addresses the path planning problem for manipulators. The problem of path planning in robotics can be defined as follows: To find a collision free trajectory from an initial configuration to a goal configuration. In this paper a collision-free path planner for manipulators, based on a local constraints method, is proposed. In this approach the task is described by a minimization problem under geometric constraints. The anti-collision constraints are mapped as linear constraints in the configuration space and they are not included in the function to minimize. Also, the task to achieve is defined as a combination of two displacements. The first displacement brings the robot towards to the goal configuration, while the second one allows the robot to avoid the local minima. This formulation solves many of classical problems found in local methods. However, when the robot acts in some heavy cluttered environments, a zig-zaging phenomenon could appear. To solve this situation, a graph based on the local environment of the robot is constructed. On this graph, an A* search is performed, in order to find a dead-lock free position that can be used as a sub-goal in the optimization process. This path-planner has been implemented within SMAR, a CAD-Robotics system developed at our laboratory. Tests in heavy cluttered environments were successfully performed.
This paper proposes an efficient algorithm for computing finger forces involved in a three-dimensional objects grasp. Effective finger force computation is necessary for the successful manipulation on an object by a multifingered robot hand. Based on previous works, the stability forces are computed as a solution of an optimization problem. This optimization problem is mapped into a linear quadratic problem under inequality constraints. We propose a new approach for this problem: the problem is solved as a minimal distance calculation problem in the forces space. The results obtained by simulation demonstrate the efficiency and the numerical stability of the method. This method is used with the LMS mechanical hand as a component of the global control strategy dedicated to the object manipulation.
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.
In this paper, we will present a new 6-DOF parallel robot using a set of
two Delta structures. An effective method is proposed to establish explicit
relationships between the end effector co-ordinates and the active and passive
joint variables. A simulation of the 2-Delta robot on a C.A.D. Robotics system
will also be presented. This simulation will allow us to validate the cohesion
of our calculations, and to show the workspace depending on the mechanical
limits on passive joints variables. Finally, an approach is proposed to study
the influence of small clearances of the passive joint on the precision of the
position and rotation of the effector. This approach is based on a concept
similar to that of Yoshikawa's manipulability.
In this paper we present the SMAR CAD-robotics system (Système de Modélisation et d'Animation de Robots), which we developed at the University of Poitiers. This system allows its user to deal with a great number of robotics problems through the use of a graphic simulator. We will discuss the different parts which form the SMAR system. This includes the following:
—The modeler which allows the user to build a database, describing the robot and its environment. The database generated by the system is composed of the geometric description of the objects and the kinematics description of the environment.
—The simulator and the coordinates reverser, which simulate the robot's movements.
—The collision detection algorithms used to verify task accomplishment.
—A calculation algorithm in order to find optimal placement, which determines the relative position robot/task, allowing the robot to efficiently execute the assigned task.
—The collision free-path planning algorithm allowing the system to generate trajectories in a cluttered environment.
An example dealing with a complex robotized cell will also be presented in order to demonstrate the capabilities of the system.
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