Med Amine Laribi

Clearance, Manufacturing Errors Effects on the Accuracy of the 3-RCC Spherical Parallel Manipulators

This paper deals with the analysis of a spherical parallel manipulator (3RCC) to determine the error on the pose of the end effector as a function of the manufacturing errors of the different links and the presence of a clearance in the joints. The obtained model allowed us to identify the error on the platform in three cases, i.e., only manufacturing errors were considered, then only clearance in the joints was considered and finally the case of both sources of error were present in the system. It was shown, in particular, that the axial displacement in the C joints is quite important. The second result is the fact that the superposition principle does not work when we consider both the manufacturing errors and the clearance despite the assumption of small displacements.

Redundantly actuated 3-RRR spherical parallel manipulator used as a haptic device: improving dexterity and eliminating singularity

This paper discusses the study of a spherical parallel manipulator (SPM) used as a haptic device for tele-operation applications. The SPM presents poor behavior in singular configurations. Redundancy is used to eliminate the parallel singularity without major changes in the mechanical structure. Comparisons in terms of kinematic and dynamic behavior between the non-redundant and redundant SPM are presented. The results prove the advantage of introducing redundancy in the actuator and sensor to improve the behavior of the SPM. A new control strategy for the redundant SPM is also proposed. The control strategy has been successfully tested and validated on a SimMechanics model.

Optimal synthesis of a spherical parallel mechanism for medical application

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 experts 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.

Development of a spherical parallel manipulator as a haptic device for a tele-operation system: Application to robotic surgery

In tele-operation applications, especially in surgery, haptic devices need to exhibit a high degree of rigidity and accuracy. This paper deals with the development of a spherical parallel manipulator (SPM) that enables the satisfaction of those characteristics. The parallel architecture enables the use of this kind of robot as master in a tele-operation system. Moreover, the SPM has a center of rotation that makes it a natural candidate and more adapted to minimally invasive surgery application. However, the parallel manipulator presents a poor behavior in singular configuration.

Design and optimization of spherical parallel manipulator as a haptic medical device

This paper deals with the design and analysis of a spherical parallel mechanism (SPM) to be used as a haptic device for a medical application. The chosen application is mini invasive surgery during which an anastomosis technique has to be performed. First, the task space, necessary to perform an anastomosis technique, which consists in suturing two parts of a ruptured hollow organ, was determined using a motion capture system. An experimented surgeon was asked to perform the anastomosis technique on a simulator. Several markers were used to track the motion of the hand-tool system during the operation. The experimental data were used to identify the necessary workspace for performing this operation. Then, a spherical parallel manipulator was designed, which has a workspace containing the desired workspace. An optimization procedure was carried out to find the optimal spherical manipulator with the closest workspace to the desired one. Genetic Algorithms were used to solve this problem. The effect of the rotation range around the tool axis on the structure parameters and workspace is also discussed. Finally, the obtained design parameters were shown, through simulation, to yield the required workspace.

An Experimental Analysis of Overcoming Obstacle in Human Walking

In this paper, an experimental analysis of overcoming obstacle in human walking is carried out by means of a motion capture system. In the experiment, the lower body of an adult human is divided into seven segments, and three markers are pasted to each segment with the aim to obtain moving trajectory and to calculate joint variation during walking. Moreover, kinematic data in terms of displacement, velocity and acceleration are acquired as well. In addition, ground reaction forces are measured using force sensors. Based on the experimental results, features of overcoming obstacle in human walking are analyzed. Experimental results show that the reason which leads to smooth walking can be identified as that the human has slight movement in the vertical direction during walking; the reason that human locomotion uses gravity effectively can be identified as that feet rotate around the toe joints during toe-off phase aiming at using gravitational potential energy to provide propulsion for swing phase. Furthermore, both normal walking gait and obstacle overcoming gait are characterized in a form that can provide necessary knowledge and useful databases for the implementation of motion planning and gait planning towards overcoming obstacle for humanoid robots.

A design of slave surgical robot based on motion capture

The synthesis of movement and the biomechanics are introduced into the design methodology for the development of a minimally invasive surgery (MIS) robot manipulator : compact, lightweight and close to the surgical gesture. The goal of this study is progress toward a next-generation surgical robot system that will help surgeons deliver health-care more effectively. Based on an extensive database surgical measurements, the workspace requirements were clearly defined. The pivot point constraint in MIS makes the spherical manipulator a natural candidate. The kinematic model of the proposed structure is performed and singularities are avoided. A synthesis problem is formulated and as a result the optimal link lengths of a medical robot are determined.

Design process for robotic medical tool guidance manipulators

This paper deals with the design process adapted to medical robots. The large diversity of kinematic architectures that can be encountered in medical robotics leads us to seek a robust method dedicated to tool-guidance medical robot design. First, we detail a proposed design process adapted especially for handling the inherent needs in tool-guidance in medical robotics. This proposed method ties together the phases of the design process with their respective tools. We describe the spectrum of medical robots and particularly the variety of kinematic architectures used. Each phase of the design process is detailed through application examples in the domains of tele-echography and minimally invasive surgery, which exhibit a number of commonalities. The use of tools for accomplishing the various steps of the design process is detailed, with emphasis on medical gesture analysis. This is followed by topological and dimensional synthesis. This study illustrates how the type of medical robot can impose specific requirements and a particular approach in the design process. We expect through this paper to bring a significant contribution to the design of medical tool-guidance robots and to facilitate their integration in the clinical environment. The main contribution of this work is to propose a design process method for robotic medical tool-guidance manipulators.

Improvement of the direct kinematic model of a haptic device for medical application in real time using an extra sensor

This paper deals with a spherical parallel manipulator developed for a master device, used in a teleoperation system for surgical application. The aim is to improve the calculation of the direct kinematic model (DKM) even when the parallel manipulator is in a singular configuration by using an extra sensor for a passive joint. A new simple approach for the DKM calculation of the haptic device, in order to meet requirement of real time applications, is developed. The measure of a passive joints angle reduces the calculation time and improves the accuracy of the direct model particularly in the vicinity of the singular positions. Experiments were conducted on tele-operation system despite of the presence of singularities in the master workspace. The obtained results demonstrate the feasibility of the approach.

Optimal torque distribution for a redundant 3-RRR spherical parallel manipulator used as a haptic medical device

Abstract An optimal torque distribution approach for a redundant 3-RRR spherical parallel manipulator (SPM) with haptic capabilities is presented. The redundancy increases the number of solutions for the actuated joint torques for a given SPM configuration and given reference torques. The values of the joint torques are optimized, first, to eliminate the effect of singularity on the SPM and, second, to minimize the torque developed by the actuators. A SimMechanics model is used to validate the proposed approach. Experimental validation is also carried out. The results show the advantage of introducing redundancy of actuators to improve the behavior of the SPM.