Houssem Saafi

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.

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.

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.

Tele-operation control system for non-homothetic master/slave kinematics for minimally-invasive surgery

The current objective of this robotics research study is mainly to develop a cheap and not cumbersome systems for special applications. A PROMIS (Pprime RObot for Minimally Invasive Surgery) system is designed with this philosophy. The developed system is composed of master, slave and control system for collaborative operation between the surgeon and the robot. A parallel robot haptic device is used as master to teleoperate a serial robot with three degrees of freedom (dof). The advantage of this method is the possibility of coupling master and slave with non-matching kinematics through a kinematic transformation. The developed control system architecture is presented in this paper. The control architecture was designed to control the teleoperation system where the master and slave robots do not have homothetic kinematics. Finally, the viability of the developed control is demonstrated by the experimental results.

Forward Kinematic Model of a New Spherical Parallel Manipulator Used as a Master Device

The paper discusses the Forward Kinematic Model (FKM) of a special Spherical Parallel Manipulator (SPM). The special SPM is obtained by modifying one leg of a classic SPM. This new architecture eliminates the singularity from the workspace. The SPM is used as master device for medical tele-operation system. The FKM of the new SPM is calculated using the equation of spherical four-bar mechanism. A method to improve the FKM calculation using extra sensor is proposed in this paper.

A Real-Time Serial Approach for Solving the Forward Kinematic Model of Spherical Parallel Manipulators

This paper discusses a serial approach to solve the forward kinematic of a spherical parallel manipulator (SPM). The SPM is used as master device in minimally invasive surgery to control a slave robot. The orientation of the moving platform of the SPM is determined by solving the forward kinematic of one serial leg. The forward model is very simple compared to the classical way of solving the forward model using three sensors placed on the base of the SPM and also it does not suffer from parallel singularities which amplify the classic forward model. The serial way of solving the forward model needs a short calculation time which is suitable for real-time applications.

Optimal haptic control of a redundant 3-RRR Spherical Parallel Manipulator

This paper discusses an optimal torque distribution for a redundant 3-RRR spherical parallel manipulator (SPM). The SPM has parallel singular configurations within its workspace. The singularity leads to an amplification of the actuated joint torques which violates the actuator torque limits. The use of a redundant actuator solves the effect of the singularity. The quadratic sum of the actuated joint torques is minimized in order to obtain an optimal torque distribution. Experiments carried out show the advantage of introducing redundancy of actuators to improve the behavior of the SPM.

Optimal design of a new spherical parallel manipulator

This paper deals with the optimization of a New Spherical Parallel Manipulator (N_SPM). The N_SPM is obtained by changing the kinematic of one leg of a classic spherical parallel manipulator. This change is carried out to reduce the presence of the singularity in the useful area of the workspace. The mobility of the N_SPM is similar to the classic one. First, the less-singular working mode of the N_SPM was identified then an optimization of the dexterity is made to eliminate the singularity from the useful workspace. Finally, the optimal N_SPM is presented.

A new serial approach of the forward kinematic model of spherical parallel manipulators for real-time applications

Parallel architectures are increasingly used as haptic devices to provide low inertia, high stiffness and compactness. Thus, spherical parallel manipulators have been developed to generate the three rotational movements in a sufficient workspace. However, these parallel structures have complex kinematic models and can suffer from critical singularity issues. This paper proposes a serial approach to solve the forward kinematic model of a spherical parallel manipulator, which is used as a haptic device in minimally invasive surgery. The new forward kinematic model is based on the serial positioning of the three sensors on one leg rather than placing the three sensors on the three actuated base joints. The forward kinematic model calculation is thus simplified to be suitable for real-time applications (computing time around 5 µs) without cost increase. Parallel singularity effects are removed using this approach and the accuracy of the forward kinematic model is highly enhanced. Simulations were carried out to show the benefits of this approach. The resulting errors of the forward kinematic model calculation due to measurement noises do not exceed 0.2° along the workspace. Experiments were carried out to demonstrate the control of a surgical robot.