Jordi Cornella

Fast and Flexible Determination of Force-Closure Independent Regions to Grasp Polygonal Objects

Force-closure independent regions are parts of the object edges such that a grasp with a finger in each region ensures a force-closure grasp. These regions are useful to provide some robustness to the grasp in the presence of uncertainty as well as in grasp planning. Most of the approaches to the computation of these regions for N fingers work on the contact space, implying a N-dimensional problem. This paper presents a new approach to determine independent regions on polygonal objects considering N friction or frictionless contacts. The approach works on the object space, implying that it is always a two-dimensional problem and, since it is not necessary to compute all the force-closure space, it becomes a very fast approach. Besides, the approach is also flexible since constraints on the fingers placement can be easily introduced. Some graphical examples are included in the paper showing the simplicity of the methodology.

Augmented Reality for Minimally Invasive Surgery: Overview and Some Recent Advances

Pablo Lamata1,2, Wajid Ali3, Alicia Cano1, Jordi Cornella3, Jerome Declerck2, Ole J. Elle3, Adinda Freudenthal4, Hugo Furtado5, Denis Kalkofen6, Edvard Naerum3, Eigil Samset3, Patricia Sanchez-Gonzalez1, Francisco M. Sanchez-Margallo7, Dieter Schmalstieg6, Mauro Sette8, Thomas Studeli4, Jos Vander Sloten8 and Enrique J. Gomez1 1Universidad Politecnica de Madrid, Spain 2Siemens, United Kingdom 3University of Oslo, Norway 4Delft University of Technology, Netherlands 5Medical Centre Ljubljana, Slovenia 6 Graz University of Technology, Austria 7Minimally Invasive Surgery Centre Jesus Uson, Spain 8University of Leuven, Belgium

On computing form-closure grasps/fixtures for non-polygonal objects

Form-closure independent regions are parts of the object edges such that a grasp with a finger in each region ensures a form-closure grasp. These regions are useful to provide some robustness to the grasp in the presence of uncertainty as well as in the design of fixtures. The paper presents a new approach to compute independent regions for four frictionless contacts. A sufficient condition is stated and used to obtain combinations of two contact points that allow a form-closure grasp. Then, selecting one of these combinations, a set of four independent regions on the object boundary is determined. An example of the proposed methodology is included in the paper

On 2D 4-finger frictionless optimal grasps

The paper deals with the determination of optimal force-closure grasps for 2D polygonal objects. The problem is analyzed and some intrinsic properties of grasps are determined. The approach is applied to the determination of the position of a fourth finger given the positions of three other fingers. Moreover, the range of solutions that allow the force-closure property as well as the optimal value are analytically determined, checking only four points in the worst case. The algorithm has been implemented and numerical examples are included in the paper.

Contact force estimation for backdrivable robotic manipulators with coupled friction

A hybrid model/learning-based dynamic equation has been developed for robots in order to take advantage of the attractive features of both techniques. The regular dynamic equation is used to model the ideal behavior, while wavelets are used to learn the joint friction. The friction may be coupled, such that it is a function of the velocity of multiple joints. Furthermore, a system identification method has been designed to improve contact force estimation, using manual hand excitation in addition to motor excitation. The hybrid dynamic equation was implemented for the PHANTOM Omni haptic device (SensAble Technologies, MA, USA), and experiments were performed to compare using manual excitation with using motor excitation only. The results showed that manual excitation improved contact force estimation performance, with improvements in the relative RMS values ranging from 21% to 35%.

Wavelet networks for estimation of coupled friction in robotic manipulators

A wavelet network (WN) friction model has been developed for robots where the friction is coupled, such that it is a function of the velocity of multiple joints. Wavelets have the ability to estimate random friction maps without any prior modeling while preserving linearity in the model parameters. The WN friction model was compared against the Coulomb+viscous (CV) model through experiments with the PHANTOM Omni haptic device (SensAble Technologies, MA, USA); however, the theory is valid for any serial-chain robotic manipulator. Ability to estimate applied motor torques was used as the performance metric, quantified using relative RMS values. During training of the WN model it outperformed the CV model in all cases, with an improvement in relative RMS ranging from 0.4 to 7.5 percentage points, illustrating the potential of the WN friction model. However, during testing of the WN model on an independent data set results were mixed, highlighting the challenge of achieving sufficient training.

Improving Cartesian position Accuraca of a telesurgical robot

This paper evaluates and improves the capability of the endoscopic surgical robot AESOP (ComputerMotion Inc., Goleta, CA, USA) to carry out tasks autonomously. First, the Cartesian position accuracy of the robot is measured using an optical tracking system. Since the obtained results are not satisfactory, the tracking system is then used to correct the position of the robot. Two approaches are presented: in the first one, the relation between the tracking and the robot reference frames is determined and is kept constant during the execution of a task, while in the second one, some parameters involved in this relation are updated at each sampled time of the system by means of a Kalman filter. The algorithms have been implemented in the real tracking-robot system and numerical results are reported in this paper, showing that the proposed solutions clearly improve the autonomous performance of the original system.

A New Framework for Planning Three-Finger Grasps of 2D Irregular Objects

This paper presents a new approach to obtain three-finger robust grasps of 2D irregular objects. Given a discrete description of the object boundary, a partial representation of the force-closure space considering the position of two contact points is obtained. The computational cost of this representation is low and it still includes enough information to obtain suitable grasps as well as independent regions on the object boundary, such that a finger in each region ensures a force-closure grasp independently of the exact position of the contact points. The procedure has been implemented and several examples of the proposed methodology are included in the paper