Benoît Raucent

Development of a Spherical Induction Motor With Two Degrees of Freedom

This paper reports on the development of a spherical actuator with two actuated degrees of freedom (DOFs). The electromechanical conversion principle is that of an induction motor. The paper first discusses possibilities of adapting the actuator to a spherical rotor actuated with an unlimited angular range along two DOFs. These concepts are then characterized and compared by analytical and numerical modeling, and the final shape of the actuator, composed of a two-layer rotor with teeth surrounded by five inductors, is described. A prototype has been built, and its performance, in terms of characteristic torque-speed and efficiency, has been measured.

Surgical inaccuracy of tumor resection and reconstruction within the pelvis: an experimental study.

Background and purpose Osseous pelvic tumors can be resected and reconstructed using massive bone allografts. Geometric accuracy of the conventional surgical procedure has not yet been documented. The aim of this experimental study was mainly to assess accuracy of tumoral resection with a 10-mm surgical margin, and also to evaluate the geometry of the host-graft reconstruction. Methods An experimental model on plastic pelvises was designed to simulate tumor resection and reconstruction. 4 experienced surgeons were asked to resect 3 different tumors and to reconstruct pelvises. 24 resections and host-graft junctions were available for evaluation. Resection margins were measured. Several methods were created to evaluate geometric properties of the host-graft junction. Results The probability of a surgeon obtaining a 10-mm surgical margin with a 5-mm tolerance above or below, was 52% (95% CI: 37–67). Maximal gap, gap volume, and mean gap between host and graft was 3.3 (SD 1.9) mm, 2.7 (SD 2.1) cm3 and 3.2 (SD 2.1) mm, respectively. Correlation between these 3 reconstruction measures and the degree of contact at the host-graft junction was poor. Interpretation 4 experienced surgeons did not manage to consistently respect a fixed surgical margin under ideal working conditions. The complex 3-dimensional architecture of the pelvis would mainly explain this inaccuracy. Solutions to this might be to increase the surgical margin or to use computer- and robotic-assisted technologies in pelvic tumor resection. Furthermore, our attempt to evaluate geometry of the pelvic reconstruction using simple parameters was not satisfactory. We believe that there is a need to define new standards of evaluation.

ROLLMOBS, a new universal wheel concept

This paper presents a new family of omnidirectional and holonomic vehicles or, in short, omnimobile robots. The robot can perform simultaneously longitudinal, translational and rotational motions, providing full mobility. The concept is based on the original combination of a sphere driven by a classical universal wheel. The sphere in contact with the ground provides the robot high performances (load capacity, maximum surmountable bump height) and smooth motion (no vibrations). The universal wheel tread is not a tyre but consist on several freely rotating rollers that allow free motion of the sphere in the plane orthogonal to the roller axis.

Identification of the barycentric parameters of robot manipulators from external measurements

An original procedure for the estimation of the barycentric parameters of a robot is presented. This procedure requires only the processing of measurements provided by an external experimental set-up. The procedure is based on the property that the relations between the robot motion and its reactions on the bedplate are completely independent of the internal joints forces. A convincing validation experiment on a PUMA 562 is reported.

Minimal dynamic characterization of tree-like multibody systems

The dynamic model of tree-like multibody systems is linear with respect to the parameters of mass distribution for instance when barycentric parameters are used. Thus, assuming that the parameters related to the kinematics are perfectly known, these quantities can be estimated through linear regression techniques. The necessary data are obtained by measuring the joint forces and/or torques and the resulting motion given in terms of positions, velocities and accelerations. An alternative method uses measurements of the reaction forces and torques applied to the bedplate.The linearity of the dynamic and reaction models with respect to the barycentric quantities does not however imply that the latter constitute the minimum set of parameters characterizing the mass distribution of the system. In other words, some barycentric parameters may disappear from the models or may be redundant in the sense that they appear only via linear combinations. In the first case they are not identifiable, while in the second case the linear regression technique leads to estimated values which are correct for the combinations but can be erroneous for the individual parameters.The various options taken to derive the dynamic and reaction models by use of the ROBOTRAN programme are briefly reviewed. Then the rules leading to the minimal parametrization are presented and illustrated by means of a practical example related to a robot calibration problem.

Production and characterization of a hydraulic microactuator

In order to improve the power density of microactuators, recent research focuses on the applicability of fluidic actuation at the microscale. The main encountered difficulties in the development of small fluidic actuators are related to production tolerances and assembly requirements. In addition, these actuators tend to comprise highly three-dimensional parts, which are incompatible with traditional microproduction technologies. This paper presents accurate production and novel assembly techniques for the development of a hydraulic microactuator. Some of the presented techniques are widespread in precision mechanics, but have not yet been introduced in micromechanics. A prototype hydraulic microactuator with a bore of 1 mm and a length of 13 mm has been fabricated and tested. Measurements showed that this actuator is able to generate a force density of more than 0.23 N mm(-2) and a work density of 0.18 mJ mm(-3) at a driving pressure of 550 kPa, which is remarkable considering the small dimensions of the actuator.

Computer-assisted and robot-assisted technologies to improve bone-cutting accuracy when integrated with a freehand process using an oscillating saw

BACKGROUND In orthopaedic surgery, many interventions involve freehand bone cutting with an oscillating saw. Such freehand procedures can produce large cutting errors due to the complex hand-controlled positioning of the surgical tool. This study was performed to investigate the potential improvements in cutting accuracy when computer-assisted and robot-assisted technologies are applied to a freehand bone-cutting process when no jigs are available. METHODS We designed an experiment based on a geometrical model of the cutting process with use of a simulated bone of rectangular geometry. The target planes were defined by three variables: a cut height (t) and two orientation angles (beta and gamma). A series of 156 cuts were performed by six operators employing three technologically different procedures: freehand, navigated freehand, and robot-assisted cutting. After cutting, we measured the error in the height t, the absolute error in the angles beta and gamma, the flatness, and the location of the cut plane with respect to the target plane. RESULTS The location of the cut plane averaged 2.8 mm after use of the navigated freehand process compared with 5.2 mm after use of the freehand process (p < 0.0001). Further improvements were obtained with use of the robot-assisted process, which provided an average location of 1.7 mm (p < 0.0001). CONCLUSIONS Significant improvements in cutting accuracy can be achieved when a navigation system or an industrial robot is integrated into a freehand bone-cutting process when no jigs are available. The procedure for navigated hand-controlled positioning of the oscillating saw appears to be easy to learn and use.

ROLLMOBS, a new drive system for omnimobile robots

Typical mobile robot structures (e.g. wheelchairs or car-like robots) do not have the required mobility for common applications such as displacement in an office, hospital, workshop, etc. New structures based on the “universal wheel” (i.e. a wheel equipped with freely rotating rollers) have been developed to increase mobility. However, these structures have important drawbacks such as spurious vibrations and limited load capacity. This paper presents a new type of omnimobile platform using an original combination of spherical wheel and universal wheel. This structure will improve the robot capabilities, i.e., load capacity and surmountable bumps.

A new philosophy for the design of a product and its assembly line

The main objective of the research presented is to develop a new philosophy for product and assembly line design. Most methodologies usually do not consider the interaction between the two design processes in presence. Moreover, most concurrent engineering approaches do not deal with multi-variant products. A research project was initiated to tackle this problem. The computer tool under development, called CISAL, is applicable to multi-variant products, leading to a unique assembly line for all variants. It is subdivided into three main modules, with possible feedback between them: product analysis, operating modes and assembly techniques, and line layout. We present the framework of this project and the underlying methodology.

Two-degree-of-freedom spherical actuator for Omnimobile ROBOT

This paper deals with the design of a two-degree-of-freedom spherical electrical actuator for mobile robotic applications. It presents the different steps involved in this design, namely the choice of the actuation principle, the modelling of the motor (including the electromechanical) the sizing and the manufacture of a first prototype.