Moustapha Hafez

Laser-Induced Thermocapillary Convection for Mesoscale Manipulation

Modulation of surface stresses is a recent and promising method to perform mesoscale manipulation of components in liquid medium. We present a promising approach using infra red laser-induced thermocapillary-driven flow for handling multiple or single large and heavy objects. The objects are immersed in thin liquid layers and in contact with the substrate surface. These objects can be handled with high speed thermocapillary convection flow reaching significant forces depending on the object sizes. Velocity measurements showed that 92 µm-sized spherical beads can be dragged with velocities of about 5.5 mm/s. Parallel non-contact micromanipulation can be achieved.

Tactile objects based on an amplitude disturbed diffraction pattern method

Tactile sensing is becoming widely used in human-computer interfaces. Recent advances in acoustic approaches demonstrated the possibilities to transform ordinary solid objects into interactive interfaces. This letter proposes a static finger contact localization process using an amplitude disturbed diffraction pattern method. The localization method is based on the following physical phenomenon: a finger contact modifies the energy distribution of acoustic wave in a solid; these variations depend on the wave frequency and the contact position. The presented method first consists of exciting the object with an acoustic signal with plural frequency components. In a second step, a measured acoustic signal is compared with prerecorded values to deduce the contact position. This position is then used for human-machine interaction (e.g., finger tracking on computer screen). The selection of excitation signals is discussed and a frequency choice criterion based on contrast value is proposed. Tests on a sandwich plate (liquid crystal display screen) prove the simplicity and easiness to apply the process in various solids.

Contactless automated manipulation of mesoscale objects using opto-fluidic actuation and visual servoing.

This work describes an automated opto-fluidic system for parallel non-contact manipulation of microcomponents. The strong dynamics of laser-driven thermocapillary flows were used to drag microcomponents at high speeds. High-speed flows allowed to manipulate micro-objects in a parallel manner only using a single laser and a mirror scanner. An automated process was implemented using visual servoing with a high-speed camera in order to achieve accurately parallel manipulation. Automated manipulation of two glass beads of 30 up to 300 μm in diameter moving in parallel at speeds in the range of mm/s was demonstrated.

3D tactile rendering based on bi (multi) stable SMA monolithic systems

Tactile interfaces are deformable surfaces that communicate information through the sense of touch. We propose a new concept for a tactile interface based on monolithic SMA actuators with integrated bi or multi stable structures. This concept allows the development of a new generation of tactile matrices with a high density of SMA micro actuators with high efficiency and low power dissipation. This paper addresses the design of a monolithic SMA micro actuator composed of two flat springs in an antagonistic configuration. Design considerations and first experimental results are presented. The heat transfer is minimized between the springs to avoid coupling effects which would lead to an efficient two-way actuator. The optimization design of the actuator which is covered in this work satisfies both thermal and mechanical specifications.

Thin shell tactile sensing by acoustic wave diffraction patterns

Most of the humanoid robots are covered with curved thin shells. To have a sensitive shell on the robot, normally we need to add an extra layer of electrodes or sensors. In this paper, we realized a tactile shell based on a Lamb wave diffraction method. Surface-contact sensing is calibrated and tested with a finger; the spatial resolution is 17 × 13 on a 100 mm × 75 mm projected-dimension surface. Structure of the tactile shell comprises only four small (25 mm2 × 0.5 mm) piezoelectric ceramics transducers bonded to the edges of the shell. The sensing results have good accuracy with response time less than 15 ms, the presented method is able to be used for a humanoid robots whole-body tactile sensing.

Automated vision-based system for parallel contactless micromanipulation

This paper presents the automated parallel noncontact manipulation of glass beads ranging from 30 up to 300 μm in size under water. Non-contact micromanipulation is performed by generating controllable laser-induced thermocapillary flows that are capable of dragging the beads. Automated manipulation process is achieved with visual servoing in order to accurately manipulate the beads in a parallel and high-speed manner. Image correlation allowed to detect the bead positions and to provide these positions to a mirror scanner that addressed the IR laser beam at a certain position from the bead. By scanning the laser beam from one bead to another, automated parallel manipulation of beads at speeds in the range of mm·s-1 was demonstrated.

A novel laser-based tracking approach for wide field of view for robotics applications

This paper presents the working principle of a laser-based tracker for wide field of view applications. The objective is to develop a motion capture laser tracker based on a cost effective process that operates in the range of sub-centimeter accuracy. The laser tracker has a wide range of motion and can operate at high speed for both indoor and outdoor without the need for light calibration. Traditional laser scanning devices use expensive high dynamic steering mirror mechanism such as galvanometric scanners. The novel approach presented in this paper consists of splitting the tracking action into two sub-systems. First, a static local scanning based on several laser sources is implemented. The second sub-system consists of a global tracking that moves the overall head tracker using two electrical DC servo-motors. Applications targeted are object tracking and inspection of tanks. The approach is also valid for applications where traditional vision systems are not indicated because of non cooperative lighting condition and where an hemispheric field of view is required.

Mesoscale-object handling by temperature modulation of surface stresses

In this work, we present the non-contact manipulation of mesoscale random-shaped, large and heavy objects immersed in thin liquid water (< 0.8 mm). The manipulation principle used is the modulation of surface tension by infra red (IR) laser (1480 nm) absorption. Laser absorption generates surface-tension-driven flows. At the water-air interface, the flows go away from the laser beam (colder region), and at the bottom they go toward the laser (recirculation cell). We use these flows to drag immersed objects toward the laser focus. With laser scanning, several kinds of fluidic patterns can be obtained for specific handlings such as trapping, mixing and sorting of microcomponents. High speed flows can be reached; therefore high velocity particle manipulation can be achieved (several mm/s). Experimental measurements reported a velocity of about 5 mm/s for a spherical glass bead of 90 ¿m in diameter. With these flows, nN range forces are obtained. These forces are about 1000 times larger than forces generated with optical tweezers.