Cyrille Lenders

In vivo three-dimensional kinematics of the cervical spine during maximal axial rotation

The cervical spine exhibits considerable mobility, especially in axial rotation. Axial rotation exerts stress on anatomical structures, such as the vertebral artery which is commonly assessed during clinical examination. The literature is rather sparse concerning the in vivo three-dimensional segmental kinematics of the cervical spine. This study aimed at investigating the three-dimensional kinematics of the cervical spine during maximal passive head rotation with special emphasis on coupled motion. Twenty healthy volunteers participated in this study. Low-dose CT scans were conducted in neutral and in maximum axial rotation positions. Each separated vertebra was segmented semi automatically in these two positions. The finite helical-axis method was used to describe 3D motion between discrete positions. The mean (±SD) maximum magnitude of axial rotation between C0 and C1 was 2.5 ± 1.0° coupled with lateral flexion to the opposite side (5.0 ± 3.0°) and extension (12.0 ± 4.5°). At the C1-C2 level, the mean axial rotation was 37.5 ± 6.0° associated with lateral flexion to the opposite side (2.5 ± 6.0°) and extension (4.0 ± 6.0°). For the lower levels, axial rotation was found to be maximal at C4-C5 level (5.5 ± 1.0°) coupled with lateral flexion to the same side (-4.0 ± 2.5°). Extension was associated at levels C2-C3, C3-C4 and C4-C5, whereas flexion occurred between C5-C6 and C6-C7. Coupled lateral flexion occurred to the opposite side at the upper cervical spine and to the same side at the lower cervical spine.

Three-DOF Microrobotic Platform Based on Capillary Actuation

This paper presents a new microrobotic platform actuated by capillary effects, combining surface tension and pressure effects. The device has 6 degrees of freedom (DOFs), among which, three are actuated: the z-axis translation having a stroke of a few hundreds of microns and θx and θy tilting up to about 15°. The platform is submerged in a liquid and placed on microbubbles whose shapes (e.g., height) are driven by fluidic parameters (pressure and volume). The modeling of this new type of compliant robot is described and compared with experimental measurements. This paper paves the way for an interesting actuation and robotic solution for submerged devices on the microscale.

Assembly of a Micro Ball-Bearing using a Capillary Gripper and a Microcomponent Feeder

Assembly of microsystems is still a challenge today. The numerous parasitic forces often make the manipulation behaviour unpredictable, hence difficult to automate. Therefore special designs of grippers and adequate strategies have to be implemented. Recent works have shown that capillary forces are strong enough to be used to manipulate components in microassembly technology [1]. However, many investigations need to be performed concerning the manufacturing of a microgripper for an industrial use. If the feasibility has been theoretically shown, there is still work to be achieved over the practical implementation of such a gripper.

A gas bubble-based parallel micro manipulator: conceptual design and kinematics model

The parallel mechanism has become an alternative solution when micro manipulators are demanded in the fields of micro manipulation and micro assembly. In this technical note, a three-degree-of-freedom (3-DOF) parallel micro manipulator is presented, which is directly driven by three micro gas bubbles. Since the micro gas bubbles are generated and maintained due to the surface tension between the gas and liquid media, the proposed novel system can be used in the liquid environment which allows for rotation about the X and Y axes and translation along the Z axis. In this technical note, the conceptual design of micro gas bubble-based parallel manipulator is introduced and the input/output characteristic of the actuator is analyzed in detail. The kinematics model of the parallel micro manipulator is also established, based on which the workspace and the system motion resolution are analyzed as a criterion and reference for future prototype development.

Microbubble generation using a syringe pump

The context of this paper is to study the use of capillary microgripper in submerged mediums which requires the use of microbubbles. This paper presents a model and experimentations of the generation of bubbles. In the microsystems which uses liquid, gas bubbles can generate forces due to the surface tension at their interface. To use these bubbles, it is necessary to generate them in a controlled way. In this paper, we propose to study the generation of a bubble having a defined volume, using a syringe pump based device. We first build a mathematical model to predict the growth of the bubble in the liquid. Indeed, the compressibility of the gas and the effect of surface tension are of major importance at microscale, and our model will demonstrate the existence of an instability during the bubble growth. We proceed with a dimensionless study that will allow to predict the existence of the instability on the basis of a dimensionless number. Finally, we present experimental results to validate the mathematical model.

Position Measurement/Tracking Comparison of the Instrumentation in a Droplet-Actuated-Robotic Platform

This paper reports our work on developing a surface tension actuated micro-robotic platform supported by three bubbles (liquid environment) or droplets (gaseous environment). The actuation principle relies on the force developed by surface tension below a millimeter, which benefits from scaling laws, and is used to actuate this new type of compliant robot. By separately controlling the pressure inside each bubble, three degrees of freedom can be actuated. We investigated three sensing solutions to measure the platform attitude in real-time (z-position of each droplet, leading to the knowledge of the z position and Θx and Θy tilts of the platform). The comparison between optical, resistive, and capacitive measurement principles is hereafter reported. The optical technique uses SFH-9201 components. The resistive technique involves measuring the electrical resistance of a path flowing through two droplets and the platform. This innovative technique for sensing table position combines three pairs of resistances, from which the resistance in each drop can be deduced, thus determining the platform position. The third solution is a more usual high frequency (∼200 MHz) capacitive measurement. The resistive method has been proven reliable and is simple to implement. This work opens perspectives toward an interesting sensing solution for micro-robotic platforms.

Surface Tension Effects in Presence of Gas Compliance

In previous chapters, surface tension effects have been extensively detailed. This chapter extends these to take into account gas menisci instead of liquid menisci. Fundamental difference relies in the fact that the meniscus volume is not constant anymore, but now obeys the gas law. This chapter presents how to adapt the models, and discusses also issues about stability of a gas bubble generation. A dimensionless study is presented to predict instability. The experimental validation of the proposed model is also given. Finally, we also present a microrobotic application of this concept.

Parallel microrobot actuated by capillary effects

This paper presents a new actuation mean for a parallel microrobot based on capillary effect, combining surface tension and pressure effects. The device presented is a compliant moving table having 6 degrees of freedom (dof) among which three are actuated: z axis translation having a stroke of a few hundreds of microns, and θx and θy tilt angles up to about 15°. The structure is immersed in a liquid and the actuation principle is based on fluidic parameters (pressure and volume). A model to calculate the stiffness of the system is presented and validated by experimental measurements. Some issues inherent to this type of actuation are also addressed. The presented device is an illustration of a promising solution for microrobotic actuation using capillary effects in a liquid media.

Flexible fluidic actuators: Determining force and position without force or position sensors

Flexible fluidic actuators present a lot of nice features regarding applications in the medical field and in the field of robotics. For example, they own a natural compliance and they can be very lightweight. Besides, an interesting measuring concept seems to be applicable to them: it is possible to determine and control the position of the actuator and the force it develops thanks to the measures of the fluid pressure and of the volume of supplied fluid. This means being able to determine and control the position of the actuator and the force it develops without displacement or force sensors. We validate experimentally this measuring concept in the case of a specific actuator and a method to model the behaviour of flexible fluidic actuators having one degree of freedom is proposed. Besides, the advantages and difficulties brought by this measuring concept are discussed.