Linkage (mechanical) | EPFL Graph Search

A mechanical linkage is an assembly of systems connected to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for example, and are called joints. A linkage modeled as a network of rigid links and ideal joints is called a kinematic chain. Linkages may be constructed from open chains, closed chains, or a combination of open and closed chains. Each link in a chain is connected by a joint to one or more other links. Thus, a kinematic chain can be modeled as a graph in which the links are paths and the joints are vertices, which is called a linkage graph. The movement of an ideal joint is generally associated with a subgroup of the group of Euclidean displacements. The number of parameters in the subgroup is called the degrees of freedom (DOF) of the joint. Mechanical linkages are usually designed to transform

Two degrees of freedom miniaturized gyroscope based on active magnetic bearings

Thomas Bosgiraud

The introduction of the active blocking system, better known as ABS, into cars revealed the growing need for inertial sensing. Among other data, that permit to apprehend the movements of a vehicle, the measurement of the vehicle angular velocity describes the change rate of the vehicle attitude. This measurement has been called by Foucault in 1852 gyroscopic sensing (from the Greek words σκοπειν = observe and γυρος = rotation). The currently available gyroscopes are either very high precision instruments (hence very costly), used in planes, or cheaper products but with a lack of sensitivity to be used in vehicle navigation. Therefore, a real need for gyroscopes combining low cost and precision exists. This thesis proposes to develop a gyroscope based on miniaturized active magnetic bearings (AMB). The advantage of such a device is that the spun mass will be levitated what frees it from any mechanical link to the base of the instrument what render precise classical mechanical gyroscopes so expensive. This thesis presents two prototypes of AMB based gyroscopes. The first one relies on the ball orbit sensing method which is a new theory proposed in this work. Because of the uncertainties due to the nonlinearities inherent to active magnetic bearings, the position of the levitated mass is adaptively controlled. Measurements performed on the prototype have demonstrated the feasibility of this solution with a ball following either a circular or a vertical orbit. The second designed prototype relies on the Newton's second law of motion. Due to the AMB inherent uncertainties and to the force coupling present in the proposed prototype, it has been chosen to drive the levitated mass with a H∞ controller. Simulations are run to compare three different H∞ controllers with the quality of the angular velocity measurement as criterion. Finally, a feed forward H∞ controller showed the best performances in terms of angular velocity measurements during simulations run on the prototype developed during this thesis.

EPFL2008

Soft Cell Simulator: A tool to study Soft Multi-Cellular Robots

Dario Floreano, Jürg Markus Germann, Andrea Maesani, Manuel Stöckli

Modular or multi-cellular robots hold the promise to adapt their morphology to task and environment. However, research in modular robotics has traditionally been limited to mechanically non-adaptive systems due to hard building blocks and rigid connection mechanisms. To improve adaptation and global flexibility, we suggest the use of modules made of soft materials. Thanks to recent advances in fabrication techniques the development of soft robots without spatial or material constraints is now possible. In order to exploit this vast design space, computer simulations are a time and cost-efficient tool. However, there is currently no framework available that allows studying the dynamics of soft multi-cellular systems. In this work, we present our simulation framework named Soft Cell Simulator (SCS) that enables to study both mechanical design parameters as well as control problems of soft multi-cellular systems in an time-efficient yet globally accurate manner. Its main features are: (i) high simulation speed to test systems with a large number of cells (real-time up to 100 cells), (ii) large non-linear deformations without module self-penetration, (iii) tunability of module softness (0-500 N/m), (iv) physics-based module connectivity, (v) variability of module shape using internal actuators. We present results that validate the plausibility of the simulated soft cells, the scalability as well as the usability of the simulator. We suggest that this simulator helps to master and leverage the potential of the vast design space to generate novel soft multi-cellular robots.

2013

Two degrees of freedom miniaturized gyroscope based on active magnetic bearings

Thomas Bosgiraud

EPFL2008