Roberto Caracciolo

Frequency dependence of Poisson's ratio using the method of reduced variables

Abstract Measurements of the complex Poissons ratio versus frequency are presented for a common PVC material. Measurements are obtained at several temperatures and then gathered in master-curves for absolute values and phases, by applying the reduced variables method. The curves are flat and this requires special care in applying this method. Reasonable coefficients for the WLF equation have been obtained by applying the causality check before shifting to build up the master curves. Plots of the absolute value at different temperatures overlap well; phase-plots show slopes which do not agree with the general behavior of the master-curve, while mean values of the same plots agree with each other and with the slope of the absolute value. Mismatching of the slopes for the phases is probably due to the plate-effect of the specimen. The causality check, used in determining shifts, compensates for this phenomenon.

Application of causality check and of the reduced variables method for experimental determination of Young's modulus of a viscoelastic material

An accurate determination of the complex dynamic Youngs modulus of a viscoelastic material, in a broad frequency range, is presented in this paper. Curves of Youngs modulus of the tested material (a mixture of polypropylene and calcium carbonate), at different temperatures, are experimentally obtained by means of a laser sensor. The experimental curves are then gathered into a unique master curve, by applying the reduced variables method and a causality check on the curves. The master curve represents Youngs modulus of the viscoelastic material over a much broader frequency range, with respect to the range of a single experimental curve.

A Non-Time Based Controller for Load Swing Damping and Path-Tracking in Robotic Cranes

This paper proposes the use of the non-time based control strategy named Delayed Reference Control (DRC) to the control of industrial robotic cranes. Such a control scheme has been developed to achieve two relevant objectives in the control of autonomous operated cranes: the active damping of undesired load swing, and the accurate tracking of the planned path through space, with the preservation of the coordinated Cartesian motion of the crane. A paramount advantage of the proposed scheme over traditional ones is its ease of implementation on industrial devices: it can be implemented by just adding an outer control loop (incorporating path planning) to standard position controllers. Experimental performance assessment of the proposed control strategy is provided by applying the DRC to the control of the oscillation of a cable-suspended load moved by a parallel robot mimicking a robotic crane. In order to implement the DRC scheme on such an industrial robot it has been just necessary to manage path planning and the DRC algorithm on a separate real-time hardware computing the delay in the execution of the desired trajectory suitable to reduce load swing. Load swing has been detected by processing the images from two off-the-shelf cameras with a dedicated vision system. No customization of the robot industrial controller has been necessary.

The BaBaR drift chamber project

The BaBar Drift Chamber is now under construction. We review its design, the progress in the construction of the components, the plan for assembly and stringing and we present test results obtained with a prototype exposed at SLAC to cosmic rays. We also report on projected dE/dx performance from beam tests done with a chamber with a different cell design.

From CAD Models to Assembly Planning

The use of robots for assembly tasks has not had the expected diffusion. As a matter of fact, assembling robots are today used only in specific environments like for example electronic board assembly or car mass-production. The main reason of this limited use is the robots high cost and the only apparent flexibility. Complete flexibility requires either evolution of the off-line programming systems which is still complex and machine dependent, and the realisation of efficient and reliable task level planning systems, directly related to both design and programming phases.

Deformation Control in Rest-to-Rest Motion of Mechanisms with Flexible Links

This paper develops and validates experimentally a feedback strategy for the reduction of the link deformations in rest-to-rest motion of mechanisms with flexible links, named Delayed Reference Control (DRC). The technique takes advantage of the inertial coupling between rigid-body motion and elastic motion to control the undesired link deformations by shifting in time the position reference through an action reference parameter. The action reference parameter is computed on the fly based on the sensed strains by solving analytically an optimization problem. An outer control loop is closed to compute the references for the position controllers of each actuator, which can be thought of as the inner control loop. The resulting multiloop architecture of the DRC is a relevant advantage over several traditional feedback controllers: DRC can be implemented by just adding an outer control loop to standard position controllers. A validation of the proposed control strategy is provided by applying the DRC to the real-time control of a four-bar linkage.

Design and Calibration of an Opto-mechanical Appliance for 3D Non-contact Orthopedic Measurements Part I: Mathematical Model and Laboratory Prototype

An opto-mechanical system performing fast and accurate non-contact foot measurements is proposed. By processing the measured data it is possible to get three-dimensional foot models and to design custom-made shoes. This work is subdivided into two parts: in Part I, after introducing the system operating method and describing the vision technology employed, a mathematical model of the system is developed accounting for the main internal parameters of the camera. In order to reduce scanning time and the time necessary to create the 3D foot model, the measured data have been arranged in a particular structure and a suitable acquisition procedure has been developed. A laboratory prototype has been built to test the performances of the system: a detailed analysis of its geometry and of its components is provided as well as a concise description of the simple user interface developed to run and control the system.

The automated stringing system for the BaBar drift chamber

Abstract After discussing the motivations for the project, the automated equipment used for the BaBar Drift Chamber stringing is described. Details are given mainly concerning the crucial points of setting-up and calibration. The focus is on the high accuracy reached by a large and complex mechanical tool.

Accurate Modelling of a Controlled Pneumatic Actuator with Experimental Validation

This work presents an accurate model of a controlled pneumatic actuator. The work is concurrent with the development of a new control algorithm for this kind of system, based on an accurate thermo-mechanical model and oriented to perform a complete trajectory control. The actuator is composed of a proportional servovalve and a cylinder with magnetic tracking. The cylinder is supported by a pair of linear bearings. The model proposed for the valve is based on a static experimental characterization. The model of the cylinder is obtained by assuming that the thermodynamic processes in both chambers are isothermal, and that the air is a perfect gas. Numerical simulations are compared with experimental recordings for step and sine input in open chain conditions.

History-Dependent Assembly Planning

An history dependent planner for mechanical assembly is presented. Also non-mating operations are considered. The main feature of the proposed approach is the dynamic generation of the assembly plan. Only the best sequence is found. Selecting criteria are based on mechanical and technological constraints. Three modules are developed to interface the planner with a CAD environment, to determine all possible subassemblies allowing non linear planning and to manage the dynamic expansion of the assembly tree. A planning result is reported.