Definizione, acquisizione sperimentale ed elaborazione di traiettorie di riferimento della mano umana per la sintesi di architetture protesiche di arto superiore

This paper reports an essential part of a wider research activity, which entails the development of a procedure for the Determination of the Optimal Prosthesis Architecture (DOPA) for a given upper limb amputee. A fundamental algorithm of the DOPA procedure performs the kinematic analysis of several prosthetic arm models (also with less than the six degrees of freedom normally required to correctly execute a generic manipulation task). The algorithm must simulate the execution of important daily living activities performed by a prosthesis and thus it requires reference trajectories of the hand. By means of experimental analysis, 59 trajectories of the hand of an able-bodied subject were acquired to identify a modality to correctly perform the corresponding tasks. This paper illustrates in detail the stages of task analysis, experimental acquisition and data processing in order to define the required reference trajectories. The obtained reference trajectories are a temporal succession of the hand pose (position and orientation). A customized algorithm automatically selects the most relevant poses to be considered for the definition of the reference trajectory. The hand pose is reported in the Cartesian Space by means of Natural Coordinates. In order to correctly execute a given task the pose error admitted for the end-effector of the different architectures is associated to each trajectory. In particular, the critical problem to express the orientation error is solved by means of the use of Spherical Rotation Coordinates

Dynamic analysis of a motorbike engine timing system: Experimental and numerical investigation of the geartrain

The development of high-performance vehicle engines requires advanced investigations in order to provide engineers with proper analysis tools to optimize the system design. The elastodynamic behaviour of the engine powertrain may be critical at high velocities (when the flexibility of the system components can have a major role on the overall performance) with consequences on the valve timing and the transmission of dynamic loads. A thorough numerical/experimental investigation was performed on the timing system of a racing motorbike engine. The timing system included the geartrain, which transmits power from the crankshaft to the camshafts, and the valve train, formed by the camshafts and the cam-follower mechanisms for the valve actuation. An experimental campaign was designed and carried out with the purpose of inspecting the timing system behaviour for different velocities and different design parameters. A numerical model was developed in order to provide a simulation/analysis tool that permits the design optimization of the main system components. The present work focuses on the geartrain elastodynamic analysis, which is the main novelty of a long-lasting activity carried out by the authors in collaborations with Ducati Motor Holding S.p.a. (Bologna, Italy). The experimental campaign, the model development and validation, and some simulation results are reported and discussed

A practical procedure for angular resampling applied to motion measurements on a motorbike valvetrain

An experimental test campaign was performed on the valve train of a racing motorbike engine in order to get insight into the dynamic of the system. In particular the valve motion was picked up in cold test conditions by means of a laser vibrometer able to acquire displacement and velocity signals. As usual for rotary machines, the analysis of the experimental data is more significant if performed in the angle domain rather than in the time domain, so that referring the valve time-dependent measurements to the camshaft angular position was required. To this purpose the camshaft was fitted with a zebra tape whose dark and light stripes were tracked by means of an optical probe. Unfortunately, the employed zebra tape presented stripes with slightly different widths, thus precluding the possibility to directly obtain the correct relationship between camshaft angular position and time. In order to overcome this problem, a practical procedure for the zebra tape identification was developed and is the focus of the present paper

Advanced procedures for accelerated vibration-based durability tests

Among vibration qualification tests, durability testing is aimed at verifying components\u2019 endurance against the fatigue damage induced by environmental vibrations. For the sake of practical feasibility, it is often required to accelerate the test duration with respect to the expected lifetime of the component still preserving the entire fatigue damage experienced by the latter during its operational life. The spectral function named Fatigue Damage Spectrum (FDS), which is assumed to estimate the fatigue damage potential of (measured) environmental excitations, is commonly used to synthesize vibratory signals that will then be used as input profiles in the accelerated tests. However, the standard practice presents some limitations: in fact, the synthesized signals are in the form of a Power Spectral Density, thus characterized by a Gaussian signal distribution. This could be a strong limitation given the recurring non-Gaussianity of signals measured in real applications. The statistical parameter known as kurtosis is usually employed to account for the deviation from Gaussianity and a number of kurtosis-control algorithms are proposed in the literature as a solution to make accelerated tests more realistic. Yet, some possible problems associated with these techniques should be highlighted: in particular, the kurtosis is only a global metric that roughly estimates the non-Gaussianity of the input signal neglecting the response of the system, on which \u2013 conversely \u2013 the calculation of the FDS is based. This presentation proposes new methodologies that are based on original algorithms able to synthesize test signals by controlling simultaneously the FDS in conjunction with other target parameters. Each algorithm can control different features of the signal to be synthesized and its selection depends on user demands. The common outcome of these algorithms is the synthesis of non-Gaussian signals, which aim to extend the standard procedures in order to make the accelerated tests more realistic and reliable

Modal Parameter Estimation of a PVC-product Cleaning Machine by means of Operational Modal Analysis

The prototype of a machine tool for the fine machining of PVC window casings was recently developed and tested. Preliminary tests pointed out that excessive vibrations arise during the execution of some operative motion laws, possibly affecting the product quality. Some structural modification of the machine is thus needed in order to reduce the vibration level. In this context, modal analysis of the machine prototype can be useful to guide the design modifications. In order to excite the system consistently with the operative working conditions, the operational modal analysis was considered more suitable than the traditional experimental modal analysis. The excitation was provided by executing of an impulsive motion law of the machine part hosting the tools, which provides a flat spectrum in the bandwidth of interest. This paper illustrates the main practical aspects of the experimental tests and the results that were obtained by using a commercial software

Synthesis of Vibration Signals with Prescribed Power Spectral Density and Kurtosis Value

In the field of vibration qualification testing, random excitations are typically set as input in terms of a PSD profile. The physical motion at the shaker head is obtained through the application of the Inverse Fourier Transform in combination with randomized phases. The overall probability distribution of the input signal tends toward Gaussian, whereas distinctive peaks are often present in real-life random excitations, causing the probability distribution to be non-Gaussian. The parameter known as kurtosis is usually exploited to quantify the feature of non-Gaussianity. Several methods have been proposed to control kurtosis, still maintaining the desired PSD profile, in order to synthesize more realistic signals. However, kurtosis control implemented by some of these methods may be ineffective. In fact, in some cases, the response of a lightly damped system can prove closer to Gaussian than the applied excitation. This work presents two novel algorithms to effectively control kurtosis in random vibration tests are proposed

Experimental Tests of Joint Prototypes for Upper Limb Powered Prostheses

This paper deals with the campaign of experimental tests that has been designed to characterize the prototypes of powered prosthetic articulations developed by the University of Bologna in collaboration with the INAIL Prosthesis Center. In particular the test bench, the test procedures and the software developed to investigate the efficiency and the vibro-acoustic behaviour of the mechanisms are presented

Zebra tape identification for the instantaneous angular speed computation and angular resampling of motorbike valve train measurements

An experimental test campaign was performed on the valve train of a racing motorbike engine in order to get insight into the dynamic of the system. In particular the valve motion was acquired in cold test conditions by means of a laser vibrometer able to acquire displacement and velocity signals. The valve time-dependent measurements needed to be referred to the camshaft angular position in order to analyse the data in the angular domain, as usually done for rotating machines. To this purpose the camshaft was fitted with a zebra tape whose dark and light stripes were tracked by means of an optical probe. Unfortunately, both manufacturing and mounting imperfections of the employed zebra tape, resulting in stripes with slightly different widths, precluded the possibility to directly obtain the correct relationship between camshaft angular position and time. In order to overcome this problem, the identification of the zebra tape was performed by means of the original and practical procedure that is the focus of the present paper. The method consists of three main steps: namely, an ad-hoc test corresponding to special operating conditions, the computation of the instantaneous angular speed, and the final association of the stripes with the corresponding shaft angular position. The results reported in the paper demonstrate the suitability of the simple procedure for the zebra tape identification performed with the final purpose to implement a computed order tracking technique for the data analysis. (C) 2012 Elsevier Ltd. All rights reserved

Synthesis of prosthesis architectures and design of prosthetic devices for upper limb amputees

This chapter presents a procedure for the Determination of the Optimal Prosthesis Architecture for upper limb amputees (DOPA). The presented approach can consistently manage both the clinical aspects and the technical issues involved in the design of electromechanically actuated prostheses. The procedure is composed on one hand of algorithms useful for analyzing the patients\u2019 requirements and on the other hand of algorithms that perform kinematic and kinetostatic simulations of several architectures of artificial arms attempting to fulfil important activities of daily living. The systematic evaluation of the prosthesis models\u2019 performance can methodically guide designers in the synthesis of the optimal prosthesis that best suits the patients\u2019 requirements