Modeling of Flexible Bodies for the Study of Control in the Simulink Environment

When studying complex mechatronic systems, it is useful to build models able to simulate both the dynamics of the phenomenon and the control system applied. Typically, the bodies involved are modeled as rigid bodies. In this work, a technique for modeling flexible bodies in Simulink environment is presented. Simulink is a powerful instrument where it is quite easy to integrate control algorithms with complex systems. The solution developed is presented and applied to a machining center. Modern machining centers ensure a level of accuracy that traditional manual machines cannot reach. Simulations of the working process considering vibrations are needed to obtain high precision machining. These simulations aim to determine the error in the position of the tool and to help designers in finding the optimal solution in terms of machining velocity and precision. This work is focused on the carriage of a machine tool moving along horizontal guides, typically named Z-axis. The axis is actuated and borne by a linear motor; therefore, movable constraints must be modeled. A finite-element (FE) model of the carriage was reduced with a Craig-Bampton reduction to provide the mass and stiffness matrices for an in-house Matlab simulation code. The rigid constraints of the carriage were implemented in the model as moving stiffnesses, and their value was set to obtain continuity of the constraints in the discrete model. In the end, a map of different vibrational configurations is proposed to visualize the possible errors that a machining process can generate

Design of a Spherical UGV for Space Exploration

The paper presents the design of a spherical UGV (Unmanned Ground Vehicle) for exploration of critical, unknown or extended areas, such as planetary surfaces. Spherical robots are an emerging class of devices whose shape brings many advantages, e.g. omni-directionality, sealed internal environment and protection from overturning. Many dedicated sensors can be safely placed inside the sphere and the robot can roll in any direction without getting stuck in singular configurations. Specifically, the proposed UGV is thought to collect images and environmental data, so required sensors are firstly discussed to evaluate in sequence of the payload in terms of size and energy consumption. The most effective drive mechanism is selected considering several possible concepts and carrying a trade-off process based on the requirements for a space mission. The optimal solution involves the use of a single pendulum: a hanging mass, attached to the central shaft of the sphere, is shifted to produce rolling. The design issues due to the selected mechanism are discussed, showing the effect of design parameters on the expected performance. For instance, the barycenter offset from the center of the sphere plays a crucial role and affects the maximum step or inclines that can be overcomed. Therefore, the pre-design phase is conducted by discussing the functional design of the robot and introducing a differential mechanism for driving and steering. A quasi omni-directionality is achieved and the mechanical components, opportunely designed according to the loads acting on the device, are arranged to match the mission requirements. Moreover, the mechatronic integration is discussed: microcontrollers, drive electronics, sensors and batteries are sized in order to reach 3 hours of continuous operation. The multibody system is finally modelled in Matlab-Simscape to verify the mechanism for the UGV testing in specific cases. Results show that a suitable layout is a 0.5 m diameter spherical UGV with a steel main structure, mounting 2 DC motors that activate a bevel gear by means of pulleys and timing belts. The spherical shell, with the internal mechanism and electronics, has a total mass of 25 kg and from standstill it can climb up to 15 degrees inclines or steps up to 25 mm, as proved by Matlab simulations. Future works will focus on the realization of the physical prototype, as well as navigation and control strategies

Gait Phases Detection in Elderly using Trunk-MIMU System

The increasing interest towards wearable Magnetic Inertial Measurement Units (MIMUs) for gait analysis is justified by their low invasiveness, confirmed repeatability and complete independence from laboratory constraints. However, some crucial doubts about the identification of a suitable sensor set-up and algorithm in different gait conditions and populations still exist. In this context, the principal aim of the present study was to investigate the effect of different walking conditions on the accuracy of gait phases detection with a trunk-MIMU system. Eleven healthy elderly subjects performed gait trials in four different walking conditions (fast speed, normal speed, slow speed and normal speed with dual-task). A stereophotogrammetric system was adopted as gold standard. The accuracy of the estimation of stance and swing phases was evaluated from the comparison of trunk-MIMU to the stereophotogrammetric system. Mean error values smaller than 0.03 s confirmed the accuracy of the tru nk-MIMU algorithm for an elderly population. Consequently, trunk-MIMU system can be considered suitable for the characterization of gait phases in elderly subjects regardless of walking conditions

Evaluation of the Performances of Two Wearable Systems for Gait Analysis: A Pilot Study

Wearable sensor systems to perform human motion analysis are receiving increasing attention in different application fields. Among wearable sensors, inertial sensors have promising features. However, before they can be employed routinely in clinical applications, it is important to evaluate their reliability. Gait analysis was performed on one male volunteer: data were simultaneously collected with HGait System, based on magnetic and inertial measurement sensor units system, and with STEP32, a commercial electromechanical system already used in clinics. Spatio temporal parameters and joint kinematics in the sagittal plane obtained with H-Gait and STEP32 are compared. The MIMUs system provides a reliable estimation of spatiotemporal parameters, and acceptable hip and knee kinematic curves, while ankle joint measurements must be improved to be clinically useful

Access to credit in times of crisis: measures to support firms and households

The financial crisis that started in August 2007 has led to a worsening in the conditions of credit supply to customers. Since the second half of 2008, several measures have been adopted in order to sustain access to credit for both firms and households, such as debt moratoria, provisions of guarantees on specific types of loans, and various forms of incentives to increase the supply of lending. The initiatives aimed at firms have been sizeable, involving financial resources up to as much as 5 per cent of total bank loans granted between the beginning of 2009 and September 2011. The corresponding value for households has been more modest, slightly above 1 per cent; this is mainly because of the strict qualification requirements applied to some of the initiatives and to their limited financial endowment.access to credit, debt moratoria, guarantee provisions

An ISB-consistent Denavit-Hartenberg model of the human upper limb for joint kinematics optimization: validation on synthetic and robot data during a typical rehabilitation gesture

Several biomedical contexts such as diagnosis, rehabilitation, and ergonomics require an accurate estimate of human upper limbs kinematics. Wearable inertial measurement units (IMU s) represent a suitable solution because of their unobtrusiveness, portability, and low-cost. However, the time-integration of the gyroscope angular velocity leads to an unbounded orientation drift affecting both angular and linear displacements over long observation interval. In this work, a Denavit-Hartenberg model of the upper limb was defined in accordance with the guidelines of the International Society of Biomechanics and exploited to design an optimization kinematics process. This procedure estimated the joint angles by minimizing the difference between the modelled and IMU-driven orientation of upper arm and forearm. In addition, reasonable constraints were added to limit the drift influence on the final joint kinematics accuracy. The validity of the procedure was tested on synthetic and experimental data acquired with a robotic arm over 20 minutes. Average rms errors amounted to 2.8 deg and 1.1 for synthetic and robot data, respectively. Clinical Relevance - The proposed method has the potential to improve robustness and accuracy of multi-joint kinematics estimation in the general contexts of home-based tele-rehabilitation interventions. In this respect adoption of multi-segmental kinematic model along with physiological joint constraints could contribute to address current limitations associated to unsupervised analysis in terms of monitoring and outcome assessment

Wearable Inertial Sensors to Assess Standing Balance: A Systematic Review

Wearable sensors are de facto revolutionizing the assessment of standing balance. The aim of this work is to review the state-of-the-art literature that adopts this new posturographic paradigm, i.e., to analyse human postural sway through inertial sensors directly worn on the subject body. After a systematic search on PubMed and Scopus databases, two raters evaluated the quality of 73 full-text articles, selecting 47 high-quality contributions. A good inter-rater reliability was obtained (Cohen’s kappa = 0.79). This selection of papers was used to summarize the available knowledge on the types of sensors used and their positioning, the data acquisition protocols and the main applications in this field (e.g., “active aging”, biofeedback-based rehabilitation for fall prevention, and the management of Parkinson’s disease and other balance-related pathologies), as well as the most adopted outcome measures. A critical discussion on the validation of wearable systems against gold standards is also presented

Developmental trajectories of physical aggression: prediction of overt and covert antisocial behaviors from self- and mothers’ reports

"Physical aggression declines for the majority of children from preschool to elementary school. Although this desistance generally continues during adolescence and early adulthood, a small group of children maintain a high level of physical aggression over time and develop other serious overt and covert antisocial behaviors. Typically, researchers have examined relations of developmental changes in physical aggression to later violence with teachers’ or mothers’ reports on surveys. Little is known about the degree to which children’s self-reported physical aggression predicts later antisocial behavior. The longitudinal study in this article had a staggered, multiple cohort design. Measures of physical aggression were collected through self- and mother reports from age 11–14 years, which were used to construct trajectory groups (attrition was 6 and 14% from age 11–14, respectively, for self- and mother reports). Overt and covert antisocial behaviors were self-reported at age 18–19 years (attrition was 36% from age 11 to 18–19). Four trajectory groups (low stable, 11%; moderate-low declining, 34%; moderate declining, 39%; high stable, 16%) were identified from self-reports, whereas three trajectories (low declining, 33%; moderate declining, 49%; high stable, 18%) were identified from mothers’ ratings. We examined the prediction of overt and covert antisocial behaviors in early adulthood from the high stable and the moderate declining trajectories. According to both informants, higher probability of belonging to the high stable group was associated with higher overt and covert antisocial behavior, whereas higher probability of belonging to the moderate declining group was associated with higher covert antisocial behavior. Our results support the value of children’s as well as mothers’ reports of children’s aggression for predicting different types of serious antisocial behavior in adulthood." [author's abstract