Design criteria for grinding machine dynamic stability

Abstract Surface grinding is one of the oldest and most widely used machining process: to date, there are still few alternatives available for producing smooth and flat surfaces, satisfying both technical and economic constraints. The quality of a workpiece resulting from a grinding process is strongly influenced by the static and dynamic behavior of the mechanical system, composed by machine tool, wheel, fixture and workpiece. In particular, the dynamic compliance of the machine at wheel-workpiece interface may cause vibrations leading to poor surface quality. Starting from the analysis of process-machine interaction according to self-excited vibrations theories (the most relevant), this paper outlines a path for surface grinding machines design, focused on the identification of the most critical dynamic eigenmodes both in terms of dynamical parameters and geometry (vibration direction). The methodology is based on the application of Nyquist stability criterion for MIMO systems. Firstly, the methodology distinguishes between a limitation mainly ascribable to regenerative chatter and one ascribable to closed-loop eigenmodes properties. In this latter case, it will be shown that stability properties are strongly influenced by the shape and orientation of the elliptical movement of the wheel entailed by the limiting eigenmode (that, in general, is complex). Such an analysis can be also exploited to provide some indications guiding machine structural modifications. Finally, the approach is demonstrated on a couple of grinding machine variants via FE modeling

Analysis of Vibration Damping in Machine Tools

AbstractThe dynamic behavior of a machine tool structure directly influences key metal cutting performance like being able to quickly remove hard workpiece material during roughing or minimize unwanted oscillations during high speed movements in finishing. While structure conception is still funded on designer experience and inventiveness, Finite Element models are very effective in analyzing the conceived structure, allowing its optimization, in term of stiffness increase and/or mass reduction.While today FE models provide a satisfying description of structure distributed stiffness and inertia, machine damping is usually not represented or is approximated as a uniform viscous damping, with no precise reference to the actual dissipation phenomena occurring in the structure. The corresponding incertitude in the estimation of the overall dynamic behavior often strongly limits the possibility of delivering accurate absolute estimations of machine performance. In order to overcome this limitation, this work aims at adding key energy dissipation mechanisms into numerical structural models: the velocity loop of the axis position controller, the frictional forces acting on the axis kinematic chain and guide ways and a distributed modal damping. Experimental tests have been performed on a machine tool axis equipped with tunable roller plus plain friction guide ways. The proposed model shows how different components and phenomena contribute into increasing machine performance, in term of material removal capacity. Given that the resulting models are essentially non-linear, appropriate methodologies are also suggested to integrate the proposed analysis into the usual machine development design cycle

Body-scaled action in obesity during locomotion: Insights on the nature and extent of body representation disturbances

Objective Conscious perception of our own body, also known as body image, can influence body-scaled actions. Certain conditions such as obesity are frequently accompanied by a negative body image, leaving open the question if body-scaled actions are distorted in these individuals. Methods To shed light on this issue, we asked individuals affected by obesity to process dimensions of their own body in a real action: they walked in a straight-ahead direction, while avoiding collision with obstacles represented by door-like openings that varied in width. Results Participants affected by obesity showed a body rotation behavior similar to that of the healthy weighted, but differences emerged in parameters such as step length and velocity. Conclusion When participants with obesity walk through door-like openings, their body parts rotation is scaled according to their physical body dimensions; however, they might try to minimize risk of collision. Our study is in line with the hypothesis that unconscious body-scaled actions are related to emotional, cognitive and perceptual components of a negative body image

Low-Intensity Whole-Body Vibration: A Useful Adjuvant in Managing Obesity? A Pilot Study

The use of whole-body vibration (WBV) for therapeutic purposes is far from being stan- dardized and an empirical foundation for reporting guidelines for human WBV studies has only very recently been published. Controversies about safety and therapeutic dosage still exist. The present study aimed to investigate the metabolic and mechanical effects of low-intensity WBV according to the ISO 2631 norm on subjects with obesity. Forty-one obese subjects (BMI ≥35 kg/m2) were recruited to participate in a 3-week multidisciplinary inpatient rehabilitation program including fitness training and WBV training. During WBV the posture was monitored with an optoelectronic system with six infrared cameras (Vicon, Vicon Motion System, Oxford, UK). The primary endpoints were: variation in body composition, factors of metabolic syndrome, functional activity (sit-to-stand and 6-min walking test), muscle strength, and quality of life. The secondary endpoints were: mod- ification of irisin, testosterone, growth hormone, IGF1 levels. We observed significant changes in salivary irisin levels, Group 2 (p < 0.01) as compared to the control group, while muscle strength, function, and other metabolic and hormonal factors did not change after a 3-week low-intensity WBV training with respect to the control group. Future studies are needed to further investigate the potential metabolic effect of low-intensity WBV in managing weight

An Integrated Multi-Sensor Approach for the Remote Monitoring of Parkinson’s Disease

The increment of the prevalence of neurological diseases due to the trend in population aging demands for new strategies in disease management. In Parkinson's disease (PD), these strategies should aim at improving diagnosis accuracy and frequency of the clinical follow-up by means of decentralized cost-effective solutions. In this context, a system suitable for the remote monitoring of PD subjects is presented. It consists of the integration of two approaches investigated in our previous works, each one appropriate for the movement analysis of specific parts of the body: low-cost optical devices for the upper limbs and wearable sensors for the lower ones. The system performs the automated assessments of six motor tasks of the unified Parkinson's disease rating scale, and it is equipped with a gesture-based human machine interface designed to facilitate the user interaction and the system management. The usability of the system has been evaluated by means of standard questionnaires, and the accuracy of the automated assessment has been verified experimentally. The results demonstrate that the proposed solution represents a substantial improvement in PD assessment respect to the former two approaches treated separately, and a new example of an accurate, feasible and cost-effective mean for the decentralized management of PD

Computation of spatio-temporal parameters in level walking using a single inertial system in lean and obese adolescents

In recent years, the availability of low-cost equipment capable of recording kinematic data during walking has facilitated the outdoor assessment of gait parameters, thus overcoming the limitations of three-dimensional instrumented gait analysis (3D-GA). The aim of this study is twofold: firstly, to investigate whether a single sensor on the lower trunk could provide valid spatio-temporal parameters in level walking in normal-weight and obese adolescents compared to instrumented gait analysis (GA); secondly, to investigate whether the inertial sensor is capable of capturing the spatio-temporal features of obese adolescent gait. These were assessed in 10 obese and 8 non-obese adolescents using both a single inertial sensor on the lower trunk and an optoelectronic system. The parameters obtained were not statistically different in either normal-weight or obese participants between the two methods. Obese adolescents walked with longer stance and double support phase compared to normal-weight participants. The results showed that the inertial system is a valid means of evaluating spatio-temporal parameters in obese individuals

Dizziness and Falls in Obese Inpatients Undergoing Metabolic Rehabilitation

The relationship between dizziness and falls in the obese population is a relatively unexplored issue. The aims of the present study were to define the 1-year prevalence of dizziness in an obese inpatient population undergoing metabolic rehabilitation and to investigate possible correlations with fall events

Role of imaging in rare COVID-19 vaccine multiorgan complications

As of September 18th, 2021, global casualties due to COVID-19 infections approach 200 million, several COVID-19 vaccines have been authorized to prevent COVID-19 infection and help mitigate the spread of the virus. Despite the vast majority having safely received vaccination against SARS-COV-2, the rare complications following COVID-19 vaccination have often been life-threatening or fatal. The mechanisms underlying (multi) organ complications are associated with COVID-19, either through direct viral damage or from host immune response (i.e., cytokine storm). The purpose of this manuscript is to review the role of imaging in identifying and elucidating multiorgan complications following SARS-COV-2 vaccination—making clear that, in any case, they represent a minute fraction of those in the general population who have been vaccinated. The authors are both staunch supporters of COVID-19 vaccination and vaccinated themselves as well