196,125 research outputs found
A power recirculating test rig for ball screws: A new perspective for endurance tests
Get PDFBall screw mechanisms are commonly designed and adopted to work for a high number of cycles, so that one of their most relevant characteristics is mechanical endurance. State-of-art experimental setups designed to characterize these mechanisms under operational load conditions require a layout able to withstand high loads and a relevant power to actuate the ball screw, therefore, being rather complex and expensive. To overcome these issues, this paper proposes an innovative test bench exploiting the recirculating power principle, designed for testing a ball screw under operational loads. It enables (at the same time) a reduction of loads on the test rig frame and a reduction of the mechanical power required to actuate the screw. The concept and the design of the proposed test bench are presented, as well as a simplified model to calculate the motor torque and the forces transmitted at the supports. An experimental setup is then realized and tested under actual loads for endurance tests. The results show that the use of the recirculating principle is promising to realize a test rig for endurance tests on a ball screw, thanks to the effectiveness of the solution and the simplicity of the realization of the system even under heavy loads. Among all the measuring instruments adopted (accelerometers, strain gauges, thermocouples and laser sensors for distance measurement on the test bench), the adoption of accelerometers on the nuts seems to be the most promising for condition monitoring, allowing to detect an incipient fault before a macroscopic failure of the ball screw system occurs
Automatic fall monitoring using floor vibration
Get PDFThis work investigates the possibility of monitoring the activity and the falls of people in dwellings using three or more accelerometers fixed on the ground. The main difference between the proposed method and existing ones is the use of acceleration to estimate the impact force by using the apparent mass of the floor; the latter is experimentally identified in each room in which the tests were performed using the heel drop test. The study has two parts: 1. the apparent masses of different dwellings' floors have been measured. 2. the ground reaction force is studied using a purposely designed force platform with a surface of approximately 2 m × 1 m. The force platform allowed the measurement of the forces generated by the falls of 21 subjects, of a crash test dummy (falling in front or rear direction from seated and standing position, with or without the interposition of objects on the trajectory), and of common objects (e.g. dishes, water bottles, books). The impact location is estimated by triangulation, using a wavelet algorithm derived from the existent literature. The results show the possibility of identifying the presence of subjects inside the room and the fall of subjects in the majority of dwellings. We conclude that the proposed method allows a clear distinction between the fall of subjects and objects, given that the difference in terms of force (which is estimated from the floor's apparent mass and from the measured acceleration) is at least of one order of magnitude
Microphone array measurements for the identification of mobile noise sources
No full textA modern parameter in the global quality assessment of high speed trains is the noise emission. An
innovative method for the identification and comparison of mobile acoustic sources was implemented: the
microphone array. Basis of the method is the “beamforming algorithm” that from a measure of the
acoustic pressure in several points allows to investigate the position and the characteristics of the sound
source. This source can be either fixed or moving respect to the array making the method capable of
separating different sources among a general noise signal perceived during a vehicle pass-by.
The method was developed using numerical models and proved to be effective testing it on site with
different known sound sources both fixed and moving.
After these tests an application of the pass-by noise measurements generated by a rail convoy was
investigated. The occasion was given by an experimental campaign settled for the evaluation of noise and
vibration emission of a standard ballast superstructure, within an European research
program(“HIPERTRACK”). Results showed the capability of the method to distinguish multiple sound
sources. The method showed the possibility to identify the noise emitted by a single wheelset. In this
paper an analysis of the noise emitted by the wheel-track interaction of different convoy typologies on the
same ballast superstructure has been performed and results will be discussed. A comparison between
noise and vibration recorded on the rail showed a good agreement. Time/frequency analysis was finally
implemented to identify the spectrum of the emission associated with every single bogie
Falls in older adults: Kinematic analyses with a crash test dummy
No full textFalls have always been a frequent and complex problem that might cause fatality, morbidity, loss or damage of body functions and undesired health care needs. The problem is relevant especially for senior citizens and different studies focused on systems for fall detections. This work analyzes the fall kinematics by means of accelerometers placed on head and torso of a crush test dummy used for fall simulations. This configuration reflects the situation in which the subject does not have any voluntary reaction to possible injuries, which is similar to what occurs during elder people fall. Accelerations were measured upon varying the dummy posture; data obtained from accelerometers were compared with those measured with a vision system. The comparison was based on both the peak velocity and on the fall duration. Results showed the compatibility between the data measured with the two methods, outlining the possibility of identifying the peak velocity from videos available on the internet captured, for instance by video surveillance cameras
A device for pressure measurements on yacht sails
No full textThe present invention relates to the field of ship building, in particular ships propelled by sails, more in particular to sail design.
The present invention discloses a sail pressure measurement system based on MEMS sensors and pressure strips and pads technology. The system is capable to give differential measurement between the leeward and windward side of the sails
Force measurement during gait therapy assisted by a robotic treadmill - The case of Lokomat®
No full textThe present paper deals with force measurement during gait therapy assisted by a special robotic treadmill with driven robotic orthoses that guide inferior limbs movements. The objectives, the measurement setup and the results are presented. This work has been carried out in order to gather data necessary to begin the analysis and the design of a new ankle motion device. The presented results also show how these measurements can be useful in gait parameters assessment and patient's muscle activity level
Dispositivo per prove di rendimento e fatica su viti a ricircolo di sfere
No full textIl dispositivo progettato permette di realizzare prove a fatica sulle trasmissioni meccaniche a viti a ricircolo di sfere e di valutare contestualmente il rendimento meccanico della trasmissione e lo stato di usura della stessa.
Tale dispositivo sfrutta il ricircolo di potenza, ottenuto precaricando, attraverso delle molle a tazza, due chiocciole montate su un unica vite. Tale accorgimento permette di ridurre la potenza meccanica che deve essere introdotta nel dispositivo per realizzare le prove a fatica e nello stesso tempo riduce i carichi che si scaricano sui supporti della vite.
Un opportuno sistema di misura acquisisce il valore della forza di precarico esercitata dalle molle a tazza, le forze scaricate a terra (reazioni vincolari) e la distanza fra le due chiocciole. Attraverso questi dati è possibile valutare il rendimento della trasmissione e il suo stato di usura
Analysis of the failure of a tramcar pantograph component through combined experimental approaches
No full textTramcar vehicles collect the required electrical power from the overhead contact line by means of a pantograph that carries a pan head with collector strips in sliding contact with the contact wire. Therefore, any failure of pantograph or of its components has a direct effect on the correct tramcar operation. The paper deals with a case of unexpected failures occurred on a connection element of the articulated frame of the pantograph of tramcars, causing the interruption of the service. No evidence of impact with the overhead line was detected, only it was clear that the immediate cause was the fatigue failure of a pin of the articulated connection between the upper and the lower arms of the frame of the pantograph. To clarify the original cause of the fatigue failure, an approach combining field measurements, laboratory tests and data processing to obtain the stresses acting on the pantograph failed components under service condition was adopted. It was found that the pantograph was subjected to high level of vibrations coming from the vehicle carbody, mainly due to the track irregularity. A comparative failure analysis was carried out and a solution to upgrade the component subjected to failure was proposed and implemented
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