Roberto Basso

Experimental characterization of damping force in shock absorbers with constant velocity excitation

SUMMARY For the characterization of shock absorbers, which are intrinsically non-linear, it was considered advisable to use the 3D representation of force vs velocity-displacement domain rather than traditional force vs velocity or force vs displacement. Experimental apparatus was therefore designed and constructed to measure the damping force produced by shock absorbers. Data were processed with software suitable for fitting the experimental data functions of several variables. Experiments showed that 3D representation of restoring force allows the non-linearity of shock-absorber damping to be examined more thoroughly.

A METHOD TO ANALYSE THE DYNAMIC BEHAVIOR OF A MOTORCYCLE FRONT SUSPENSION EQUIPPED WITH SEQUENTIAL DAMPERS.

SUMMARY This work analyses the dynamic behavior of a motorcycle front suspension equipped with passive sequential hydraulic dampers, in some operative situations. The dampers, with non-linear and asymmetric characteristics, may be regulated in six different ways. Using experimental elasticity and damping data as reference parameters, and a simplified two-degrees-of-freedom model, some dynamic simulations were carried out in order to define damping parameters for optimal comfort and safety.

Design of a single-tube shock absorber with a pre-established characteristic diagram

The possibility of predetermining the characteristic diagram of a shock absorber is analysed by means of numerical simulation and evaluating the influence of some structural parameters on damping force. An iterative process is applied to determine the opening of the shim valve built into the piston. Characteristic diagram shows different parts, the slopes of which and the points of their changes are analysed by adjusting some structural features, to establish how to operate for obtaining predetermined shapes. The thickness of the shim valves and the preload on the extension valve have greater influence on damping force than other structural parameters.

Damping Measurement of Bending Vibration in Alpine Skis: An Improvement of Standard ISO 6267

The ISO 6267 standard defines a damping measuring method in terms of the half-time of the vibration of clamped alpine skis that is mainly related to the first vibration mode only. By means of the experimental test done in laboratory, it is shown that this method is not able to completely characterize the damping of the skis that depends on the vibration mode considered. For example in the case a ski sample, damping ratio varies from 0.45%±0.05% of the first mode to 2.1%±0.1% of the fourth one. The experimental test done on ski tracks by means of piezo-accelerometers placed on the skis running at speed of 12.5 m/s showed that the skis vibrate according to a combination of at least the first 4 vibration modes and that the snow better excites frequencies greater than the first one. As the excitation frequencies on the skis during the descent are much higher than the first natural frequency of the ski, it appears not correct to hypothesize that only the damping coefficient relative to the first natural frequency is representative of the ski vibrations. To improve the UNI ISO 6267 standard, a new method based on the Fourier Transform filtering to separate the time history into the vibration components is proposed for the characterization of the ski damping that is variable with its natural modes.

A diagnostic tool for the quality control of gear pumps

This work proposes the use of a diagnostic tool based on the triple application of the Fourier Transform to carry out the quality control of gear pumps. The signal analysed is the discharge pressure acquired with a piezoelectric sensor in contact with the fluid near the discharge hole. An analysis was carried out by comparing the behaviour of a set of pumps having the same nominal characteristics but with various types of defects in the gear teeth, which had been made for the purpose of this experiment. A mathematical model of the diagnostic signal for the defective pumps was also developed. This model makes it possible to interpret the diagnostic signal processed with the triple application of the Fourier Transform and detect the presence and position of defects consisting in small scratches in tooth profiles. The tool makes it possible to obtain an acceptance mask for a set of gear pumps of the same series in which the category and size of a defect can be detected.

Monitoring and diagnostics of stresses in reciprocating machines

Abstract This work presents a study for monitoring stresses in links of reciprocating machines by means of indirect measurements. A model of such a machine is a slider-crank mechanism actuated by an asynchronous electric motor with reduction gear. For this study, an experimental simulation apparatus was constructed, composed of a reciprocating machine, a direct-current tachometer as diagnostic sensor, and the necessary instrumentation for measurement of loads acting on the slider and thus stresses on the connecting rod. The excellent agreement between the theoretical and experimental results shows the validity of the solution for monitoring and diagnostics of reciprocating machines using a simple direct-current tachometer connected to an A/D converter and then to a PC able to execute the fast Fourier transforms of the acquired signals. The proposed method is particularly useful when direct measurements of stresses are difficult or particularly laborious. It also allows continuous monitoring of the machine throughout its life time, with user access or denial to computerized information, as desired.

Digital Imaging Exposure-Time Optimisation of Tripod-Camera Vibrating Systems Based on MTF

The problem of exposure-time optimization in digital images acquired by a tripod-camera vibrating system is examined in this paper and an initial analysis is presented. The different noise sources concerning both the acquisition sensor in the camera and external vibrations were studied and quantified in some specific cases. The digital image quality is then discussed in terms of the MTF function evaluated at 50% level in order to define what the optimum ranges of exposure-times are.Copyright

Mechanical Characterization of Linen Fibers: The Turin Shroud Dating

As the 1988 radiocarbon dating of the Turin Shroud (TS) was debatable also from a statistical point of view, new dating methods have been proposed. This paper presents the result of an improved mechanical dating. A recent cyclic-load machine has been improved to better fix fibers under test by using a special support designed for the purpose. The mechanical behavior of linen fibers of three different ages are measured and compared discussing these results in reference to the complex structure of aged linen fibers; the three samples are a linen fiber from an Egyptian mummy of 27th Century B.C.; a linen fiber coming from the TS, and a recent linen fiber. This machine allowed to confirm the previous results regarding the TS mechanical dating, showing that these results are again compatible with the First Century A.D., the period in which Jesus Christ lived in Palestine. The improved machine also showed that the complex nonlinear behavior of the fibers is also due to the packing of the Secondary Cell Wall of the linen fibers, mostly composed of micro fibrils, that produces a memory-effect. The stiffening of the linen fibers with the loading increasing is a property detected for all the tested fibers that must not be forgotten also in the construction of flax fibers based composites.

Vibration Monitoring for Local Fault Detection in Synchronous Belts

The possibility of diagnosing the presence of a fault in a synchronous belt transmission during its work, without dismantling it, by monitoring the vibrations of the pulley support, was investigated in this work. After a few simulations with a multi-body numerical model, several experimental tests were carried out in an apparatus made up of a test bench, motion sensors, a system of signal acquisition and software for data processing. The behavior of mechanical transmissions with healthy and faulty synchronous belts was compared. The damage was simulated by removing a tooth from the belt. The results show that a localized defect on a synchronous belt modifies the frequency spectrum of the motion signals measured on the pulley support. From the experimental tests performed, the following results were obtained: the direction of vibrations measured on the pulley support must be chosen so as to be parallel to the direction of the taut side of the belt; the presence of a defect can be seen in the frequency spectrum by the change in the amplitude of the peaks at the first harmonics of the run frequency; the best condition to highlight the different behaviour in the power spectra occurs when the transmission is under load.© 2008 ASME

Tissue Mechanical Resistance Measurements and Records in Stereotactic Biopsy Procedures

In previous reports the authors have described a fully motorized, Computer driven, stereotactic apparatus1, 5. In a following step a constant velocity dynamometer was built6, and connected with the aim of recording the thrust exerted by the motor while pushing the stereotactic tool on its way to the target. The Output of the instrument was plotted into a bidimensional diagram (X probe track in millimeters; Y force in Newton).