Terenziano Raparelli

Experimental and numerical study of friction in an elastomeric seal for pneumatic cylinders

Abstract The behaviour of an elastomeric seal for a pneumatic cylinder piston is analysed in this work. The aim of the paper is to validate experimentally a numerical approach to evaluate seal performance, in actual working conditions. The friction force between seal and the cylinder bore is evaluated through experimental tests and numerical simulations, using a finite element model. Working conditions are simulated for different piston rod velocity and cylinder supply pressure, both in dry conditions, boundary and fluid lubrication conditions. Simulation is obtained by an iterative process that uses the friction coefficient, experimentally measured, as a function of speed and lubrication conditions. Results obtained from experimental tests and numerical simulation are compared to determine the friction force between seal and cylinder bore.

Identification of Discharge Coefficients of Orifice-Type Restrictors for Aerostatic Bearings and Application Examples

In this chapter is described an experimental study conducted in order to identify the supply hole discharge coefficients of externally pressurized gas bearings. Tests were carried out over specific hole, feed pocket and air gap size ranges on pneumatic pads with two types of air feeding systems: annular orifices (inherent orifices) and simple orifices with feed pocket. Air consumption and pressure distributions were measured as a function of supply pressure and air gap height. Discharge coefficients were approximated by an experimental formula based on the Reynolds number and the feeding system geometry. The validity of the formulation found in the study was verified by comparing the numerically calculated pressure distribution with the experimental distribution measured on different pad types. The numerical pressure distribution was calculated using equations for air flow through the supply holes and the Reynolds equations for the air gap.

Experimental study of pneumatic seal extrusion

An experimental study of pneumatic seal extrusion is presented. Direct visual observations are made. An empirical formula for calculating extrusion based on the geometric characteristics of the sealing system is presented.

Frequency transfer function of an opto-pneumatic detector

An example of an opto-pneumatic detectors (OPD) frequency transfer function is presented for the development of an opto-pneumatic interface. The theoretical model is tested through experiments in the laboratory on a real OPD prototype. In this way many of the models parameters are studied and evaluated, such as the dimensions of the gas chamber, the thickness of the absorbent body, and the load of the OPD. The results obtained are good and show the utility of the studies described here.

A New Technique for Safe Pesticide Spraying in Greenhouses

Protection from parasites is an important factor in agricultural operations, and calls for continual monitoring and prompt action when needed. In many cases, the equipment, pesticides and manpower required for this purpose account for the majority of production expenses. Though the use of chemicals has had a major influence on the development of agriculture in the twentieth century, bringing significant benefits, it has also had many side effects on human health, animals and the environment. The ease with which these substances can be used, their initial low cost and the lack of knowledge on the part of growers has led to an overuse of pesticides, with dangerous consequences. Only in the last few years have agricultural techniques brought about improvements in the pesticides used (Hewitt, 2000). There can be no doubt that advances in this field have provided a more effective range of choices, for growers and the environment in particular. Parasites must thus be combated by producing a climate that is unfavourable for them, as well as by using a forceful, accurate and incisive spray technique. To reduce pesticides by using more effective treatments, recent studies have investigated different spray techniques capable of reducing the pesticide dose with very low waste and outflow (Austerweil & Grinstein, 1997). Efficacy of crop spraying depends on two main factors: coverage density and uniformity, and droplet size. For the first factor, it should be emphasised that droplets should reach leaves without any overlapping. The second factor is important because many studies have shown that coarse droplets reduce spraying treatment efficacy. In fact, smaller droplets penetrate the canopy better and, transported by air, can reach each part of the crop without dispersion. This is especially true in the greenhouse, where wind is not a problem. These considerations have spurred interest in the idea of spraying pesticides in a defined volume, i.e., a confined area (Molto et al, 2001) (Ebert et al, 2003). The first step in designing an innovative pesticide sprayer is to study various spraying techniques.

High speed rotors on gas bearings: design and experimental characterization

Gas bearings are employed in a variety of applications from micro systems to large turbomachinery. As they are free from contaminants if supplied with clean air, gas bearings and pneumatic guide-ways are often used in food processing, textile and pharmaceutical industries. The new research works are focused on expanding the applications of gas bearings, in particular at very high speeds. Dental drills for example operate at speeds of over 500 krpm and it seems that a limit for gas bearings without cooling is 700 krpm [1]. Nevertheless in [2] a spindle with 6 mm diameter that operated at 1.2 million rpm is described.

Development of an active orthosis of inferior limb in light structure

The development of an active orthosis for inferior limb is presented. A procedure for the customization of the device is proposed. It is based on the design of few standardized parts and on two alternative ways to measure the relevant features of the user: the first making use of a instrumented template; the second making use of a 3D scanner. Then the complete manufacturing process for production of the structural carbon fiber components is presented.