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The paper presents the study of a hub+bearing system for tire pressure monitoring and control. The tire pressure control is of importance to improve vehicle safety and dynamic behavior, and to reduce fuel consumption and emissions. This feature becomes fundamental in the development of fully automated self-driving cars, which recently some important Companies started to study and test. Firstly, a commercial version of such a system was studied experimentally to evaluate the air-flow vs. pressure curves. Then, a 2D numerical model of the system, by using the commercial CFD software Fluent, was developed and a good match was found between the numerical and the experimental results. Subsequently, taking into account the most important geometric parameters that could influence the conductance and also considering the constraints connected to the bearing dimensions, different configurations of the hub+bearing system were studied numerically. Finally, to validate the CFD results different modular hub+bearing systems were built and experimentally tested. In this way, the critical zones in terms of pressure or velocity were detected and guidelines for designing a new system were obtained.

In this paper a prototype of an automatic machine for the herbaceous grafting of tomatoes is presented. The herbaceous grafting is important in order to reduce the use of pesticides. For this reason, its advantages are both on the environment and on the crops quality. This innovative robotic system, electro-pneumatically controlled, was developed by the Department of Mechanical and Aerospace Engineering (DIMEAS) of the Politecnico di Torino in collaboration with the Department of Agricultural Forest and Food Sciences (DISAFA) of the Universita degli Studi di Torino. The aim of this device is to implement a fully automatic machine capable of picking, choosing, cutting and joining the two plants involved in order to obtain the grafted one.

This paper presents some prototypes of textile pneumatic muscles developed at the Department of Mechanical and Aerospace Engineering (DIMEAS) of the Politecnico di Torino. As an application, they are intended to be included in an ‘active suit’ useful for upper limb rehabilitation. They were realized with textile and soft materials in order to guarantee suitable wearability, confort, low weight, small dimensions as required to actuators used in active suits. This paper illustrated the experimental tests carried on these pneumatic muscles prototypes, a theoretical model from literature here applied to these muscles in order to calculate their stiffness, a preliminary active suit prototype for upper limbs rehabilitation purpose. The results obtained, both in terms of contraction and force developed with these prototypes, are highly satisfactory and the preliminary prototype of active suit realized for upper limbs works properly.

The paper describes the design and optimization of an elastomeric piston seal for low-friction, pneumatic cylinders. The performance of the proposed initial geometry was first evaluated by FE, analysis and experimental tests, showing good manufacturing tolerance independence, low friction, force but low wear resistance by comparison with a commercial lip seal. The seal was then re-designed, and optimized by changing its shape at the sliding-contact area to improve the lubrication mechanism. This optimization process resulted in several different configurations with surface texturing and new, cross-sections to generate reservoirs of lubricant close to the contact zone. Accelerated life tests on, seal prototypes were carried out. The best configuration was found to be a multi-lobed annular seal.

A methodology to design an air-lubricated piston seal for pneumatic actuators is described. Such a seal permits a small air leakage through a very narrow gap between the seal lip and the counterpart; this air film both avoids contact and ensures lubrication at the seal-counterpart interface thus permitting reduced friction and wear. Subsequently the use of grease could be limited or avoided. A seal geometry equipped with a self-pressurized balancing chamber was designed to make leakage as insensitive as possible to the supply pressure and to the barrel machining tolerances. A prototype was manufactured and tests were carried out.

The study of innovative textile muscles is useful for the construction of prototypes of active suits. These suits are obtained by inserting small pneumatic muscles into a vest. The muscles allow some movements of the upper limb to be made for rehabilitation or motor recuperation purposes. An innovative textile bellows muscle is presented in this paper, where its performances have been evaluated by means of both an analytic and a numerical model.

The paper presents kinematic and dynamic investigations of the main press forming mechanism of a thermoforming machine. A multibody analysis of this press forming mechanism, which lifts and rotates a press bed, was carried out. Press bed lifting, which is necessary to form the component, is performed by means of a first rod and toggle mechanism. Press bed rotation to eject the formed component is produced by means of a second rod and must be appropriately shifted. These rods are oscillating followers driven by cams, making it possible to precisely define trajectories as a function of the motor shaft rotation angle. Analysis is performed by numerically solving the equations of motion. Cam synthesis on the basis of the oscillating followers’ trajectories makes it possible to obtain cam profiles in order to evaluate pressure angles and check that there is no undercutting. System dynamics is investigated in order to evaluate motor torque and analyse internal stresses on the hinges. In addition, some experimental results and those obtained with the dynamic model are compared. Performance improvement of the actual machine is carried out by modifying the trajectory of the press bed by means of a numerical code at the purpose developed. This approach is more convenient than the use of a commercial multibody code, which is not specifically built for parametric studies.

Several analytical models exist in the literature for predicting the behavior of braided pneumatic muscles (McKibben muscles). Such models take into consideration the various variables and parameters that are related to the muscle geometry, material properties, and the loads applied to the system, and propose various relationships between these variables. Owing to the complexity of the muscle structure, in several cases, instead of a physical model, empirical or experimental models are used, which generally have limited validity for specific muscle types, i.e., they are only valid for a restricted range of operating parameters. This study proposes a new analytical formula based on the geometry of a pneumatic muscle studied in the rest and work phases and a simple experimental method to obtain corrective factors useful to design muscles. A mathematical formula can thus be obtained that allows one to deduce the measurements of interest in the system as a function of the specific parameters and permits one to interpret in qualitative terms the behavior of the muscle at each moment for various values of pressure, contraction, and applied load and to identify any critical situations. This model can therefore be a very useful design tool because it allows one to adapt the muscle geometry based on the required forces and contractions for different applications that are compatible with the muscle structure on which the model is based. This paper also presents a method for evaluating the efficiency of the muscles, useful to better use them in different applications.

This paper presents an analytical model and its experimental validation for assessing friction forces in reciprocating seals for single and double rod pneumatic cylinders. The contributions of individual piston and rod seals are analyzed using a combination of analytical and experimental approaches. The former entails a friction force formulation based on a lumped parameter seal model, whereas the latter involves carrying out measurements on complete actuators. Selecting appropriate test conditions made it possible to analyze separately the contributions that individual seals make to the overall friction measured on complete actuators. Analysis results were validated by means of friction measurements on the actuators seals, which were tested individually in specific devices. The experimental results were interpreted on the basis of the proposed analytical formulation and confirmed its validity.

This paper aims to present a first part of research carried out on pneumatic muscles. The first applications of these actuators were in the innovative research areas as: rehabilitation medical equipments, prosthesis, robotics and exoskeletons. Despite of a large number of applications, theoretical and experimental research in this area are not many, due to there complex structure in which are used new materials, a combination synthetic rubber membrane and polymers fibers. In this article will be presented the experimental results of a specific pneumatic muscle based on which it will be realized a mathematical model to describe its behavior and to determine the parameters that influence largely static and dynamic feature.

This article describes the design of a new test rig for measuring the friction force in pneumatic components and seals. The test rig was designed in order to measure both the overall friction force in a pneumatic cylinder or a valve as a whole, and the single contribution to friction force caused by the sliding seals. To this end, special fixtures and devices were designed and manufactured in order to measure the friction force in piston seals, rod seals and cartridge valve seals individually. Results of friction measurements carried out on pneumatic cylinders with similar characteristics but produced by different manufacturers are presented and compared. A test procedure and a methodology, in order to separate the contributions of the individual seals from the overall friction of the cylinders, is presented.

Functional magnetic resonance imaging analysis has made major strides in recent years, both because of the development of new scanners and owing to magnetic resonance compatible systems that make it possible to stimulate parts of the human body during analysis. The significant gains in our knowledge of the brain that can thus be achieved justify efforts to construct machines with control circuits suitable for this purpose. This paper presents a magnetic resonance compatible mechatronic device with electropneumatic control that can be used to move one or both feet during functional magnetic resonance imaging analysis of the cerebral motor zones. The system is innovative and original. The results obtained at the end of the investigation were good, and demonstrated that the design is feasible.

Analisi e sperimentazione di una metadologia di prova per polimeri riforzati in vetro utili per componenti pneumatici utilizzati in eletrodomestici

This article presents a seal development approach that takes actual operating conditions (mounting, sealed pressure, lubricating conditions), seal material, and counterpart machining tolerances into account. The approach was applied to the design of seals for a commercial pneumatic spool valve. A single seal geometry and two seat configurations were specified on the basis of finite element analysis and experimental tests. The goal was to develop a compact low-friction seal capable of operating dry in order to avoid the use of grease. The investigation focused on seals that are somewhat shorter (i.e., with a smaller radial height to permit application on new valve models) than existing commercial units but whose performance is not inferior. Prototypes of the new seal were manufactured and tested, and a specific device for measuring seal friction force and sealing was developed. The existing commercial seal was also investigated. The commercial seal and the proposed new designs were then compared.

The demand of air bearings is increasing for those applications that require precision linear movements or high-speed rotations. In particular in this paper air pads for air motion technology are studied. The paper analyses the effect of a circumferential groove machined on the pad surface on pressure distribution, air flow consumption and stiffness. Two geometries are investigated and compared: one with three supply orifices and the other with a circumferential groove as well. The static characteristics of the pads are experimentally determined with also the pressure distributions under the pads along the radial and circumferential directions. The experimental pressure distributions are compared with the simulated ones, obtained with a numerical program at the purpose developed. The numerical model considers a general formulation of the supply holes discharge coefficient that can be used also in presence of a circumferential groove.

Externally pressurized grooved gas thrust bearings for shaft systems were studied both numerically and experimentally. Three thrust bearings composed of a symmetric pair of rings facing a shaft collar were tested. The rings, with inner and outer diameters of 52 and 110 mm, respectively, are equipped with a polar array of eight holes, with a 0.35-mm diameter, distributed on a 65-mm-diameter circumference. The influence of a circumferential groove situated in correspondence with the supply holes is discussed. In particular, two thrust bearings have a rectangular cross-sectional groove of 0.7-mm width and 10- and 20-μm depth. A numerical model based on Reynolds' equation is used to study thrust-bearing performance in relation to geometry (diameter of supply holes, clearance, and groove dimensions). A test rig is used to monitor thrust-bearing axial load capacity and stiffness, and evaluate damping and stability at different supply pressure rates. Experimental and numerical results are compared and discussed.

A new technique to spray pesticides is here presented. Fine droplets are sprayed into a defined volume for operator and for enviroment safe. The new spraying technique was investigated both experimentally and numerically. The results obatined are good and verified in an Italian greenhouse.

Spiral yarn composed with an elastomeric filament DOW XLA, from Dow Chemical, and wool fibres outwardly wound around the elastic core presents a complex behaviour when wound on bobbins to be dyed. This article presents a basic mathematical model with the aim of evaluating radial pressure and transversal stress on bobbins at different angles of winding, different yarn tensions and yarn cross-section areas. Considering the additional complexities of the real problem, an experimental comparison of bobbin alterations under different conditions was carried out with the realisation of two experimental sets. The first experimental test bench allows the variation of winding tension, angle of winding and stroke, then experimental tests were carried out on a winding machine SAVIO varying the yarn tension value and adding a mechanical constrain to the device with the aim of reducing yarn-sliding phenomena, in particular during the thermal cycle. The fundamental parameters have been determined as the angle of wind an...

This article describes the development of an innovative method for raising the surface of high-quality fabrics. The method consists of replacing the natural teasels, currently used, with experimental metal teeth, which do not damage the fabric and reproduce the same effect as natural cards. Literature on the subject contains several examples of artificial metal teeth, which have the advantage of a longer life than the natural ones, however, some can mark the fabric along the warp, if not properly sized. The study in question was based on both experiment and theory, by simulating a flexural load on the barb wire and evaluating its rigidity. Excellent results have been obtained from various tests, and have led to the construction of a new industrial fabric-raising machine.

Work on innovative interfaces has led to the development of optopneumatic systems, which can receive an optical control signal and produce a pneumatic output signal. Specifically, the interface discussed here employs what is known as the “photothermic effect” to convert light power into a pneumatic signal. This is crucial in developing actuators that are suitable for use in areas involving explosion hazards or electromagnetic interference problems, where electrical devices are not recommended or must be avoided. In this case, the system converts an optical signal into a pneumatic signal thanks to a light absorption body interposed between the optical source and the operating gas. The investigation was carried out using both theoretical and experimental methods. Essentially, its goals were to compare the behavior of light absorption bodies in a photothermic cell, using different materials that ensure a durable, repeatable coating with little sensitivity to disturbance, and to determine the influence of varying the photothermic cell’s geometric dimensions.

The design of a bistable electro-pneumatic interface based on laminar-to-turbulent jet transition is herein presented. This principle, used in the past to produce air stream controlled fluidic turbulence amplifiers, is now applied to a new interface driven by acoustic waves and controlled through very low power electrical signals. The study was performed experimentally, attempting to find the optimum interface geometry and analysing its sensitivity to acoustic signals in a frequency range from 2 to 20 kHz and at different excitation levels. A piezo-electric buzzer was used as sound source, resulting in a device with electric power consumption of less than 5 mW, able to switch common low/high pressure pneumatic valves.

In high-speed machining there are a number of applications in which the spindle is supported by air bearings. This type of bearings has very low friction and wear, resulting in virtually unlimited life. If the system is designed correctly the radial stiffness on the tool is comparable to that of ceramic ball bearings.

In porous resistances, Darcy’s law provides a good approximation of mass flow rate when the differences between upstream and downstream pressures are sufficiently small. In this range, the mass flow rates are proportional to the porous resistance’s permeability. For gas bearings, the pressure difference is normally higher, and it is known experimentally that the mass flow rates are lower than would result from Darcy’s law. Forchheimer’s law adds an inertial term to Darcy’s law and, when an appropriate coefficient is selected for this term, provides a good approximation of flow rates for the same applications even with the highest pressure differences. This paper presents an experimental and theoretical investigation of porous resistances used in gas bearing and thrust pad supply systems. The porous resistances considered in the investigation were made by sintering bronze powders with different grain sizes to produce cylindrical inserts that can be installed in bearing supply devices. The paper describes the test setup and experimental results obtained for: (i) mass flow rate through single porous resistances at different upstream and downstream pressures and (ii) mass flow rate and pressure distribution on a pneumatic pad featuring the same porous resistances. The theoretical permeability of the chosen porous resistances was calculated, and the results from setup (i) were then used to obtain experimental permeability and to determine the inertial coefficients. The results, which are expressed as a function of the Reynolds number, confirmed the validity of using Forchheimer’s law. The mass flow rates from setup (ii) were compared to those from setup (i) at the same pressure differentials across the resistance.

A numerical analysis on the feeding system of externally pressurised gas bearings, for the correction of the theoretical mass flow rate formula by means of a discharge coefficient, is presented. A flat aerostatic pad with a simple orifice-type feeding system was chosen as case on study, the authors having previously carried out experimental tests on such a prototype. Using the commercial CFD code ANSYS Fluent®, preliminary simulations were carried out on a pad’s geometry using three different flow models. Having selected the flow model able to give the best prediction of the pad’s behaviour in terms of pressure distribution along the air film, additional simulations were carried out on pads with two different diameters of the supply hole, varying the film thickness in a range from 9 to 14 μm. A comparison between numerical and experimental results is presented. In addition, the effect of the flow intake used to perform experimental tests and of the shape of the orifice’s external edge on pressure distribution is analysed.

This article presents a theoretical and experimental analysis of sealless pistons featuring a special geometry capable of eliminating friction in pneumatic cylinders and valves. Three different piston geometries were investigated: tapered, stepped, and slot-pocket. Performance was evaluated for each geometry in terms of pressure distribution, leakage flow rate, and the self-centering force on the piston. The piston configuration that provides the best tradeoff between self-centering thrust and leakage flow rate in the air gap was also determined. The theoretical and experimental results obtained with the different piston designs were then compared.

Static and dynamic characteristics of externally pressurized gas journal bearings with four supply orifices positioned at the central cross section for rotating shaft displacements near the bearing center are investigated. Results for transfer functions and for gas-film coefficients derived using the developed mathematical model are compared with the results derived from numerical computations of a nonlinear distributed parameter model of the gas bearings. Averaging and corrective coefficients are elaborated. The results obtained demonstrate that analytical data are in good agreement with the numerical data for the wide range of parameters and the mathematical model developed makes the simple calculation of static and dynamic characteristics of this type of externally pressurized gas bearings possible. Derived analytical relations for transfer functions and for gas-film coefficients of gas bearings provide an efficient means for designing rotor-bearing systems.

Although the performance and reliability of pneumatic cylinders depend to a great extent on the friction generated at the seals, the friction characteristics have not been widely studied. Both the literature and manufacturers' catalogues rarely discuss the friction characteristics of pneumatic cylinders, and the lack of friction models limits the design, optimisation, and analysis of pneumatic cylinder systems. In seeking to improve the characteristics of pneumatic cylinders and to clarify the friction phenomenon, this paper describes friction force measurement tests carried out in pneumatic cylinders of six different diameters, from 32 to 100 mm. An experimental apparatus was designed to assess the effect of a broad range of operating conditions, where the velocity and pressure of the cylinder chambers are controlled independently. Measurements of friction force are shown for velocities of up to 0.5 m/s and pressures of up to 0.8 MPa. The data obtained will be useful for developing a suitable friction model, and the experimental apparatus will allow study of the effects on the friction force of different types of seal, lubricant, and cylinder barrel.

The paper deals with a system able to perform a single uniform scan acquisition of the Shroud.

A study was carried out to evaluate behavior and performance of vortex triodes. In particular, the study investigated the geometries and operating conditions which minimize the control flow capable of intercepting the supply flow. The study was conducted experimentally using a specially designed test bench on prototypes operating with water. The geometric parameters which influence vortex valve performance were identified and varied so as to minimize the ratio between control and supply flows. The paper presents a semi-empirical formula to predict vortex valve performance. In particular, the formula takes valve outlet geometry and the shape of outlet diffusers into account.

The paper describes design, construction and experimental testing of an active gait orthosis intended to assist locomotion in paraplegic subjects. Design specifications were formulated on the basis of an analysis of the context in which the device will be used. Different joint activation solutions were then proposed and examined. Considerable care was devoted to defining the logic and control system and to implementing the electro-pneumatic circuit, given that the system must be worn by a disabled subject who has no sensory perception in the lower limbs. Experimental tests, which made it possible to determine system performance at each step of development, were carried out with no user, then with a healthy user and finally with a paraplegic user. Experimental results consisting of graphs and photographic images are presented and discussed.

The journal equation of motion and the complete Reynolds equation of compressible fluid film are numerically solved and a computer program is developed. The formulas are for externally pressurized bearings, but results are shown only for self-acting bearings. For certain cases, the validity of the theoretical results is verified by comparison with the experimental data available from the literature. Through intensive use of the program, journal center trajectories are obtained and effects of fluid inertia are investigated. New stability parameters are presented and stability diagrams are established for bearings with L/D = 0.25, 0.5, 1, 1.5, and 2. The rotor unbalance effects on bearing stability limits are illustrated for several cases.