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This paper proposes a method to experimentally identify the main modal parameters, i.e., natural frequencies and damping ratios, of an aerostatic spindle for printed board circuit drilling. A variety of methods is applied to the impulse-response function of the spindle in the presence of zero rotational speed and different supply pressures. Moreover, the paper describes the non-linear numerical model of the spindle, which consists of a four-degree-of-freedom (DOF) rigid and unsymmetrical rotor supported by two aerostatic bearings. The main goal of the work is to validate the developed non-linear numerical model through the proposed identification procedure and the performed experimental tests. The comparison proves satisfactory, and the possible sources of uncertainty are conjectured.

Even though the behavior of aerostatic bearings has for long been the topic of extensive research, there are still many aspects that require further investigation. Among these, the identification of the discharge coefficients is one the most crucial. This paper presents a hybrid method to identify the discharge coefficients of aerostatic bearing orifices. The method is termed as hybrid since it exploits experimental data and the equations of the analytical model of a circular and centrally fed aerostatic pad. The obtained results demonstrate the accuracy of the method. The proposed method further offers practical advantages compared to the conventional methods.

This paper presents the analysis of the static and dynamic performance of a passively compensated air pad. The proposed method consists in the integration of a custom-built diaphragm valve and a commercial aerostatic pad. A lumped model is used to simulate the static and dynamic performance of the pad. Results demonstrate that the proposed method is very effective when the system works with excitation frequencies below 10 Hz.

Friction and wear are tribological phenomena that have produced significant economic damage and environmental issues throughout our history. Different kinds of lubricants and coatings have been employed in the attempt of reducing friction losses. Because of their remarkable performance, gas lubricated systems are characterized by almost zero friction and wear. For this reason, they can be utilized in applications where rolling and fluid bearings cannot, e.g., metrology, medical equipment and tool machine. This paper reviews the evolution of gas lubrication through history. The topography of the subject is described from its origins to how it was shaped over the centuries, trying to preserve the logical cause and effect relationship of the events. For the sake of consistency, the review considers only the key past contributions which are strictly related to gas lubrication.

Because of their almost zero friction, cleanness and long life, aerostatic bearings are commonly used in many applications where high precision of positioning is required, e.g. machine tools, measuring machines, semiconductor manufacturing and power board testing. However, air bearings suffer from low relative stiffness and poor damping. Active and passive compensation are two effective methods to enhance the static and dynamic performance of these kinds of bearings. Despite their higher performance, active compensation solutions are too expensive to be used in industrial applications, as a consequence of the costs related to their controllers, actuators and sensors. This paper presents the design and performance of a passive compensation method that exploits a diaphragm valve. Thanks to its ease of integration, satisfactory performance and relatively low cost, this method could be a valuable solution to increasing the stiffness of aerostatic bearings. This work provides a procedure to design diaphragm valves depending on the type of the integrated pad and the desired nominal air gap height. Results demonstrate that, once correctly designed, the diaphragm valve makes it possible to obtain bearings with quasi-static infinite stiffness at the selected air gap height.

This paper shows the kinematic and dynamic model of a prismatic Delta robot designed for a 3D printer. After description of the direct and inverse kinematic algorithms, the forces on the actuated prismatic joints are computed with the lagrangian approach.

Aero-static thrust bearings are widely used in high precision conventional applications, e.g., in machine tools, measuring instruments, precise positioning systems, manufacturing and medical equipment. Their appeal is due to the absence of contact between moving and stationary parts, which ensures their low friction, limited heat generation and long life. Moreover, the use of air bearings usually does not contribute to the environmental contamination. However, aerostatic thrust bearings have usually lower stiffness and load capacity than rolling or oil bearings. For this reason, active and passive compensation are currently used to enhance these properties, thus extending the bearing's operating range. Recently, active compensation methods have become more popular thanks to improvements in mechatronics technology, and because they can provide the very high accuracy required by current high precision applications. This paper reviews the state of the art of the active compensation method and provides general classification criteria, outlining dissimilarities and the pros and cons of the available solutions. The paper concludes with several considerations and comments regarding the main performance features of each solution.

Thanks to their low friction, aerostatic pads have important applications in precision positioning systems and linear guides. A simple and cheap solution to increase the static stiffness of aerostatic pads is to add a proper designed pneumatic valve to regulate the air flow supplied to the bearing. However, integrating aerostatic pads with additional devices can reduce its dynamic performance. This paper presents a numerical study on the dynamic behaviour and stability a commercial aerostatic pad controlled by a custom-built diaphragm valve. The bearing performance is studied by means of a lumped parameters model. Air bearing stiffness and damping are analysed in the frequency domain. Subsequently, the lumped model is linearized to investigate the stability of the system by means of Routh-Hurwitz method. The performance of the controlled air pad is compared to that of a simple commercial air pad.

Numerical models have been largely utilized as a valuable tool to investigate the performance of aerostatic pads. These models make it possible to evaluate the effect of different parameters, e.g., supply pressure, orifices diameter and locations. This paper presents a numerical study to investigate to what extent the use of concave surfaces can modify the static performance of aerostatic pads. The study consists in comparing the performance of flat and concave pads in the presence of different supply pressures and maximum depths of concavity.

In the last fifty years, the performance of aerostatic pads has been largely investigated as regards load capacity, consumption, stiffness and damping. However, there are few works studying the effect of other aspects which are not usually taken into account, e.g., deformations, waviness and roughness. This paper investigates the causes of air leakages at zero air gap condition. Different numerical simulations are performed to evaluate which is the deformed shape of the pad under different loading conditions. Experimental air flow measurements at zero air gap condition were also performed. It has been found that, in this instance, pad deflection is one of the main causes producing air leakages.

Because of their low friction and wear, aerostatic pads are widely in many high precision applications, e.g., linear slides, coordinate measuring machines and medical equipment. However, especially grooved aerostatic pads can be unstable under certain operating conditions. This paper presents a lumped parameter model to study the static and the dynamic performance of a rectangular grooved aerostatic pad. The theoretical results are compared with the experimental ones.

Air pads are often embedded into robotic devices for manufacturing and measuring applications. Investigating the performance of these pads is essential to obtain robot characterized by very accurate motions and positioning. Due to their simplicity, mathematical lumped parameter models can be adopted to evaluate quickly both the static and dynamic performance of such bearings. This paper describes a lumped parameter model to study the behavior of a grooved rectangular air pads. The static and dynamic results of the model are validated by using a purpose-built test bench.

Aerostatic pads are successfully employed in linear systems where very accurate and precise positioning is required, e.g. machine tools and measuring equipment. Both the static and dynamic performance of many different types of aerostatic pads have been already numerically and experimentally investigated. However, literature does not present so many works that investigate the performance of rectangular aerostatic pads with multiple restrictors, especially as regards their dynamic features. This paper shows an experimental and a numerical study of the static and dynamic performance of a rectangular aerostatic pad with multiple orifices distributed on a supply rectangle. The paper investigates the effect of the orifices diameter, of their position and of the supply pressure on the pad performance.

Articular cartilage is a specialised, aneural and avascular connective tissue that lines the end of synovial joints. Its main functions are minimising friction and wear during the movements between the joint surfaces, and spreading and transmitting loads and shocks over a larger area within articulations. Many studies have been performed to shed light on the outstanding tribological features of this soft poroelastic material. However, despite the effort expended, many aspects remain unclear. This paper presents an experimental investigation on the effect of the load and static loading time over the frictional properties of adult bovine articular cartilage.

This work presents a prototype of a compensated aerostatic pad which consists in the integration of a commercial pad with a custom-built regulating pneumatic valve. The performance of the system is studied both in static and transient conditions. The stability and the capacity of compensation of the protype are proved performing step force tests. Moreover, the paper describes the lumped parameter model of the compensated pad. To take into account the compensating action of the valve, a distinctive numerical procedure was developed. Experimental and numerical results are in good agreement and demonstrate that once a suitable initial set-up is defined, the integrated regulating valve allows bearings with quasi-static infinite stiffness to be obtained.

Because of their almost zero friction and wear, aerostatic pads are widely used in applications where very precise positioning is required. However, this kind of bearing suffers from poor damping and low specific stiffness. This paper presents a new compensation strategy to increase air pad stiffness. This method exploits a custom-built pneumatic valve which can be easily integrated with any commercial pad. The design and the working principle of the proposed system are described and studied with the aid of a lumped parameter model. The effectiveness of the proposed compensation is numerically and experimentally evaluated. The results demonstrate that the solution represents a good and cost-effective method to enhance the static stiffness of aerostatic pads.

Active compensation is an effective method for increasing air bearing static and dynamic performance. This paper describes the design, modelling and experimental validation of an actively compensated externally pressurized gas bearing. The active compensation is obtained through the support compensation strategy. With this strategy, the system’s initial working position is restored by compensating for air gap variations through adjustments to the bearing vertical dimension. The described bearing consists in a conventional thrust bearing which is integrated with a multilayer piezoelectric actuator, a compliant mechanism and a digital controller. Nevertheless the non-linear nature of the air system, a simple linear model results to be an effective choice for neighbour of equilibrium conditions. Results demonstrate the good accuracy of the model and the system’s good capacity of rejecting external force disturbances.

Bell Beaker pottery spread across western and central Europe beginning around 2750 BCE before disappearing between 2200–1800 BCE. The mechanism of its expansion is a topic of long-standing debate, with support for both cultural diffusion and human migration. We present new genome-wide ancient DNA data from 170 Neolithic, Copper Age and Bronze Age Europeans, including 100 Beaker-associated individuals. In contrast to the Corded Ware Complex, which has previously been identified as arriving in central Europe following migration from the east, we observe limited genetic affinity between Iberian and central European Beaker Complex-associated individuals, and thus exclude migration as a significant mechanism of spread between these two regions. However, human migration did have an important role in the further dissemination of the Beaker Complex, which we document most clearly in Britain using data from 80 newly reported individuals dating to 3900–1200 BCE. British Neolithic farmers were genetically similar to contemporary populations in continental Europe and in particular to Neolithic Iberians, suggesting that a portion of the farmer ancestry in Britain came from the Mediterranean rather than the Danubian route of farming expansion. Beginning with the Beaker period, and continuing through the Bronze Age, all British individuals harboured high proportions of Steppe ancestry and were genetically closely related to Beaker-associated individuals from the Lower Rhine area. We use these observations to show that the spread of the Beaker Complex to Britain was mediated by migration from the continent that replaced >90% of Britain’s Neolithic gene pool within a few hundred years, continuing the process that brought Steppe ancestry into central and northern Europe 400 years earlier.

Conventional approaches to design aerostatic bearings are based on their static characteristics. However, dynamic predictions are fundamental in order to obtain very precise positioning since air bearings are frequently subjected to dynamic load variations. This paper presents a simple linear time invariant model for aerostatic thrust bearings and the related experimental identification procedure. The experimental procedure identifies the stiffness and damping coefficients of the air gap model. The model validation was obtained comparing the experimental and theoretical bode diagrams of the studied system. The comparison demonstrates that the model leads to good results when neighbours of equilibrium conditions are considered.

The author examines the effects of contemporary science and technology on individuals and the psychological and cultural mutations that can result, ranging from the physical dematerialization of people to the continuity existing between their psyches and their electronic devices. Within a framework of interrelationships between art and society, he develops a hypothesis about the role of the artist in society.