E Pennestrì

A Review of Formulas for the Mechanical Efficiency Analysis of Two Degrees-of-Freedom Epicyclic Gear Trains

This paper after a rigorous proof of the formulas originally proposed by Rodzimovsky, demonstrates the numerical equivalence of the different approaches available for computing the mechanical efficiency of two degrees-of-freedom (d.o.f.) epicyclic gear trains. The paper includes also a discussion on the redundancy of data required by some formulas.

Using a Virtual Dummy to Simulate Vibration Dose Value for Different Car Occupants

The comfort assessment for car occupants is not an easy task to achieve. It is a matter of personal perceiving, thus a solution which may seem comfortable to one could be not to another. Moreover it is a field which requires knowledge both from science and medicine. The vibrational comfort analysis is the topic of this paper. There are different international standards to define the vibrational comfort through computed indices. In particular the British Standard BS 6841 (1) introduces the Vibration Dose Value (VDV). The main idea which lies behind the VDV is to estimate the whole body vibration. In fact the standard suggests the main locations for acceleration measurement (feet, seat and back) and their direction axes. The overall number of acquisitions is twelve. A numerical code for the vibrational comfort analysis of car occupants, estimating the VDV for each of them, has been developed. The code, named DAViD, is based on a multibody approach (2). It has been validated by means of experimental tests (3,4). In this paper the influence of the anthropometric features (height and weight) and the inclination of the backrest on the VDV has been investigated. The code is an useful tool for predicting at the seat design level the vibrational discomfort.

Mechanical Efficiency Analysis of a Cardan Joint

This investigation concerns with the mechanical efficiency of Cardan joints. The model includes also the effects due to manufacturing and mounting errors and the influence of rotation speed on the efficiency. The joint has been modeled as an RCCC spatial linkage and the full dynamic analysis performed by means of dual vectors algebra.Copyright

A DYNAMIC SIMULATION OF CAM ACTUATED ROBOTIZED GEARBOX

In this paper a simulation of the cam actuator of a robotized gearbox is presented. The actuator is a barrel cam which moves a pin according to a prescribed motion law. The model of contact, between cam and follower, is based on a finite elements approach of the theory of beam on continuous elastic foundation, modified by the authors to include the effect of shear on the deformation and dynamic effects. The foundation modulus is computed using Hertz theory taking also into account the change of principal curvature values during the relative motion between cam and follower. This model has been embodied in a complete gear shifting simulation in order to compare the effects on contact forces, wear actions and shifting time of different cam profiles.

Kinematic Analysis of the Antikythera Gear Mechanism by Means of Graph Theory

The Antikythera mechanism is one of the most extraordinary examples of the degree of sophistication reached by the Hellenistic culture in the field of mechanism design. This calendar mechanism not only witness the degree of astronomic knowledge of the greeks, but also their capability to conceive and build marvelous mechanical devices. The mechanism is the first documented example of differential gear arrangement in western culture. The paper gives first a description of the kinematic structure of the mechanism in terms by means of a graph, then a full kinematic analysis of this complex gear train is performed. The results of our kinematic analysis, only partially coincident with those obtained by De Solla Price, match very closely the discoveries made by the Greek astronomer Hipparcus about the duration of the lunar months. There is also a conjecture on the kinematic structure and gear dimensions of some of the missing parts. In the Appendix is reported the listing of the Maple program developed for the kinematic analysis.Copyright

Computer aided reconstruction of italian ancient clocks

Italy has plenty of cultural heritages. The masterpieces are often placed in locations which are difficult to reach, moreover many artifacts, coming from man’s creativity, have very complex functioning. The authors of this paper describe their experience in using the computer graphics capabilities in order to reproduce four ancient clocks functioning coming from different Italian regions. The study is based not only on the 3D-shapes reconstruction but also on the simulation of their complex mechanisms in order to mimic their functioning. The realism of the reconstruction allows to use the graphical products in exhibits, museums and also for maintenance programs. The rendering techniques together with an accurate camera path, allow to get into the clock mechanisms and to appreciate all the features (and even secrets) that a simple glance cannot reveal.

On the reliability of some numerical methods in kinematic analysis

A numerical finite differences algorithm, given by a first differentiation formula and that can be used for repeated differentiations, has been deduced on the basis of an approximation technique that makes use of Gram’s orthogonal polynomials. The algorithm itself has been compared with other numerical procedures suggested by other authors. It has been demonstrated how the calculus reliability discussed is foreseeable when transfer functions of the algorithms are considered.