Il nuovo SI: cambia tutto perché nulla cambi - 2ª parte

Nella prima parte di questo articolo ho descritto l’impianto concettuale dello SI: la coerenza (le unità derivate si formano componendo quelle di base tutte con coefficiente unitario), la collocazione di qualsiasi unità nel sistema (mediante una settupla di esponenti delle unità di base), la disponibilità di multipli e sottomultipli (a coprire 48 ordini di grandezza), il battesimo di alcune unità derivate con nomi speciali (di solito in onore di un illustre scienziato). Ho anche illustrato la definizione in vigore allora (vecchio SI) delle sette unità di base. Dopo la pubblicazione, è accaduto l’atteso evento: il 20 maggio 2019 è entrato in vigore il nuovo SI. L’impianto concettuale rimane identicamente lo stesso, mentre cambiano le definizioni delle unità di base; più precisamente, cambia il modo stesso in cui sono definite, che fa loro perdere molto del loro primato nel sistema. In questa seconda parte, illustrerò i punti di debolezza del vecchio SI e gli avanzamenti tecnici che hanno permesso di superarli, per arrivare al nuovo SI ora in vigore.I described the conceptual frame of the SI in the first part of this paper: coherence (derived units are formed by composing the base units all with unit coefficients), coordinates of any unit within the system (by means of a 7-tuple of exponents to base units), the avilability of mulpitles and submultiples (covering 48 orders of magnitude), the naming of some derived units with special names (usually after eminent scientists). I also illustrated the definitions in force (old SI) of the seven base units. After publication, the awaited event occurred: the new SI entered into force on May 20th, 2019. The conceptual frame remains identical, while the base unit definitions change. More precisely, the very way they are defined changes, which relinquishes most of their supremacy in the system. This second part illustrates the weaknesses of the old SI and the technical breakthroughs that enabled to overcome them and to get to the new SI now in force

Il sistema tastatore a contatto: errori, cause, consigli

Le cause d’errore principali di cui sono affetti i sistemi tastatori a contatto sono l’anisotropia, cioè la risposta non uniforme in tutte le direzioni, e la deriva termica. Questo articolo esamina tali cause, e fornisce suggerimenti sul come minimizzarne e stimarne gli effetti

Calibration of a Master Gear

Questo rapporto tecnico descrive la taratura di un segmento di anello di un cuscinetto a sfere. L’INRIM ha progettato il segmento di anello che è stato quindi prodotto dalla MG Marposs S.p.a. di Torino. La taratura è stata eseguita con la macchina a coordinate CMM/ST001 dell’INRIM. Questo lavoro si colloca all’interno del Progetto DriveTrian (ENG56) come deliverable 2.2.3.This technical report describes the calibration of a ball bearing ring segment. INRIM designed the ring segment to be representative of bearing rings Ø > 1 m and MG Marposs S.p.a. (Turin, Italy) manufactured the workpiece. The calibration has been performed with the coordinate measuring machine CMM/ST001 at INRIM. The present work is related to the deliverable 2.2.3 of Drive Train Poject (ENG56)

Design, manufacturing and calibration of a large ring segment

Design concepts, manufacturing steps and calibration strategies of a large ring segment are reported in this contribution. The study aims at investigating the feasibility of using a ring segment for establishing the traceability of large diameter workpieces, primarily to quantify the influence of the workpiece surface and form. The ring segment embodies two nominally coaxial features: a cylinder and a torus. Both the cylinder and the torus are highly partial features, which poses a challenge for the calibration. The measurands to calibrate are defined in terms of intrinsic and location features, according to the model for geometrical specification and verification (EN ISO 17450-1). The adopted measurement strategies are described and preliminary calibration results are reported

1D measurement of coordinates in space: a novel apparatus

A novel instrument to measure the coordinate of a point in space is presented. It does so in isolation, i.e. without the aid of similar devices measuring the other coordinates, as it is usually the case with other coordinate instruments. The eventual goal is to achieve a full 3D measurement by replicating the device three times orthogonal to each other, with a target uncertainty of 50 μm over a volume of (10 x 10 x 5) m³ in harsh conditions

Dynamics modeling of CMM probing systems

The probing system dynamics is important for coordinate measuring machine (CMM) performance, particularly when probing in scanning mode. This is a typical situation e.g. in gear metrology, where the flanks are typically scanned. This may occur even without full awareness of the user, who may accept default values or choose with little understanding. This work presents a modelling of a contouring probe. The model is based on the characteristics of real probes; more specifically, continuous passive systems are considered, resulting essentially in second order 3D systems. The theoretical model is validated experimentally by scanning suitable surfaces exhibiting a range of slopes. The separation between static and dynamic effects is achieved by repeating the experiments at varying scanning speed, so that a same geometrical slope results in different temporal slopes – which the probing system dynamics is sensitive to. The model is oriented to define a good trade-off between the scanning speed and the measurement uncertainty