Article
A New Prototype for Automatic Identification of Stone Block
Internal Structure
Bernardo Anes
1,2,3
, Joao Figueiredo
1,4,
* and Mouhaydine Tlemçani
1
Citation: Anes, B.; Figueiredo, J.;
Tlemçani, M. A New Prototype for
Automatic Identification of Stone
Block Internal Structure. Appl. Sci.
2021, 11, 6630. https://doi.org/
10.3390/app11146630
Academic Editor: Manuel Armada
Received: 29 June 2021
Accepted: 16 July 2021
Published: 19 July 2021
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1
Mechatronics Department, ICT, University of Évora, R. Romão Ramalho 59, 7000-671 Évora, Portugal;
m44856@alunos.uevora.pt (B.A.); tlem@uevora.pt (M.T.)
2
Metal Viçosa Lda, 7250-909 Alandroal, Portugal
3
Marmetal—Marmores e Materiais de Construção S.A., 7150-101 Borba, Portugal
4
Mechatronics Department, IDMEC, University of Évora, R. Romão Ramalho 59, 7000-671 Évora, Portugal
* Correspondence: jfig@uevora.pt
Abstract:
Nowadays, the inner shape and economic viability of a stone block is dependent on the
skill and experience of the “expert” that makes predictions based on external observations. This
actual procedure is an extremely high empirical method, and when it fails, substantial work, time,
and money is wasted. At present, researchers are committed to developing models to predict the
stone block internal structure based on non-destructive tests. Ultrasonic tomography and electrical
resistivity tomography are the tests that best fit these objectives. Trying to improve the existing
procedures for collecting stone information and data exporting, a novel approach to perform both
tomographies is proposed in this paper. This novel approach presents sound advantages regarding
the current manual procedure: namely, (i) high accuracy due to a new automatic positioning system;
(ii) no need for highly skilled operators to process measurements; (iii) measurements are much easier
to derive, and results are quickly delivered. A comparison between the new automatic process and
the current manual procedure shows that the manual procedure has a very low accuracy when
compared to the new developed automatic system. The automatic measurements show extremely
significant time savings, which is a relevant issue for the future competitiveness of the stone sector.
Keywords: marble industry; PLC; mechanical design; automation; SCADA
1. Introduction
1.1. The Marble Industry Context
Marble is highly used as a building material in construction due to its aesthetics,
durability, and long-lasting characteristics [
1
–
3
]. Usually, marble slabs last as long as
the buildings in which they were incorporated. This characteristic has motivated an
increasingly high demand for this resource world-wide followed by a growing production
quantity, reaching more than 150 million tons of ornamental natural rock in 2019 according
to [
4
]. This means that the marble industry plays an important role in the economic structure
of many countries. A considerable part of the quarrying and processing activities, in this
industry, are performed worldwide by small and family-owned companies, which have
a limited financial budget for investing in new techniques and machinery. This financial
constraint leads to the use of less efficient methods, generating high production costs and
significant waste of raw material. The most common method used to process marble goods
starts with the quarrying of large marble blocks, which according to [
5
] are separated from
the rock face by means of straddle bearing or explosions. Then, smaller portions are cut
from the main block, using traditional cutting techniques, involving diamond wire saws
that make linear cuts in the rock. The newly cut slices undergo a second stage of processing
in which the blocks are separated by their geometric characteristics, external appearance,
and cut into smaller slabs and tiles. The final stage involves polishing treatments and
preparation for commercial use. This complete production process originates a considerable
Appl. Sci. 2021, 11, 6630. https://doi.org/10.3390/app11146630 https://www.mdpi.com/journal/applsci
