## 1 Introduction
### Novel Approach toward Digitalization  
Being fully manual, both referred protocols present a series of problems: (i) lack of positioning accuracy--due to inadequate moving of test equipment, involving manual tightening and untightening screws and sliding profiles with human visual criterium; (ii) \begin{table}
\begin{tabular}{c c} \hline \hline
**N.** & **Description** \\ \hline
1 & Draw a grid pattern in the upper surface of the block with the position where the electrodes will align. \\
2 & Apply marble paste to where the electrodes contact the surface. \\
3 & Unscrew the support brackets and slide the profile holding the electrodes to the specified position and tighten the screws. \\
4 & Turn on the power supply to the specific current value. \\
5 & Register with a voltmeter the values of the voltage electrodes and their location. \\
6 & Turn off the power supply. \\
7 & Repeat all of the above steps until completing the entire block. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Electrical tomography protocol. Figure 3: Dipole–dipole. highly time consuming--the time needed to complete all the readings on a medium-size block is very high, as the operator must perform a significant number of repetitive tasks with high probability of failures; (iii) absence of a digital medium--all test results and their locations are not on a standard digital format but depend on the recording preferences of the operators; this means that their integration in any analytical software and its use in a different phases of the stone-producing process becomes extremely time consuming. With all the above referred constraints, the process used to overcome the results uncertainty and to obtain a statistical measure of the results quality is to repeat the test multiple times and perform a statistical analysis, making the process even harder and longer lasting. Trying to improve the existing procedures for collecting stone information and data exporting, a novel approach was developed by the authors. As stated earlier, the existing method for performing ultrasonic and electric tomographies possesses a lot of problems that make it practically invisible for gathering stone data. A fine analysis of the reported problems allows recognizing a pattern where most of the problems are caused by human interaction, which is aggravated by the use of inadequate structure. All indicators point to the need of designing a new fully automated structure that although controlled by an operator is capable of positioning the testing equipment precisely according to a specified virtual grid pattern, triggering the input readings at the correct time, acquiring the results, and exporting the digital data, all of this without human interaction, completely eliminating all of the uncertainty associated with human performance and therefore increasing the efficiency of the overall system. The proposed prototype is able to accept sample blocks with limited and known dimensions. The system was developed in order to comply with the following constraints: (i) it must divide the block into sections spaced 5 mm apart from each other, on the \(X\)-axis (see Figure 1) and at each location, it should be able to perform a resistivity tomography and a series of ultrasonic tomographies (10 mm apart from each other, along the \(Z\)-axis); (ii) related to electric tomographies, the electrodes must move along two different axes, along X for positioning the electrodes in the correct section and along Z for electrical contact electrodes surface; (iii) related to ultrasonic tomography, the transducers must move along three different axes, along X and Z for correct positioning and along Y to gently press the sensors against the rock surface. Therefore, the new developed system must have three degrees of freedom (X, Y, Z) provided by high-accuracy linear actuators. The autonomous control of the system is assured by a Programmable Logic Controller (PLC) that manages the linear-positioning actuators, the input sensors (electrodes and transducers), and acquires the resulting data.