Software and Hardware Implementation of a Microtorquemeter Matteo Giunta University of Catania Department of Industrial Engineering Viale A.Doria 6, 95125, Catania, Italy Email: matteo.giunta@studium.unict.it Abstract—The present work aims to improvement hardware the maximum torque exerted on the tool and the angle of and software of a torque-meter able to perform static and the channel in which the instrument works. To increase the dynamic tests of Ni-Ti instruments for root canal treatment. torsion fracture and the angle before the occurrence of the Based on ISO 3630-1 standards, the device provides the real- time measurement of the torque, exerted on the various types of failure, more advanced machining techniques are designed endodontic instruments by a servo-controlled motor, as a function (EDM, CM-wire, M-wire) [10]–[12] and new design to keep of the shaft rotation angle. The standards require the use of a the shape of the channel as constant as possible. In effect, it low-speed motor (2 rpm) and the connection of the root canal was demonstrated that, before fracture, the tool is twisted on instrument between two chucks. The torque-meter is composed itself [13], therefore it is tried to have instruments in which by a stepper motor operating on a lever with equal arms. The first one drives a chuck transmitting the torque to the base of this winding is manifested after a larger rotation possible. To the root canal instrument, while the second one is connected on measure these two values, different machines have been made one side to a pulley, connected to a second chuck that allows to test to failure endodontic instruments [14], [15]. In them, the locking of the free end of the root canal instrument. In this the tool tip is locked, while the base is set in rotation at a work the hardware was improved by a modern real-time NI-PXI constant speed up to failure. In the laboratories of Mechanical Platform, mounted on a 64-bit PC, on which it was implemented, in LabVIEW environment, a software that merges the reading Engineering of the Catania University was developed a testing of data from load cell and encoder and the management of the machine capable of providing the failure torque values and stepper motor. In order to verify the efficiency of the new device, the angle at which it occurs. The use of such a device has the same type of endodontic instrument previously tested by the produced numerous scientific publications [16]. To enable this old one, was analyzed. The results were compared by highlighting category of testing devices to accurately operate, is necessary a remarkable improvement of measurement accuracy. each time obtain a correct synchronization between the various I. I NTRODUCTION measured quantities [17], [18]. The objective of this study was to improve the testing machine by implementing both The study of endodontic instruments (files) is a continually hardware and software. The device in question was realized growing and, by keeping up with the innovations of technology according to the parameters specified by ISO 3630-1 (2008). and materials, even the testing machine that allows to study the behavior they have undergone significant changes. This II. E NDODONTIC INSTRUMENTS TESTING MACHINE to make more accurate the study of their response to the The principle for testing of torque resistance of root canal mechanical stresses to which the clinical application submits instruments is based on measurement of their torque and them [1]. The most significant change of files took place angular deformation during a test [19]. To measure the torque mainly in the choice of materials to be used, going from on the files a torque tester is designed and manufactured that, stainless steel to alloys in Ni-Ti [2]. This step led to an based on the ISO 3630-1 standard, provides the real-time increase of the force that can be exercised on the files and measurement of the torque exerted on the various types of files to a greater flexibility but, at the same time, have made them by a servo motor. To measure the torsion on the root canal more vulnerable to breaking [3], [4]. Although in clinical instruments a torque-meter has been designed and realized practice the instruments failure rate is 5% [5], a study has which, based on ISO 3630-1 standards , provides the real- proved that the tools made of Ni-Ti break seven times more time measurement of the torque exerted on the various types frequently than those made of stainless steel [6]. The causes of files by a servo-controlled motor. This choice was dictated of failure are due to the exerted torque and the stress caused by the guidelines of ISO (Fig. 1a), which require the use of a by typical cyclic actions of rotational tools [7]–[9]. In the low-speed motor (2 rpm) and the connection of the root canal first case, the elements characterizing the phenomenon are: instrument between two chucks. The testing machine exploits the operating principle of the precision balance (Fig. 1b). This Copyright c 2016 held by the author. consist of a yoke with equal arms that allows carrying out the indirect comparison between the torque produced on the 15 (a) (b) Fig. 1. (a) ISO 3630-1 scheme, (b)precision balance scheme. application in this testing device. In effect, did not ensured the necessary flexibility and lead immediately to breaking of files. It was, therefore, necessary to create a custom-made load cell. For the excellent characteristics of mechanical resistance, high elasticity and recovery of the silicone, the strain gage cell was made by placing a strain gage between two silicone strips of 1 mm thickness (Fig. 3). The two ends of the strain cell were fixed on one side to the rocker arm and the other to the base. It was necessary to carry out careful initial calibration to define the response curve of the instrument as a function of the applied loads (µm/m/N ). The calibration law is shown in Fig.4. The actuation system consists of a bipolar stepper motor Fig. 2. Testing Machine. (Sanyo 103 - H7123 - 5040) and a board Phidgets Stepper Bipolar 1 - Motor 1063, which allows to control the position, velocity and acceleration of stepper motor. In order to be able endodontic instrument by the stepper motor and the resisting torque misurate by strain gage load cell. This device, shown in Fig. 2, is composed of a stepper motor, which controls a chuck that transmits the torque to the root canal instrument, and of the yoke at equal arms that is connected on one side to a pulley, the other side is rigidly attached to a custom- made load cell, in turn connected to the base. The pulley is connected, via a shaft, to a second chuck which allows the locking the free end of the root canal reamer. Finally, the root canal instrument is clamped between the two chucks: the first, integral with the drive shaft, transmits the torque; the other, connected by the torque transducer to the strain gage load cell, returns the resistant torque. F1 = F2 Mt = F2 R The load cell provides the value of the force F2 that is equal and opposite to the force F1 exerted by the steel wire connected to the pulley. Then, F1 note, you get the value of the torque as the product of the F1 multiplied for pulley radius R. This torque is the one that brings the tool to failure. Commercial available load cells were not suitable for Fig. 3. Custom-made load cell. 16 Fig. 5. Chuck details Fig. 4. Second degree equation obtained with calibration. to remove between their chucks in the mounting phase of the endodontic instrument and bring them in the working phase, the motor shaft has been replaced by two coaxial shafts. The interior is fixed to the motor shaft, the outer slides on the first and is tightened with a locking screw once the desired position is reached. In this way it is therefore possible to space the chucks during assembly and approach them in that work. The gripping of the instrument to 35 mm from the tip is ensured by a reference needle, consisting of a plate integral with the base and a double flat groove formed on the shaft outer diametrically opposite generatrices. These latter covering the dual function of the reference point for clamping to 5 mm and a flat key of the attachment section to tighten the chuck motor side (Fig. 5). Fig. 6. Switch circuit scheme. Since the electric engine is controlled by the hardware card with a preset rotation to a value much higher than that of the structure with the load cell of the testing machine and to tested tool breakage, the shaft would continue to rotate after output the value of the deformation of the same in m/m. the breakage occurred, making it impossible for an accurate The software that allowed the management of the controller reading of the angle. It is therefore designed a system to has been developed entirely in LabVIEW installed on a PC shut off the power at the exact time of the file breakage. with a 32-bit operating system. The only purpose of the This system, shown in Fig. 6, is based on an electric circuit software for data acquisition was to take the signal from the obtained by connecting a power supply pole of the stepper control unit, convert it in Newton and create a report file motor between the two chucks, in this way the endodontic with the data relating to the test. These were then manually instrument acts as a switch. As long as it remains intact, the processed, together with the encoder data acquired through circuit is closed and the shaft rotates; as soon as failure occurs, a NI Card 6009, to obtain the graphs that relate torque and a return spring brings the two sliding shafts in the rest position angle. Moreover, in this case, the electric motor was connected [20], separating the two parts of the endodontic instrument. to the system via USB and the software used to manage it, In this way the circuit is interrupted and the motor stops. In provided by the same manufacturer, worked in parallel with order to associate a rotation angle to the torque necessary to the system developed in LabVIEW. With this work it was generate the breakage of the file, the motor shaft has been made the transition to a modern NI-PXI Platform mounted equipped with a two channel optical incremental encoder (HP on a 64-bit PC on which it was implemented, in LabVIEW - HEDS 5500). environment, a software that has merged the reading of data from strain gage cell and encoder and the management of III. S OFTWARE IMPLEMENTATION the stepper motor. Regarding the motor, the transition from Before this study, data obtained from the strain gage cell dedicated software to LabVIEW was trivial since the company and encoder were acquired and processed in Excel at a later that produces the card that manages the motor also provides stage. Load cell data were read via the National Instruments libraries for LabVIEW that contain the subVIs needed to SCXI 1600 strain module, able to create a Wheatstone bridge manage the various parameters. The issue was different for the 17 Fig. 7. (a) ”For” loop, (b) ”While” loop management of the load cell and encoder. In the new system, was wrote a code, in a subVI, which allows the solution we have two data streams (the force from the strain gage cell to the second-degree equation obtained during the load cell and the rotation from the encoder) and the engine management calibration. Once these operations have been performed, the so it had to create a more complex software. This works in individual readings are inserted into an array. This is, then, two distinct phases. In the first, the motor remains stationary, filtered through a low-pass filter to obtain the noise-free signal. in the second, its actuated. In the first phase, channels from At the same time the data from the encoder are acquired. The which read data are initialized and the reading procedures have incremental rotary encoder used has a quadrature output, is been created. Moreover, always with the engine stopped, 2500 able to rotate at a maximum speed of 30,000 rpm and with a samples are taken from the load cell (Fig. 7a). What it read in resolution of 500 pulses per revolution. This type of angular this case, when the load is absent, are the values of the signal speed transducers is designed for direct mounting of drive noise. To make it less influential it is then made the mean of shafts, and are capable of producing two digital waveforms the 2500 values that, in the second phase of the program, was with 90 phase shift. This provides information on resolution subtracted to the single value read from the load cell. In the and direction. The acquired data are in degrees and, as occurs second phase, takes place the acquisition of data from the load for the strain gauge cell, the individual readings are inserted cell and encoder and the noise study. Since the aim of the study in an array. This, together with the array of the data obtained is to have the torque/angle data pairs, it was decided to take from the strain gauge cell, are combined into a cluster of arrays the data through two parallel processes, creating two different from which is generate a graph (Fig. 9). Another improvement arrays of data both from the encoder readings and from the involved the export of data. This was previously done by load cell. Then, these are merged to creating a cluster of arrays the LabVIEW’s VI called ”Write to measurement file” that from which directly extrapolate the complete test graph that exported to an Excel spreadsheet the arrays of data obtained correlates the torque (expressed in Ncm) and the rotation (in in the form of columns. In this study was realized a report file degrees). For this purpose, it was necessary to set the reading that not only exports data but also creates graphs and performs of data to have only one value of the rotation angle coupled to some data elaboration needed for the study. a single value of the force. Therefore, we have opted for the IV. DATA ANALISYS acquisition of the data on demand. In fact, the encoder, unlike the load cell, is too slow compared to the speed of acquisition For the analysis and processing of experimental data it of the data that the acquiring unit allows to have. From the data was decided to use Excel. The load cell data are saved by collected before synchronizing the devices, it was noted that LabViews File Report in a file *.xls, where three columns the encoder returned the same angle for different force values of data are created. These report, respectively, the angle of read from the load cell. Since, as shown in Fig. 8, these values rotation (degrees), the deformation (m/m) of the strain gauge were very close to each other (in the order of thousandths of load cell and the force (N) transmitted from the balances arm N), it is chosen to insert the two instances of measurement to the load cell during the test. The deformation measured by within a single while loop (Fig. 7b). This loop operates with the load cell is due to the force that the pulley radius (R = 1 the frequency of 1 cycle every 20 ms, which made the reading cm) transmits to the steel cable. Therefore, the strength values exclusively dependent by a parameter that can be modified as are equivalent to the torque values expressed in Ncm. With necessary. the torque and angle values, it is possible to realize a chart that correlates the torque applied to the tip of the endodontic However, data acquired from the load cell, are referred to instrument with its rotation until the breakage. Prior to this the deformation of the strain gage load cell and are expressed study, the graph obtained was of the kind shown in Fig. 10. In in m/m, then must be converted into Newton. To do this, the first part of the curve, it can be seen a lag phase due to the 18 Fig. 8. Data example. Fig. 9. Graph obtained in the front panel. fact that the operator had to first start the software to acquire data and then start the engine by using a different software. Moreover, there was also a delay due to the compilation of the program that controlled the engine. Because of this initial Fig. 10. Graph obtained with the previous system. delay the graph does not show an accurate value of the rotation angle. With the encoder use we achieved a substantial improve- ment in data processing. With the new system, in fact, the values of the load cell are directly coupled to those of the encoder. In addition, being the new one a system based on a unique software that manages all parts of the testing machine, we have no more delays due to the use of different softwares. In general, the transition to a more modern and faster system has brought a saving in terms of test time duration. Clearly, the time required to rotate the instrument until the break remained unchanged since the speed of rotation is always the same. What is considerably changed is the time used in Fig. 11. Graph that shows the noise frequency. the test preparation operations. In fact, the time required to calibrate the load cell before each test was reduced making this an almost immediate operation. Another improvement is to the strain gauge cell input data (Fig. 11). Thanks to the regarding the noise present on the signal. As it can be seen filtration was obtained significantly more accurate graphics as from the graphs, the data provided by the new software, are it can be seen from Fig. 12. This figure shows the graphs of virtually noise-free. This improvement was achieved thanks to two tests performed on the same type of endodontic tool (F6 the noise frequency study, which it allowed to set the low-pass SkyTaper 25 mm length, 6% taper), at the top there is the filter that processes the data received from the load cell. Noise graph obtained with the old system and below there is the frequency was identified by applying the Fourier transform graph obtained with the new one. 19 Fig. 12. Comparison between graphs obtained with old and new system. V. C ONCLUSIONS [2] S. Thompson, “An overview of nickel–titanium alloys used in dentistry,” International endodontic journal, vol. 33, no. 4, pp. 297–310, 2000. The present study has contributed to improving a previously [3] H. Walia, W. A. Brantley, and H. Gerstein, “An initial investigation of realized testing device. This machine was created as a part of the bending and torsional properties of nitinol root canal files,” Journal of endodontics, vol. 14, no. 7, pp. 346–351, 1988. a larger research program performed in co-operation between [4] F. Lo Savio, E. Pedullà, E. Rapisarda, and G. La Rosa, “Influence research groups of Engineering and Medicine departments of of heat-treatment on torsional resistance to fracture of nickel-titanium the Catania University on the behavior of Ni-Ti instruments endodontic instruments,” Procedia Structural Integrity, vol. 2, pp. 1311– 1318, 2016. for root canal treatment. The realization of this torque-meter, [5] S. B. Alapati, W. A. Brantley, T. A. Svec, J. M. Powers, J. M. Nusstein, based on ISO 3630-1 standards, was possible thanks to a and G. S. Daehn, “Sem observations of nickel-titanium rotary endodontic careful optimization performed as well as on the individual instruments that fractured during clinical use,” Journal of Endodontics, vol. 31, no. 1, pp. 40–43, 2005. components and on a global device. Particularly, the choice of [6] M. K. Iqbal, M. R. Kohli, and J. S. Kim, “A retrospective clinical the material and of the geometry with which it was realized study of incidence of root canal instrument separation in an endodontics the strain gage load cell (suitable for the measurement of a graduate program: a pennendo database study,” Journal of endodontics, vol. 32, no. 11, pp. 1048–1052, 2006. low-torque amount without providing an excessive torque), [7] E. Pedullà, F. Lo Savio, S. Boninelli, G. Plotino, N. Grande, E. Rapis- the torque transmission system and the mounting of the arda, and G. La Rosa, “Influence of cyclic torsional preloading on instrument on the chucks. The further implementation made cyclic fatigue resistance of nickel–titanium instruments,” International endodontic journal, vol. 48, no. 11, pp. 1043–1050, 2015. in this study involved both the hardware and the software. The [8] E. Pedullà, F. Lo Savio, G. Plotino, N. M. Grande, S. Rapisarda, previous hardware has been improved by the use of the NI-PXI G. Gambarini, and G. La Rosa, “Effect of cyclic torsional preloading Platform, which gives the possibility to acquire in real time on cyclic fatigue resistance of protaper next and mtwo nickel–titanium instruments,” Giornale Italiano di Endodonzia, vol. 29, no. 1, pp. 3–8, the output signals from sensors and especially to synchronize 2015. with each other. The new software has merged the reading of [9] P. Parashos and H. H. Messer, “Rotary niti instrument fracture and its data from strain gage cell and encoder and the management of consequences,” Journal of Endodontics, vol. 32, no. 11, pp. 1031–1043, 2006. the stepper motor. In this way, there are no longer delays due [10] E. Pedullà, F. Lo Savio, S. Boninelli, G. Plotino, N. M. Grande, to the use of different software. Along with this improvement G. La Rosa, and E. Rapisarda, “Torsional and cyclic fatigue resistance of was been joined the system’s ability to process a development a new nickel-titanium instrument manufactured by electrical discharge machining,” Journal of endodontics, vol. 42, no. 1, pp. 156–159, 2016. in FFT of the plotted signal. In fact the use of advanced soft [11] Y. Gao, V. Shotton, K. Wilkinson, G. Phillips, and W. B. Johnson, computing techniques has became progressively an effective “Effects of raw material and rotational speed on the cyclic fatigue of option in many contexts [?], [?], [21]–[23]. Thus, it is possible profile vortex rotary instruments,” Journal of endodontics, vol. 36, no. 7, pp. 1205–1209, 2010. to derive the main frequency of the electronic noise and, by [12] Y. Shen, H.-m. Zhou, Y.-f. Zheng, B. Peng, and M. Haapasalo, “Current means of a low-pass filtering, clean up the signal, improving challenges and concepts of the thermomechanical treatment of nickel- the accuracy. The good performances of the device have been titanium instruments,” Journal of endodontics, vol. 39, no. 2, pp. 163– 172, 2013. highlighted by both the result of the tests performed on the [13] A. M. Elnaghy and S. E. Elsaka, “Torsion and bending properties of root canal instruments, which are in good agreement with the oneshape and waveone instruments,” Journal of endodontics, vol. 41, values found in the technical literature, as well as for the no. 4, pp. 544–547, 2015. [14] G. S.-P. Cheung, S.-H. Oh, J.-H. Ha, S. K. Kim, S.-H. Park, and H.- quality of the graphics, compared to ones obtained using the C. Kim, “Effect of torsional loading of nickel-titanium instruments on old system. cyclic fatigue resistance,” Journal of endodontics, vol. 39, no. 12, pp. 1593–1597, 2013. R EFERENCES [15] B. Sattapan, J. E. Palamara, and H. H. Messer, “Torque during canal instrumentation using rotary nickel-titanium files,” Journal of Endodon- [1] S. R. Drake, D. M. Wayne, J. M. Powers, and K. Asgar, “Mechani- tics, vol. 26, no. 3, pp. 156–160, 2000. cal properties of orthodontic wires in tension, bending, and torsion,” [16] G. La Rosa, F. Lo Savio, E. Pedullà, and E. Rapisarda, “Developing of American journal of orthodontics, vol. 82, no. 3, pp. 206–210, 1982. a new device for static and dynamic tests of ni-ti instruments for root 20 canal treatment,” Procedia Structural Integrity, vol. 2, pp. 1303–1310, 2016. [17] M. Calı̀ and F. Lo Savio, “Accurate 3d reconstruction of a rubber mem- brane inflated during a bulge test to evaluate anisotropy,” in Advances on Mechanics, Design Engineering and Manufacturing. Springer, 2017, pp. 1221–1231. [18] G. Sequenzia, S. Oliveri, and M. Calı̀, “Experimental methodology for the tappet characterization of timing system in ice,” Meccanica, vol. 48, no. 3, pp. 753–764, 2013. [19] M. Bonfanti, G. La Rosa, and F. Lo Savio, “A laser optical torquemeter for measuring the mechanical power furnished by a chirale turbine,” in Merida-DL Tentative. International Society for Optics and Photonics, 2005, pp. 74–81. [20] G. Sequenzia, S. Oliveri, M. Calabretta, G. Fatuzzo, and M. Cali, “A new methodology for calculating and modelling non-linear springs in the valve train of internal combustion engines,” in SAE Technical Paper. SAE International, 04 2011. [21] F. Bonanno, G. Capizzi, and G. Lo Sciuto, “A neuro wavelet-based ap- proach for short-term load forecasting in integrated generation systems,” in Clean Electrical Power (ICCEP), 2013 International Conference on. IEEE, 2013, pp. 772–776. [22] F. Bonanno, G. Capizzi, S. Coco, A. Laudani, and G. Lo Sciuto, “A coupled design optimization methodology for li-ion batteries in electric vehicle applications based on fem and neural networks,” in Power Electronics, Electrical Drives, Automation and Motion (SPEEDAM), 2014 International Symposium on. IEEE, 2014, pp. 146–153. [23] D. Gotleyb, G. Lo Sciuto, C. Napoli, R. Shikler, E. Tramontana, and M. Woźniak, “Characterisation and modeling of organic solar cells by using radial basis neural networks,” in International Conference on Artificial Intelligence and Soft Computing. Springer, 2016, pp. 91– 103. [24] M. Wozniak, C. Napoli, E. Tramontana, and G. Capizzi, “A multiscale image compressor with rbfnn and discrete wavelet decomposition,” in International Joint Conference on Neural Networks (IJCNN). IEEE, 2015, pp. 1219–1225. [25] C. Napoli and E. Tramontana, “Massively parallel wrnn reconstructors for spectrum recovery in astronomical photometrical surveys,” Neural Networks, vol. 83, pp. 42–50. 21