=Paper=
{{Paper
|id=Vol-1730/p03
|storemode=property
|title=Software and Hardware Implementation of a Microtorquemeter
|pdfUrl=https://ceur-ws.org/Vol-1730/p03.pdf
|volume=Vol-1730
|authors=Matteo Giunta
|dblpUrl=https://dblp.org/rec/conf/system/Giunta16
}}
==Software and Hardware Implementation of a Microtorquemeter==
https://ceur-ws.org/Vol-1730/p03.pdf
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.
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