ScienceDirect. Resistive-based Sensor System for Prosthetic Fingers Application

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1 Available online at ScienceDirect Procedia Computer Science 76 (2015 ) IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015) Resistive-based Sensor System for Prosthetic Fingers Application Nur Aqilah Zainuddin a, Nur Farahin Anuar a, Ahmad Luqman Mansur a, Nur Izzati Mohd Fauzi a, Wan Fazlida Hanim a, and Sukreen Hana Herman a,b, * a Faculty of Electrical Engineering, Universiti Teknologi MARA Shah Alam, Shah Alam, Selangor b CoRe of Frontier Materials & Industry Applications, Universiti Teknologi MARA Shah Alam, Selangor Abstract Amputees seldom experience from physical difficulties due to their incapability to use their extremities. To aid the amputees in acquiring an operative replacement fingers at a feasible cost, a 3D printed prosthetic fingers model interfaced with Readout Interfacing Circuit (ROIC) and a microcontroller is presented. A resistive-voltage as well as sensitive active bridge circuit for ROIC has been proposed for measuring very small resistance changes of a tactile sensor attributable to vary the gestures of the prosthetic fingers. To allow more than one prosthetic fingers motion, two servo motors are embedded which offers two choices of gestures depending on the resistance of the tactile sensor. An experimental result of ROIC has been compared with conventional bridge circuit. The result reveals that the active bridge circuit is more sensitive than conventional full bridge circuit The Authors. Published by Elsevier by Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of organizing committee of the 2015 IEEE International Symposium on Robotics and Intelligent Peer-review under responsibility of organizing committee of the 2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015). Sensors (IRIS 2015) Keywords:3D printed prosthetic fingers, Readout Interfacing Circuit; Resistive-based Sensor 1. Introduction Those who lose a limb or two are categorized as amputees, and they perform daily routines in different ways that normal people do. Therefore people have been developing prosthetics or artificial limbs, a substitute for a * Corresponding author. Tel.: address: hana1617@salam.uitm.edu.my The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of organizing committee of the 2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015) doi: /j.procs

2 324 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) missing or defective part of the body. Prosthetics dated back even to Egyptian periods 1. Since then prosthetics have come a long way. Although there have new technologies and breakthroughs to help drive the field of prosthetics further, cost becomes an issue. Recently, there have been many efforts to produce functioning and affordable prosthetic fingers 2,3,4. This is further supported by the prevalence of 3D Printers. These are obviously cheaper than the ones made of advanced plastic and carbon fibres. Tactile sensors and artificial limbs comes hand-in-hand with one another. Tactile sensing has been developed in the past in robotic applications 5,6. Though robots are not yet able to copy the way biological systems extract tactile information do, it still provides researchers a concept to work on 7. Despite the increase in development and research of tactile and haptic sensing, usage of tactile sensing in the robotics is still quite low due to no actual market drive 8. Based on 9, there are three major classes that can measure principle of the tactile sensor cells which are optical, capacitive and resistive sensor. Besides that, a voltage-mode Wheatstone bridge was employed for firstly interfacing resistive sensors in an analogue system. It is used to compare the signal to some set point value. The conventional Wheatstone bridge as the main topologies for resistive sensors offers an attractive choice for measuring small resistance and it is widely used 10,11. A. De Marcellis et al 12 presented a new approach based on current signals, suitable for the detection of very low variations of resistive sensors in a Wheatstone bridge configuration. Additionally, T Islam et al 10,13 presented a sensitive detection electronics for measurement of incremental resistance with high degree of accuracy employing an active bridge circuit whose output is almost four times than a conventional bridge circuit. It is therefore, the conventional Wheatstone s bridge has been modified using active devices for enhancement of sensitivity 13, which is also the active bridge circuit as the ROIC presented in this paper. This paper presents the prove of concept of a system that consists of an ROIC, a microcontroller and a tactile sensor applied to a 3D prosthetic fingers to exhibit more than one gestures depending on the input from the tactile sensor. 2. Design Methodology 2.1. System Setup The resistive sensor based prosthetic fingers system is constructed from four building blocks; the sensor, ROIC including the low pass filter, microcontroller and 3D printed prosthetic fingers as shown in the block diagram in Fig. 1 below. The resistance changes of the tactile sensor are detected and converted by the ROIC and will be fed to the microcontroller to produce output of the system that is the finger movement. The interfacing circuit uses the inverting operational amplifier and Wheatstone bridge as the core. Hence, it will extract different output voltages depending on the resistivity changes on the tactile sensor. As an observation, the extracted voltage is then fed to the microcontroller which lets two different gestures of the prosthetic fingers to prove the functionality of the tactile sensor system Tactile Sensor Figure 1. System Block Diagram The tactile sensor is made of Indium Tin Oxide (ITO) coated Polyethylene terephthalate (PET) flexible substrate connected to copper wires. ITO is a conductive material and the deformation of ITO will influence its resistance that will be extracted by the ROIC and converted into voltage before being fed into the microcontroller. The schematic diagram of the sensor is shown in Fig. 2.

Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) 323 329 325 2.3. Readout Interfacing Circuit Figure 2.

3 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) Readout Interfacing Circuit Figure 2. Schematic diagram of the sensor (a) top view and (b) side view The conventional Wheatstone bridge, shown in Fig. 3(a), is widely used as its technique offers an attractive alternative for measuring small resistance. It is a commonly used bridge configuration suitable for sensor applications, which relate the bridge resistance values to the bridge output voltage. In this configuration, VIN is the excitation voltage; R is the value of the fixed bridge resistor and the variable resistor, {R}, where the element varying bridge produces the change in voltage output. (a) (b) Figure 3. Circuit diagram of (a) conventional Wheatstone bridge and (b) the proposed ROIC Major problem encountered in this bridge circuit is low sensitivity due to the large excitation voltage for sufficient full-scale output voltage. This leads in power dissipation and the possibility of error due to sensor selfheating 10. Thus an ROIC based on the Wheatstone bridge with modification using operational amplifier to increase the sensitivity of the conventional bridge circuit has been proposed as shown in Fig 3(b). It is for measuring any incremental resistance change of resistive sensor, {R}. In this work, the sensitivity of the sensor using conventional Wheatstone bridge and active bridge is compared. The ROIC is a linear and sensitive active bridge circuit requiring only few components for its hardware implementation. It has been proposed for measuring very small resistance change due to change in physical quantity 10. This circuit consists of an active bridge circuit with the combination of an inverting adder. Only one element varying bridge configuration is used, which is one sensor is connected across the one of four arms of the bridge, where it is placed on the adjacent sides of the bridge. A buffer is employed in the arm AB to provide isolation from the adjacent arm AC 10. This ROIC is designed in such a way to increase the sensitivity of the conventional bridge circuit in measuring incremental resistance change of resistive sensor, where variation in resistive value due to physical deformation of the sensor is very small

326 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) 323 329 2.4. Noise reduction Figure 4.

4 326 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) Noise reduction Figure 4. Low Pass Filter Circuit Several unwanted frequencies of an electrical signal at the end of the output need to be filtered in reducing the circuit s noise. Hence, low pass filter is introduced and interfaced at the end output of ROIC. This filter is generally constructed using simple resistor-capacitor networks by connecting together in series a single resistor with a single capacitor as in above Fig. 4. The selected cut-off frequency is 1.25 khz and capacitor chosen value is 0.1uF, hence, the resistance is 1.3 kω, calculated using the equation (1) below; (1) Where C is capacitor with the value of 0.1 μf and the F is the cut-off frequency with the value of 1.25 khz Microcontroller and prosthetic fingers The output of the ROIC, after being filtered by the low pass filter is fed into an Atmel microcontroller 1016ATMEGA328P-PU to decide the gestures of the prosthetic fingers depending on the sensor resistance value due to its deformation. The complete system is shown in Fig Results and Discussions 3.1. Sensor testing with ROIC Figure 5. Prosthetic Fingers System Demo To test the ability of the ROIC in capturing the resistance changes of the sensor, the sensor was connected to the ROIC and the ROIC output was measured by a multimeter. The proposed bridge circuit is constructed with an opamp LM324N operating from a single supply over a wide range of voltages and provides a low supply current drain and is independent of the magnitude of the supply voltage. The experiments have been performed using both with upwards and downwards deformation of the sensor and the averaged voltage outputs are plotted with the variation of applied resistance of the sensor.

Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) 323 329 327 TABLE I.

5 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) TABLE I. BENDING OF TACTILE SENSOR AND ITS VOLTAGE OUTPUT From Table I, it is confirmed that the deformation of the sensor results in variation of resistance and the ROIC was able to extract the resistance variation and converted to voltage. The sensitivity of the sensor was calculated by plotting the measurement values of resistance and output voltage and extracting the slope, as shown in Fig. 6. It can be seen that the sensitivity of the upward bending of the sensor is larger than the downward bending. We assume that this is due to the deformation of the effective area of the conductive ITO in which the physical bendings of the sensor, either will apply compressive or tensile force to the ITO and thus giving different resistance and sensitivity of the sensor. Figure 6. Output voltage dependence on sensor resistance for (a) upwards and (b) downwards bending

6 328 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) Figure 7. Output comparison between Wheatstone bridge and ROIC The output of the sensor extracted by the conventional Wheatstone bridge and our ROIC was compared and plotted in Fig. 7. The sensitivity for the conventional Wheatstone bridge was 33.2 mv/cm and that of the ROIC was 45.5 mv/cm, which verified that the proposed ROIC gave higher sensitivity.

Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) 323 329 329 3.2. System Output TABLE II.

movement as shown in the figures of Table II. Therefore, this verified that ROIC was working well and also proved the application of the circuit and ITO/PET as a sensor candidate. 4.

ROIC in terms of its sensitivity has been compared with conventional bridge circuit s sensitivity and it can be deduced that the active bridge circuit is more sensitive than conventional full bridge

7 Nur Aqilah Zainuddin et al. / Procedia Computer Science 76 ( 2015 ) System Output TABLE II. TYPES OF MOVEMENT OF 3D PRINTED PROSTHETIC FINGERS State of Tactile Sensor Gesture The movement of the 3D printed prosthetic fingers were the output of the system and it serves two types of finger movement as shown in the figures of Table II. Therefore, this verified that ROIC was working well and also proved the application of the circuit and ITO/PET as a sensor candidate. 4. Conclusion We have successfully proved the functionality of an active bridge circuit as the ROIC for a tactile sensor that can be applied to a prosthetic fingers system. ROIC in terms of its sensitivity has been compared with conventional bridge circuit s sensitivity and it can be deduced that the active bridge circuit is more sensitive than conventional full bridge circuit. The experimental result also proved that ITO/PET was able to act as a tactile sensor as well as ROIC was functional due to its capability at sensing the resistance changes. Acknowledgment This work is partially supported by Niche Research Grant Scheme (NRGS) (Project code: 600-RMI/NRGS 5/3 (7/2013)). The authors acknowledge the contributions from MyVistaSdn. Bhd. and RMC UiTM. References 1. A. J. Thurston. Pare and Prosthetics: The Early History of Artificial Limbs. ANZ Journal of Surgery 2007;77: B. Bearss, Humanoid Robot Sub-Systems-Five-Fingered Hand, EECS, C. Antfolk, M. D'Alonzo, B. Rosén, G. Lundborg, F. Sebelius, and C. Cipriani. Sensory Feedback in Upper Limb Prosthetics. Expert Review of Medical Devices 2013;10: P.M. Pilarski, M.R. Dawson, T. Degris, J.P. Carey, K.M. Chan, J.S.Hebert, & R. S. Sutton, Adaptive Artificial Limbs: A Real-Time Approach to Prediction and Anticipation, in Robotics & Automation Magazine, IEEE, 2013;20: G. De Maria, C. Natale, S. Pirozzi. Force/Tactile Sensor for Robotic Applications. Sensors and Actuators A: Physical 2012;175: H. Yousef, M. Boukallela, K. Althoeferb. Tactile Sensing For Dexterous In-Hand Manipulation in Robotics A Review. Sensors and Actuators A: Physical 2011;167: R. S. Dahiya, G. Metta, M. Valle, G. Sandini. Tactile Sensing From Humans to Humanoids. Robotics, IEEE Transactions on 2010;26: P.S. Girãoa, P.M.P Ramosa, O. Postolacheb, J.M.D. Pereirab. Tactile Sensors For Robotic Applications. Measurement 2013;46: K. Weiß and H. Wörn.The Working Principle of Resistive Tactile Sensor Cells. Proceedings of the IEEE International Conference on Mechatronics & Automation 2005; T. Islam, F. A. Siddiqui, S. A. Khan, and S. S. Islam. A Sensitive Detection Electronics for Resistive Sensor. 3rd International Conference on Sensing Technology 2008; G. Ferri, P. De Laurentiis, I. Elettrica, F. Ingegneria, and U. L. Aquila. A Low-Voltage Cmos Phase Shifter as A Resistive Sensor Transducer. IEEE International Symposium on Circuits and Systems 2000; A. De Marcellis, C. Reig, and M.-D. Cubells. A Novel Current-Based Approach for Very Low Variation Detection of Resistive Sensors in Wheatstone Bridge Configuration. SENSORS, 2014 IEE.2014; S. Ghosh, A. Mukherjee, K. Sahoo, S. K. Sen, A. Sarkar. A Novel Sensitivity Enhancement Technique Employing Wheatstone s Bridge for Strain and Temperature Measurement. Computer, Communication, Control and Information Technology, 2015 Third International Conference on., 20015;1-6.

Available online at ScienceDirect. Procedia Computer Science 76 (2015 )

Available online at ScienceDirect. Procedia Computer Science 76 (2015 ) Available online at www.sciencedirect.com ScienceDirect Procedia Computer Science 76 (2015 ) 474 479 2015 IEEE International Symposium on Robotics and Intelligent Sensors (IRIS 2015) Sensor Based Mobile