BIOMECHANICS & BIOMEDICAL ENGINEERING LOW COST FORCE SENSOR Team members: Gartzonikas Dimitrios Tzortzopoulos Georgios Mentor: Gκousioudi Anastasia - Consultant: Tzeranis Dimitrios

Why. simultaneous force measurements on multiple samples What Why? simultaneous force measurements on multiple samples What? analog input into digital output How? load change resisntance change voltage change

Force sensor assembly main parts Voltage supplies, reference, regulators Force Sensor FSR400 Operational amplifiers Analog to digital converter Cables, resistances, capacitors etc.

Challenges Operational limitations of converter Voltage supply for opamp FSR response affected by: - operational force range - deformation - load distribution on active tip Output signal processing

Practical solutions Simulations (Tina-Ti, LT Spice) Stable connections and mounting Active surface in a rubber sandwich Secondary opamp supply circuit Controllable gain Arduino instead of adc

Defining the FSR’s response… Theory & practice (1) Defining the FSR’s response…

manufacturer vs. experiment… Theory & practice (2) manufacturer vs. experiment…

Final design & implementation

Implementation in detail Ground Negative Voltage FSR Input Positive Voltage Output to converter

Experiment layout

Equipment & protocols Equipment: Experiment conditions: Digital polymeter velocity 0,05 mm/sec Bose test instrument 0,5 Ν force step Arduino Mega steady load for 30 sec Laptop 0,1 – 7,5 N load range rubber discs Φ6x3mm 9 repetitions

Assembly response 7,5 N 7,0 N 6,5 N 6,0 N 5,5 N 5,0 N 4,5 N 4,0 N

Assembly calibration Force Voltage N V ± 0.02 1.5 0.12 2.0 0.23 2.5 0.36 3.0 0.46 3.5 0.58 4.0 0.69 4.5 0.79 5.0 0.86 5.5 0.92 6.0 0.99 6.5 1.05 7.0 1.12 7.5 1.15

Conclusions Reliable response range: 1,5 - 7,5 N F = 2.8677*V^2 + 1.871*V + 1.377 [+/- 0,4 N] Repeatability of results Almost constant deviation for different forces Small contribution of circuit dynamics Limited precision Great circuit robustness & negligible noise

Next steps… Stable multiple mounting Circuit “clean up” for minimal space demands Force offset layout Sample placement with even distribution on FSR surface Arduino code for quicker sampling response Influence of rubber elasticity on the results

Application & future use Part of laboratory equipment for evaluating mechanical properties of cartilage samples

Feel free to ask us any questions… THE END We would like to thank our mentor and consultant for their support and guidance Feel free to ask us any questions…

experiment measurements … Back up slides (1) experiment measurements … step test 1 test 2 test 3 test 4 test 5 test 6 test 7 test 8 test 9 Average ST. DEV. ΑΑ N V 1 0,1 2 0,5 3 1,0 4 1,5 0,146628 0,073314 0,12219 0,097752 0,12228 0,024234 5 0,058651 0,102639 0,136852 6 0,14174 0,063539 0,107527 0,127077 7 8 9 0,112414 10 2,0 0,210166 0,166178 0,219941 0,200391 0,226096 0,021042 11 0,185728 0,234604 12 0,195503 0,229717 13 0,244379 0,215054 14 0,249267 15 0,254154 0,190616 0,239492 16 2,5 0,361681 0,293255 0,312805 0,322581 0,356341 0,020655 17 0,371457 0,327468 0,317693 0,337243 18 0,347019 0,351906 19 0,332356 0,376344 20 0,342131 21 0,356794 22 3,0 0,469208 0,40567 0,464321 0,483871 0,464954 0,013395 23 0,42522 0,474096 24 0,459433 0,449658 0,488759 25 0,439883 0,454545 26 0,493646 27 0,44477

Gain selection diagrams Back up slides (2) Gain selection diagrams