1. Measurement Systems and Applications
Mariolino De Cecco
Antonio Selmo
Michele Confalonieri

2. Force Panel
Dopo una breve introduzione …
The instrument employed 2

3. [development of serious games with processing]
How its electronics work?
[Antonio Selmo]
Design and purpose of the FP
[a couple of frontal lessons]
Measurements for Diagnostics
[study and identification of the HTF]
Dopo una breve introduzione …
Rehabilitation and its quantification (measure of indexes of performance)
[development of serious games with processing]
Principles of human diagnosis and rehabilitation
[doct Guandalini and Tomasi]
Achronims:
Fprce Panel – FP
Human Transfer Function - HTF
Logic of the Course 3

4. Organization and final examination
Application: identification of human transfer function for dexterity assessment and serious games for rehabilitation
Course:
frontal lessons (few)
exercitation with matlab
building of the application with Processing
visit to a clinic
Method:
study of touch technology
study of signal analog elaboration and conversion
acquisition of human data
signal processing
Exam:
oral discussion
homework
Material of the course can be found at
Organization and final examination

5. Project acronym: VERITAS
Project number:
Project acronym: VERITAS
Project full title: Virtual and Augmented Environments and Realistic User Interactions To achieve Embedded Accessibility DesignS
Site:
Starting date: 1 January 2010
Duration: 48 Months VERITAS is an Integrated Project (IP) within the 7th Framework Programme, Theme FP7-ICT , Accessible and Assistive ICT
VERITAS Project

6. Design and purpose of the FP - VERITAS Project
Virtual and Augmented Environments and Realistic User Interactions To achieve Embedded Accessibility DesignS
Method
SP1: development of virtual users
SP2: development of the simulation platform
SP3: validation
OBJECTIVE develop virtual humans for accessibility design in virtual simulation of ICT and non ICT products
UNITN activities
Modeling
Measurement
Design and purpose of the FP - VERITAS Project

7. Systems developed: Garment based Motion Capture: Ga-MoCap
Multi-axis load cell
Force Panel
VERITAS Project - measurement systems developed 7

8. Diagnostics by human dexterity estimation Requirements:
Measure position of the touch
Measure the applied force
Store the above for path and trajectories
Accuracy and sampling frequency able to reveal human dexterity
Visual feedback
Idea: “Force Panel”
Display LCD
Touch panel
Force transducers
Punto di partenza del lavoro: volontà di valutare …
In riferimento ad un’immagine, che può rappresentare dei pulsanti, dei percorsi o delle traiettorie, si vogliono misurare la posizione e la forza impressa dal dito, a frequenze e accuratezze tali da poter valutare le abilità umane.
Da qui è nata l’idea di uno strumento dotato di … , denominato poi “Force Panel”
Design and purpose of the FP - requirements 8

9. Stato dell’arte Touch screen LCD and cameras Graph tablets
Tra i sistemi trovati in letteratura sono state analizzate alcune applicazioni che impiegano interfacce grafiche e possibilità di considerare la forza, tra i quali …
Design and purpose of the FP - state of the art 9

10. Stato dell’arte joystick Aptics devices and virtual reality
… nulla di ciò misura contemporaneamente forza e posizione in relazione all’accuratezza del tocco.
Design and purpose of the FP - state of the art 10

11. Force Panel Design and purpose of the FP - Design
Dopo una breve introduzione …
Design and purpose of the FP - Design 11

12. Schema della struttura (disposizione dei vincoli)
Horizontal use
Vertical use
Sensore Composito VS Sensore Monolitico
= perpendicular to LCD
= parallel to LCD
3 load cells
Design and purpose of the FP - Design 12

13. Tipologie di vincolo considerate
Spherical joints
wires
2 solutions !
Design and purpose of the FP - Design 13

14. Design and purpose of the FP - Design

15. Variante con teste a snodo
mechanical design: spherical joint

16. mechanical design: wires
Dopo una breve introduzione …
mechanical design: wires 16

17. mechanical design: wires constraints

18. mechanical design: wires constraints

19. F Requirements: No buckling No finger force through the blues
Diameter 1 mm
Wires with load cell
Length 10 mm (due to physical constraints)
wires
Length 30 mm (FEM analysis → finger force < 0.3 %) F
mechanical design: wires length

20. Lunghezza dei fili mechanical design: wires length horizontal Vertical
Worst case for buckling
Worst case for force leakage
mechanical design: wires length 20

21. Errore lettura forza [%]
Critical length ≈ 65 mm
Force lost:
Moments ≈ 10-3 – 10-6 Nm
Caso
Errore lettura forza [%]
Worst case horizontal, l = 10 mm
2.41
Worst case vertical, l = 10 mm
2.50
Worst case for buckling, l = 10 mm
5.32
Worst case for buckling, l = 20 mm
0.73
Worst case for buckling, l = 30 mm
0.22
Worst case for buckling, l = 30 mm, e = 0.5 mm
0.23
Worst case for buckling, l = 30 mm, e = 1 mm
0.27
mechanical design: wires length 21

22. System design: overall layout
Touch panel
LCD
VGA
Force sensors PC
Force Conditioning
2 x DIGITAL OUT
USB
µController
2 x ANALOG IN
3 x ANALOG IN
System design: overall layout

23. Touch position measurement circuit
A touch screen is a 2-dimensional sensing device constructed of 2 sheets of material separated slightly by spacers
A common construction is a sheet of glass providing a stable bottom layer and a sheet of Polyethylene (PET) as a flexible top layer
The 2 sheets are coated with a resistive substrate, usually a metal compound called Indium Tin Oxide (ITO). The ITO is thinly and uniformly sputtered onto both the glass and the PET layer
Tiny spacers are placed between the 2 sheets in order to prevent false touch
When the PET film is pressed the two resistive surfaces meet. This position can be read as illustrated in next slides
Touch position measurement circuit

24. its electrical conductivity optical transparency
Indium tin oxide (ITO, or tin-doped indium oxide) is a solid solution of indium(III) oxide (In2O3) and tin(IV) oxide (SnO2), typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to grey. In the infrared region of the spectrum it is a metal-like mirror.
Indium tin oxide is one of the most widely used transparent conducting oxides because of its two chief properties:
its electrical conductivity
optical transparency
Touch position measurement circuit

25. Touch position measurement circuit
5 V y+ L
VS - sense
GND
R0 is the total resistance of the substrate
RT is the touch resistance
Touch position measurement circuit

26. Touch position measurement circuit
Reading the x coordinate is similar
Note that in the equivalent circuit there are capacitive effects that lead to a certain delay that usually is less than 10 ms
Touch position measurement circuit

27. Electronics scheme

28. Pre-Amplificazione e Filtro analogico
Alim.
cella
Output
Alim. condiz.
(± 15 V DC)
Circuito di condizionamento
Pre-Amplificazione e Filtro analogico
passa basso
Bessel V ordine
DC / DC
Alimentazione
(12 V DC)
Cella di carico μC
Shift del segnale
(μC legge solo
tensioni positive)
Amplificazione
Conditioning unit

29. Conditioning unit

30. Full Wheatstone bridge
Bessel lowpass 5° order
Gain and offset adjustment: Arduino reads only positive voltages (0 – 5 V)
Conditioning unit

31. Conditioning unit No sovraelongation 50s Tempo di assestamento 500 s
RISPOSTA TEMPORALE AL GRADINO DEL FILTRO PASSA BASSO DEL 5° ORDINE (Risposta di Bessel con frequenza di taglio 1 kHz)
Conditioning unit

32. Attesa assestamento circuito RC (costanti, variabili e pin μC)X Y F1 F2 F3
Alimentazione lungo X
Attesa assestamento circuito RC
Lettura valore X
Alimentazione lungo Y
Lettura valore Y
Lettura valore F1
Lettura valore F2
Lettura valore F3 PC
Inizializzazioni
(costanti, variabili e pin μC)
Arduino UNO
sw design: embedded system

33. Ricezione dati ed applicazione modello di taratura
t [ms]
TASK 1 – Arduino
TASK 2 – PC
TASK 3 – PC
PIN per lettura X
Gestione delle immagini in relazione alle risposte di chi sta di fronte al pannello
t assest. RC 5
Read X
5.1
PIN per lettura Y
Read F1, F2, F3 nel t assest. RC 8
10.1
Read Y
10.2
Invio dati via RS-232
15.2
Ricezione dati ed applicazione modello di taratura
2 task paralleli su PC:
- uno segue l’Arduino, - uno è indipendente
25.2
sw design: task analysis

34. Elaboration and graphical output
Acquisition
Elaboration and graphical output
Inizializzazioni
Lettura RS-232
Riconoscimento stringa
Distinzione segnali
Eventuali operazioni di filtraggio
Operazioni di taratura
Inizializzazioni
Attesa inizio acquisizione
Calcolo della tara del sistema
Elaborazione (gestione delle immagini in relazione all’interazione con l’utente)
sw design: two independent tasks on the PC

35. Touch position (resistive touch) Force (load cell)
Touch position (load cell)
Calibration

36. Force Panel - calibration

37. Linear behaviour on both directions No interactions
Measurement model:
Linear behaviour on both directions
No interactions
uncoupled modelling
xm [pixel]
ym [pixel]
xm = f (xa)
ym = f (ya)
xa [bit]
ya [bit]
calibration: position

38. Non-linear behaviour for:
Touch position
Force
FT [bit]
Fm [N]
Fm[N] = f (Fa , xm , ym)
xm [pixel]
ym [pixel]
Non si leggono bene le scritte sul grafici
calibration: force 38

39. WORK IN CLASS Force Panel - calibration: force
For N measurements made in different positions and with different forces it is possible to build the following linear relation
Than, with a pseudoinverse computation, the 10 coefficients of the polynomial model are estimated
WORK IN CLASS Force Panel - calibration: force

40. WORK IN CLASS Force Panel - calibration: force
The pseudoinverse computation gives the 10 coefficients of the polynomial model:
NOTE: ATA is generally a square and full rank matrix
WORK IN CLASS Force Panel - calibration: force

41. WORK IN CLASS Force Panel - calibration: force
Files given:
read_float.m
How to use read_float :
jj = 1 ; % numero file
file = ['dati_celle_armon_', num2str(jj), '.txt'] ;
dati = read_float(file, ',', ':') ;
clc
Dati = cell2mat(dati);
% grammi -> Newton
Dati(:,1) = Dati(:,1)*(9.81/1000) ;
WORK IN CLASS Force Panel - calibration: force

42. WORK IN CLASS Force Panel - calibration: force
% Data are saved on 9 files “dati_celle_armon_1…9.txt”
As follows on columns:
% 1 -> calibration load [g]
% 2 -> x position [pixel]
% 3 -> y position [pixel]
% 4 -> load cell 1 (in alto) [N]
% 5 -> load cell 2 (in basso a sx) [N]
% 6 -> load cell 1 (in basso a dx) [N]
% 7 -> load cell sum [N]
WORK IN CLASS Force Panel - calibration: force

43. WORK IN CLASS Force Panel - calibration: force
chi2gof Chi-square goodness-of-fit test on the vector e
Performs a chi-square goodness-of-fit test for discrete or continuous distributions. The test is performed by grouping the data into bins, calculating the observed and expected counts for those bins, and computing the chi-square test statistic SUM((O-E).^2./E), where O is the observed counts and E is the expected counts. This test statistic has an approximate chi-square distribution when the counts are large.
WORK IN CLASS Force Panel - calibration: force

44. Analyse the residuals and the validation behaviour
Procedure:
With the pseudoinverse computation estimate the 10 coefficients of the proposed polynomial model taking one data file at your choice
Apply the estimated coefficients to the model to predict (validate) the model behaviour using a different data file
Analyse the residuals and the validation behaviour
Apply the chi2gof test to verify the randomness of the residuals
Try to choose different mathematical models and see how the chi2gof test performs
WORK IN CLASS Force Panel - calibration: force

45. Force Panel – calibration position
F1a [bit]
xm = f (F1a , F2a , F3a)
ym = f (F1a , F2a , F3a)
F2a [bit]
F3a [bit]
xm [pixel]
ym [pixel]
Dire che le formule dei piano appoggiato su 3 punti sballavano nell’intorno dei vincoli planari. 1 2 3
Force Panel – calibration position 45

46. Nail Finger finger horizontal
Resolution
Accuracy
Position X [mm]
< 0.40
± 1.80 (al 95%)
Position Y [mm]
< 0.30
Force [N]
< 0.05
± 0.10 (al 95%)
Time [ms] 10
± 5
Nail Finger finger horizontal
Yellow: resistive touch
Blue: load cell reconstruction
Force Panel – calibration position