TACTILE SENSORS
LT A C THOMAS
SCOPE
• INTRODUCTION
• RELEVANCE
• TYPES
• MARINE APPLICATIONS
• CONCLUSION
INTRODUCTION
• DEFINITION : TACTILE SENSOR ARE DEVICES
WHICH MEASURES THE PARAMETERS OF A
CONTACT BETWEEN THE SENSOR AND AN
OBJECT.
• THE HUMAN ELEMENT
RELEVANCE
• SINGLE POINT CONTACT
• SENSITIVITY
• SENSOR BAND WIDTH
• LOW HYSTERESIS
• ROBUST
TYPES OF TACTILE SENSORS
• OPTICAL
• PIEZOELECTRIC
• RESISTIVE
• CAPACITIVE
• MAGNETIC
• STRAIN GAUGE
OPTICAL TACTILE SENSORS
OPTICAL FIBRE
BASED SENSOR
• OPTICAL WAVE
GUIDE
• SOFT RUBBER AT
THE SURFACE
• A LIGHT SOURCE
• OPTICAL DETECTOR
OPTICAL TACTILE SENSOR
• PHOTOELASTICITY
• MODULATING THE INTENSITY OF LIGHT BY
MOVING AN OBSTRUCTION INTO THE LIGHT
PATH
OPTICAL TACTILE SENSORS
• TYPES
– INTRINSIC
– EXTRINSIC
• ADVANTAGES
– IMMUNITY TO EXTERNAL ELECTROMAGNETIC
INTERFERENCE
– LOW WEIGHT AND VOLUME
PIEZOELECTRIC SENSORS
PRINCIPLE OF PIEZOELECTRICITY
• CHANGE IN THE PIEZOELECTRIC RESONANCE
FREQUENCY OF THE MATERIAL WITH THE APPLIED
STRESS.
• CHANGES IN ELECTRIC CHARGE
ELECTRIC
PLATES
PIEZO ELECTRIC
CRYSTAL
FORCE or
VIBRATION
V
THE RESONANCE FREQUENCY OF THE RESONATING
MATERIAL :
• T = THICKNESS OF THE PIEZOELECTRIC MATERIAL.
• F0 = NATURAL MECHANICAL RESONANCE
FREQUENCY.
• K = STIFFNESS CONSTANT OF THE MATERIAL.
• P = DENSITY OF THE MATERIAL.
• F = APPLIED FORCE
• ∆f = CHANGE IN FREQUENCY
MATERIALS
POLYVINYLIDENE FLUORIDE (PVDF), QUARTZ, LEAD
ZIRCONATE TITANAATE (PZT)
ADVANTAGE
• GETTING A CONTOUR OF THE OBJECT.
• MEASUREMENT OF PRESSURE
• SIGNAL REGARDING TOUCH AND NO-TOUCH OF
THE OBJECT
RESISTIVE TACTILE SENSORS
BASED ON THE CHANGE OF THE ELECTRICAL
RESISTANCE BETWEEN A CONDUCTIVE
POLYMER AND ATLEAST TWO ELECTRODE
WORKING PRINCIPLE
FIGURE 1
FIGURE 2
SALIENT FEATURES
• A SIMPLE SIGNAL CONDITIONING
ELECTRONICS
• HYPEBOLIC STYLE CHARACTERISTIC BETWEEN
THE LOAD APPLIED AND THE ELECTRICAL
RESISTANCE
• ROBUST DUE TO SIMPLE CONSTRUCTION
CONSTRUCTION
FIGURE 1
FIGURE 2
SENSOR MATERIAL
• EVA FOAM
• SILICON RUBBER
• PTFE
EVA SILICON PTFE
RUBBER
Realizable 150 kPa 100 kPa 2.000 kPa
measurement
range
Temperature -70 to 60 °C -100 to 316 °C -260 to 300 °C
range
Ductility high high low
Polymer type thermoplastic thermoset thermoset
Processing sawing, (jet-) compression (jet-) cutting
cutting, milling molding,
jet cutting injection
molding
CAPACITIVE TACTILE SENSORS
CAPACITIVE SENSORS UTILISE THE CHANGE OF
CAPACITANCE BETWEEN TWO ELECTRODES
COVERING A DEFORMABLE DIELECTRIC.
PRINCIPLE OF WORKING
The basic electrical property of capacitance – a measure of an object’s
ability to store electrical charge –two electrodes with area A separated by
an air gap d as shown. If the air gap decreases, the capacitance C goes
up.
SENSOR TECHNOLOGY COMPARISON
MAGNETIC BASED SENSOR
• TWO APPROACHES
(1) CHANGE OF FLUX DENSITY
-MEASURED USING MAGNETO RESISTIVE DEVICES
(2)CHANGE OF MAGNECTIC COUPLING BETWEEN WINDINGS
-DEFORMATION OF MAGNECTO ELASTIC CORE
MAGNECTIC BASED SENSOR
• ADVANTAGES
– HIGH SENSITIVITY
– DYNAMIC RANGE
– NO MECHANICAL HYSTERESIS
– LINEAR RESPONSE
– ROBUSTNESS
MARINE APPLICATIONS
• Local ice load on ships
– test loads on hull in contact
with ice
– Tested in straight going
and turning modes
– Tested using two models
– Interpreted for the vessel being built
MARINE APPLICATIONS
• Local ice loads on ships
– I-SCAN 210 tectile sensor sheets used
– Sensors located at four positions
– Measures pressure distribution
– Largest loading on bow shoulder
MARINE APPLICATIONS
• Shear and normal force measurements
– Capacitive sensor is used
– Phase and amplitude changes gives forces applied
• Finger tip sensing system in UW Gripper
– Strain gauge sensor used
– Measures force exerted by gripper
