Transcript Force Sensitive Resistor

Force Sensitive Resistor
Johnnie Chang
October 19th, 2009
Force Sensitive Resistor（FSR）
FSR is a type of resistor whose resistance changes
when a force or pressure is applied.
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Various Pressure/Force sensing principles
Piezoresistive
Capacitive
Electromagnetic
Piezoelectric
Optical
Potentiometric
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FSR
The FSR is a force sensor that employs the Piezoresistive effect.
The sensitivity of piezoresistive devices is characterized by the gauge factor
(or strain factor):
Where
ε = strain = ΔL / L
ΔR = change in resistance
R = unstrained resistance
α = temperature coefficient
θ = temperature change
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Basic constuction of FSR
A force sensing resistor is mainly made up of two parts.
A resistive material applied to a film
A set of contacts applied to another film
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Principle
The resistive material serves to make an electrical path between
the two sets of conductors on the other film.
Together they fit into a circuit that forms a simple voltage divider
When a force is applied to this sensor, a better connection is made
between the contacts, hence the conductivity is increased.
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Special resistive material
 The resistive material applied to the sensing film
consists of both electrically conducting and nonconducting particles suspended in matrix and are
formulated to reduce the temperature
dependence, improve mechanical properties and
increase surface durability..
 Force applied to the sensing film causes particles
to touch the conducting electrodes, changing the
resistance of the film.
Force vs. Resistance characteristics
The resistance of FCR is inversely proportional to the force applied.
Notice: The threshold, or "break force", that swings the
resistance from greater than 1M to about 50-100 K.
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Force vs Conductance
The area enclosed by two doted curves represents a typical part-topart repeatability envelope. This error band determines the maximum
accuracy of any general force measurement.
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Pro and Con
Pro
1. Small size, very thin, flexible application, low cost
2. Not sensitive to vibration or heat
3. Linear response
4. Detect even very weak forces.
Con
1. not very accurate, only qualitative results are generally obtainable. The
part-to-part repeatability tolerance held during manufacturing ranges from
±15% to ±25% of an established nominal resistance.
Ideal for control applications where accuracy isn’t critical
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Application
Touch sensor in robotics, provide tactile force feedback
for robotic arms to ensure safe, accurate, and
independent handling of products and equipment
In sports, measure the actual grip forces on golf clubs,
tennis racquets, baseball bats, etc. to better analyze the
distinct forces involved, or diagnose a problem
Automotive Occupant
detection
9
Common package and pricing
 Price range from a few dollars to a few tens of
dollars
Reference
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http://en.wikipedia.org/wiki/Force_Sensing_Resistor
http://en.wikipedia.org/wiki/Pressure_sensor
http://www.trossenrobotics.com/c/robot-force-sensor-fsr.aspx
http://en.wikipedia.org/wiki/Piezoresistive
http://soundlab.cs.princeton.edu/learning/tutorials/sensors/node8.html
http://www.interlinkelectronics.com/force_sensors/technologies/fsr.html
http://blog.makezine.com/archive/2009/05/force_sensitive_resistor_fsr_tutori.html
www.themegallery.com