Transcript Slide 1

A NEW CONTROL SYSTEM
FOR FAST MOTION CONTROL
OF SMA ACTUATOR WIRES
Yee Harn Teh and Roy Featherstone
Department of Information Engineering,
Research School of Information Sciences and Engineering,
The Australian National University.
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Outline
In this talk, we describe
A rapid heating mechanism that doubles the
velocity of SMA antagonistic-pair actuators
A simple control system for fast motion control
with small limit cycles
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Long-Term Objectives
To achieve fast and accurate position and force
control using SMA actuators
To build and experiment with low-inertia robots
using SMA actuators
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So How Fast Are SMA?
Hear this:
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Rapid Heating Method
Measure the electrical resistance of the SMA
wire
Algorithm:
If resistance < threshold
then limit current to safe (datasheet) value
else allow a larger current
Note: supplying the SMA wire with currents
beyond the data sheet safe level over a certain
time period may overheat and damage the SMA
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Resistance vs. Temperature
electrical
resistance
cooling
heating
Allow
larger
currents
threshold
resistance
safety
margin
temperature
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Current Limiter Mechanism
Maximum allowable current is a function of measured
resistance
Ihigh
Maximum safe
heating current,
Imax(R)
Isafe
Rthresh
Rramp
Measured Resistance, R
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Control System Architecture
Actual
position
Desired
position
Motion
Sensors
Motion
Controller
Id
Current
Limiter
Ih
Current
Regulator
SMA
element
Measured resistance
Id, desired heating current, is a function of position error. It
does not factor in the state of the SMA element.
Ih, actual heating current, is the minimum of
– Imax(R), the max. safe heating current of the rapid
heating mechanism
– Id from the motion controller
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Experimental Setup
dSPACE
PC
DS1104
ADC
sensed
SMA
voltage &
current
DAC
Enc
encoder
signals
current
commands
Current
Regulators
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Grant’s Two-Stage Relay Controller
Heating
Power
Reverse Actuator
Forward Actuator
Position Error
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Tracking Response of Two-Stage
Relay Controller (No Load)
OFF
Rapid Heating:
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ON
Actual Power to Each Actuator
Rapid Heating:
OFF
ON
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Step Response of Two-Stage Relay
Controller (With Load)
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Modified Proportional Controller
Heating
Power
Reverse Actuator
Forward Actuator
Position Error
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Step Response of Modified
Proportional Controller (With Load)
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Conclusion
The rapid heating mechanism substantially
increases the SMA’s speed of response without
changing the cooling regime
Motion accuracy could be achieved using better
motion controllers
A modified proportional controller achieves fast,
accurate motion control of inertia-loaded
systems, with greatly reduced limit cycles
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Future Work
Better position control systems for higher motion
accuracy
New test rig with force sensors
Experiment with force control of SMA actuators
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Questions
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