Download Slides - Roy Featherstone

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.
SMART 2004
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
SMART 2004
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
SMART 2004
So How Fast Are SMA?
Hear this:
SMART 2004
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
SMART 2004
Resistance vs. Temperature
electrical
resistance
cooling
heating
Allow
larger
currents
threshold
resistance
safety
margin
temperature
SMART 2004
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
SMART 2004
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
SMART 2004
Experimental Setup
dSPACE
PC
DS1104
ADC
sensed
SMA
voltage &
current
DAC
Enc
encoder
signals
current
commands
Current
Regulators
SMART 2004
Grant’s Two-Stage Relay Controller
Heating
Power
Reverse Actuator
Forward Actuator
Position Error
SMART 2004
Tracking Response of Two-Stage
Relay Controller (No Load)
OFF
Rapid Heating:
SMART 2004
ON
Actual Power to Each Actuator
Rapid Heating:
OFF
ON
SMART 2004
Step Response of Two-Stage Relay
Controller (With Load)
SMART 2004
Modified Proportional Controller
Heating
Power
Reverse Actuator
Forward Actuator
Position Error
SMART 2004
Step Response of Modified
Proportional Controller (With Load)
SMART 2004
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
SMART 2004
Future Work
Better position control systems for higher motion
accuracy
New test rig with force sensors
Experiment with force control of SMA actuators
SMART 2004
Questions
SMART 2004