SMART 2004 SMART 2004 A NEW CONTROL SYSTEM FOR A NEW CONTROL SYSTEM FOR FAST MOTION CONTROL OF FAST MOTION CONTROL OF SMA ACTUATOR WIRES SMA ACTUATOR WIRES Yee Harn Teh and Roy Featherstone Yee Harn Teh and Roy Featherstone Department of Information Engineering, Department of Information Engineering, Research School of Information Sciences and Research School of Information Sciences and Engineering, Engineering, The Australian National University. The Australian National University.
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SMART 2004 A NEW CONTROL SYSTEM FOR FAST MOTION CONTROL OF SMA ACTUATOR WIRES Yee Harn Teh and Roy Featherstone Department of Information Engineering,
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SMART 2004SMART 2004
A NEW CONTROL SYSTEM A NEW CONTROL SYSTEM
FOR FAST MOTION CONTROL FOR FAST MOTION CONTROL
OF SMA ACTUATOR WIRESOF SMA ACTUATOR WIRES
Yee Harn Teh and Roy FeatherstoneYee Harn Teh and Roy FeatherstoneDepartment of Information Engineering,Department of Information Engineering,
Research School of Information Sciences and Engineering,Research School of Information Sciences and Engineering,The Australian National University.The Australian National University.
SMART 2004SMART 2004
OutlineOutline
In this talk, we describeIn this talk, we describe
A rapid heating mechanism that doubles the A rapid heating mechanism that doubles the velocity of SMA antagonistic-pair actuatorsvelocity of SMA antagonistic-pair actuators
A simple control system for fast motion control A simple control system for fast motion control with small limit cycleswith small limit cycles
SMART 2004SMART 2004
Long-Term ObjectivesLong-Term Objectives
To achieve fast and accurate position and force To achieve fast and accurate position and force control using SMA actuatorscontrol using SMA actuators
To build and experiment with low-inertia robots To build and experiment with low-inertia robots using SMA actuatorsusing SMA actuators
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So How Fast Are SMA?So How Fast Are SMA?
Hear this: Hear this:
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Rapid Heating MethodRapid Heating Method
Measure the electrical resistance of the SMA Measure the electrical resistance of the SMA wirewire
thenthen limit current to safe (datasheet) valuelimit current to safe (datasheet) value
elseelse allow a larger currentallow a larger current
Note: supplying the SMA wire with currents Note: supplying the SMA wire with currents beyond the data sheet safe level over a certain beyond the data sheet safe level over a certain time period may overheat and damage the SMAtime period may overheat and damage the SMA
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Resistance vs. TemperatureResistance vs. Temperature
electrical resistance
temperature
heatingcooling
threshold resistance
safety margin
Allow larger currents
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Current Limiter MechanismCurrent Limiter MechanismMaximum allowable current is a function of measured Maximum allowable current is a function of measured resistanceresistance
Maximum safe heating current,
Imax(R)
Measured Resistance, R
Isafe
Ihigh
Rthresh Rramp
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Control System ArchitectureControl System Architecture
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
Step Response of Modified Step Response of Modified Proportional Controller (With Load)Proportional Controller (With Load)
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ConclusionConclusion
The rapid heating mechanism substantially The rapid heating mechanism substantially increases the SMA’s speed of response without increases the SMA’s speed of response without changing the cooling regimechanging the cooling regimeMotion accuracy could be achieved using better Motion accuracy could be achieved using better motion controllersmotion controllersA modified proportional controller achieves fast, A modified proportional controller achieves fast, accurate motion control of inertia-loaded accurate motion control of inertia-loaded systems, with greatly reduced limit cyclessystems, with greatly reduced limit cycles
SMART 2004SMART 2004
Future WorkFuture Work
Better position control systems for higher motion Better position control systems for higher motion accuracyaccuracy
New test rig with force sensorsNew test rig with force sensors
Experiment with force control of SMA actuatorsExperiment with force control of SMA actuators