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. 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