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A New Control System for Fast Motion Control of SMA Actuator Wires

This presentation discusses a rapid heating mechanism that increases the velocity of SMA antagonistic-pair actuators, along with a simple control system for fast motion control with small limit cycles. The goal is to achieve fast and accurate position and force control using SMA actuators, and to build and experiment with low-inertia robots using SMA actuators.

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A New Control System for Fast Motion Control of SMA Actuator Wires

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  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

  2. 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

  3. To achieve fast and accurate position and force control using SMA actuators To build and experiment with low-inertia robots using SMA actuators Long-Term Objectives SMART 2004

  4. So How Fast Are SMA? Hear this: SMART 2004

  5. Rapid Heating Method • Measure the electrical resistance of the SMA wire • Algorithm: If resistance < threshold thenlimit current to safe (datasheet) value elseallow 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

  6. Allow larger currents threshold resistance safety margin Resistance vs. Temperature electrical resistance heating cooling temperature SMART 2004

  7. 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

  8. Control System Architecture Motion Sensors • 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 Actual position Id Ih Motion Controller Current Limiter Current Regulator SMA element Desired position Measured resistance SMART 2004

  9. dSPACE DS1104 PC ADC DAC Enc encoder signals sensed SMA voltage & current current commands Current Regulators Experimental Setup SMART 2004

  10. Grant’s Two-Stage Relay Controller Heating Power Reverse Actuator Forward Actuator Position Error SMART 2004

  11. Tracking Response of Two-Stage Relay Controller (No Load) Rapid Heating: OFF ON SMART 2004

  12. Actual Power to Each Actuator Rapid Heating: OFF ON SMART 2004

  13. Step Response of Two-Stage Relay Controller (With Load) SMART 2004

  14. Modified Proportional Controller Heating Power Reverse Actuator Forward Actuator Position Error SMART 2004

  15. Step Response of Modified Proportional Controller (With Load) SMART 2004

  16. 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

  17. 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

  18. Questions SMART 2004

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