ACTUATOR SUMMARY

ACTUATOR SUMMARY

 

Actuators Advatages Disadvantages Comments
Mammalian Skeletal Muscle
  • Large strains (20%)
  • Moderate stress (350 kPa blocking)
  • Variable stiffness
  • High energy fuel (20-40 MJ/kg)
  • Efficient (~40%)
  • Good work density (<40 kJ/kg)
  • High cycle life (by regeneration)
  • Not yet engineering material
  • Narrow temperature range of operation
  • No catch state (expends energy to maintain force w/o moving unlike mollusk muscle)
  • Incredibly elegant mechanism that is a challenge to emulate. Muscle is a 3D nanofabricated system with integrated sensors, energy delivery, waste/heat removal, local energy supply, and repair mechanisms.
Dielectric Elastomers
  • Large strains (20% – 380%)
  • Moderate stress (several MPa peak)
  • Large work density (10k to 3.4MJ/m3)
  • Moderate to high bandwidth (10 Hz to > 1kHz)
  • Low cost
  • Low current
  • Good electromechanical coupling & efficiency (>15% typical, 90% max)
  • High voltages (> 1kV) and fields (~150 MV/m)
  • Typically requireds DC-DC converters
  • Compliant (E ~ 1MPa)
  • Pre-stretching mechanisms currently add substantial mass and volume, reducing actual work density and stress
  • Potential to lower fields using high dielectric materials
  • Small devices are favored for high frequency operations eg. MEMS (due to the more efficient heat transfer which prevents thermal degradation, and the higher resonant frequencies)
  • Starting materials are readily available
Relaxor Ferroelectric Polymers
  • Moderate strain (<7%)
  • High stress (45 MPa blocking)
  • Very high work density (up to 1MJ/m3 internal strain)
  • Stiff (400 MPa)
  • Strong coupling (0.4) & efficiency
  • Low current
  • High voltages (> 1kV) and fields (~150 MV/m)
  • Typically requireds DC-DC converters
  • Synthesis of typical materials involves environmentally regulated substances
  • Cycle life is unclear & may be limited by electrode fatigue and dissipation
  • Limited temperature range
  • Lower voltages and fields are being achieved using new high dielectric composites.
  • Small devices are favored for high frequency operations eg. MEMS
  • Unique combinations of high stiffness, moderate strain & reasonable efficiency
Liquid Crystal Elastomers
  • Large strains in thermally induced materials (45%)
  • Moderate strains in field induced materials (2-4%)
  • High coupling (75%) in electric materials
  • Subject to creep
  • Thermal versions are slow unless very thing or photoactivated
  • High fields (1-25MV/m)
  • Low efficiency in thermal materials
  • New material with much promise and much characterization to be done. Photo-activation has been achieved.
Conducting Polymers
  • High stress (34 MPa max, 5MPa typical)
  • Moderate strains (~2%)
  • Low voltage (~2V)
  • High work density (100kJ/m3)
  • Stiff polymers (~1GPa)
  • Low electromechanical coupling
  • Currently slow (several hertz maximum to obtain full strain)
  • Typically needs encapsulation
  • Promising for low voltage applications. Speed and power will improve dramically at small scales.
Molecular Actuators
  • Large strain (20%)
  • Moderate to high stress (>1MPa)
  • Low voltage (2V)
  • High work density (>100kJ/m3)
  • Currently slow
  • Needs encapsulation
  • Great promise of overcoming may of the shortcomings of conducting polymer actuators, but still very early in development
Carbon Nanotubes
  • High stress (>1MPa)
  • Low voltage (2V)
  • Very large operating temperatures
  • Small strain (0.2%)
  • Currently has low coupling
  • Materials are presently expensive
  • Great potential as bulk materials approach properties of individual nanotubes
Ionic Polymer Metal Composite (IPMC)
  • Low voltage (<10V)
  • Large displacement (mechanical amplification built into the structure)
  • Low coupling and efficiency
  • Usually no catch state (consumes energy in holding position)
  • Requires encapsulation
  • IPMC driven toys and demonstration kits available
Thermally Activated Shape Memory Alloy
  • Very high stress (200 MPa)
  • Unmatched specific power (> 100kW/kg)
  • Moderate to large strain (1-8%)
  • Low voltage (actual voltage depends on wiring)
  • Great work density (>1MJ/m3)
  • Difficult to control (usually run between fully contracted and fully extended but not between)
  • Large current and low efficiencies (<5%)
  • Cycle life is very short at large stess amplitudes
  • Readily available. Geerally thought of as slow, but can achieve millisecond response times using short high current pulses and water cooling
Ferromagnetic Shape Memory Alloys
  • High stress (<9 MPa)
  • High frequency (>100Hz)
  • Moderate strain (up to 10%)
  • High coupling (75%)
  • Bulky magnets are required which greatly reduce the work density
  • Costly single crystal materials
  • Operates in compression and thus needs a restoring force
  • Displacement is typically all or nothing, as intermediate states are difficult to reach reproducibly
  • Commercially available

This material is based on Artificial Muscle Technology: Physical Principles and Naval Prospects by John D. Madden, Nathan Vandesteeg, Patrick A. Anquetil, Peter G. Madden, Arash Takshi, Rachel Z. Pytel, Serge R. Lafontaine, Paul A. Wieringa and Ian W. Hunter in the IEEE Journal of Oceanic Engineering, Vol. 29, No. 3, p. 706, July 2004.
©John Madden, 2005