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Overview of Embedded Systems Motors and Actuators

This article provides an overview of different types of motors and actuators used in embedded systems, including hydraulic, pneumatic, and electric systems. It covers various types of motors such as stepper motors and permanent magnet DC motors, as well as artificial muscles and shape memory alloys. The article also explores the thermodynamic and packaging issues related to these devices. Additionally, it discusses new technologies in artificial muscles, including chemical polymers and biological muscle proteins.

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Overview of Embedded Systems Motors and Actuators

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  1. Embedded SystemsMotors

  2. Actuators …physical devices that transform electrical, chemical, or thermal energy into mechanical energy… • hydraulic • pneumatic • electric • stepper • permanent magnet DC • artificial muscles • shape memory alloys • polymers • biological • bucky tubes

  3. Hydraulic • 1000-3000 psi • open-loop control • 5KHz bandwidth • great power-to-weight • messy/high maintenance

  4. Hydraulic GRLA - Gorilla (SARCOS) • 1.75 meters from shoulder to wrist • 3000 psi hydraulic • exoskeletal master

  5. Hydraulic - Jumping Spiders • spiders cannot extend their legs by activating muscles alone --- they generally have less developed extensor musculature • blood acts as hydraulic fluid---BP is very high compared to other insects and animals • special valves and muscles compress their forebodies and act as hydraulic actuators for their legs.

  6. Pneumatic • pneuma 300 BC - animal spirits • 60-100 psi • jet-pipe servo valves • passively backdrivable • delicate

  7. Pneumatic - McKibben Air Muscles • stroke about 40% of free length • 0-60 psi • power-to-weight up to 100:1 • backdrivable • easily packaged • relatively slow

  8. Electric Motors - Stepper • precise open-loop • low torque • resonance (50-150 steps/sec) • cogging

  9. Electric Motors - Permanent Magnet DC Lorentz force • back emf • commutation

  10. Electric Motors - Commutation

  11. Electric Motors - Permanent Magnet DC • cheap reliable • cogging • big torques • good power-to-weight • continuous operation • high speeds iron core surface wound moving coil

  12. Electric Motors - Gearboxes Inertia of load can be dominated by the inertia of the rotor

  13. Interfacing Electric Motors • reversing polarity • terminals floating - freewheel • terminals shorted - brake • switches are opened and closed at different rates and durations to supply different RMS voltages - pulse width modulation (PWM)

  14. Interfacing Electric Motors void fd(int m) void bk(int m) void off(int m) void ao() void motor(int m, int p)

  15. Artificial Muscles Mechanical properties: elastic modulus, tensile strength, stress-strain, fatigue life, thermal and electrical conductivity Thermodynamic issues: efficiency, power and force density, power limits Packaging: power supply/delivery, device construction, manufacturing, control, integration

  16. Artificial Muscles - Shape Memory Alloys • Nickel Titanium - Nitinol • Crystalographic phase transformation from Martesite to Austenite • Contract (when heated) 5-7% of length - 100 times greater effect than thermal expansion • Relatively high forces • About 1 Hz

  17. Artificial Muscles - New Technologies • Chemical polymers - gels (Jello, vitreous humor) • 1000 fold volume change ~ temp, pH, electric fields • force up to 100 N/cm2 • 25 um fibers -> 1 Hz, 1 cm fiber -> 1 cycle/2.5 days • Electroactive polymers • store electrons in large molecules • change length of chemical bonds - batteries/capacitors • deform ~ V2

  18. Artificial Muscles - New Technologies • Biological Muscle Proteins • actin and myosin • 0.001 mm/sec in a petri dish • Fullerenes and Nanotubes • graphitic carbon • high elastic modulus -> large displacements, large forces • macro-, micro-, and nano-scale • extremely robust • potentially superior to bioligcal muscle

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