Microactuators. G.K. Ananthasuresh Professor, Mechanical Engineering Indian Institute of Science Bangalore, , India

Transcription

1 Microactuators G.K. Ananthasuresh Professor, Mechanical Engineering Indian Institute of Science Bangalore, , India

2 What are actuators? Actuators use input energy and release output energy in a controlled manner. Mechanical actuators act upon something and move it with force or torque. There are many types of actuators. Based on the type of output energy released Based on the way output energy is released Based on the input energy used

3 Actuators are transducers. Transducers covert one form of energy to another form. Input energy Actuator Output energy Mechanical Optical Radiation Acoustic Fields

4 Actuators with different output energies Mechanical actuators Produce motion Motors, engines, pumps Acoustic actuators Produce sound Optical actuators Produce light LEDs, solid state lasers Others Radiation Fields

5 An actuator s output is usually mechanical. Actuators usually covert input energy into controlled mechanical energy. Input energy Mechanical actuators Output energy Motion Force/torque Resonance Oscillations Deformations etc.

6 Microactuators Produce motions over small distances. Of the order of microns to mm. Produce small forces. Of the order of pn to mn. Produce motion and force in entities of small sizes.

7 Microactuator universe: displacements Bell et al., 2005 J. Micromechanics and Microengineering Displacement resolution Maximum displacement

8 Microactuator universe: forces Bell et al., 2005 J. Micromechanics and Microengineering Maximum force Maximum displacement

9 Biological microactuators: displacements Vliet et al., 2003 Acta Materialia.

10 Biological actuators: forces Vliet et al., 2003 Acta Materialia.

11 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

12 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

13 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

14 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

15 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

16 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological A normally open valve;

17 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

18 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological

19 Mechanical micro actuators with different input energies and how they are used. Electrostatic Electro magnet based Thermal Chemical Piezo electric Shape memory alloy (SMA) Smart material based Light induced Biological Tan et al. (2003)

20 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The maximum displacement possible with an actuator.

21 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth Maximum force/torque generated by an actuator.

22 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The rate at which the generated force/torque decreases with stroke.

23 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The energy (e.g., voltage current) given to the actuator.

24 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The ration of the released energy to the input energy.

25 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The extent to which the force and stroke are linear. Ideally, we want constant force.

26 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The difference in displacement/force for the same values of input energy in up and down strokes.

27 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The time taken for the actuator to respond from the instant the input signal is given.

28 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The unintended shift in force or displacement even when the input energy is steady.

29 Characteristics of a mechanical (micro)actuator Stroke Force/torque Stiffness Input energy Efficiency Linearity Hysteresis Response time Drift Bandwidth The frequencies at which the actuator can reliably provide the rated displacement and force.

30 Some microactuators Electrostatic micromotors Electrostatic comb drive Magnetic actuators Thermal microactuators Pneumatic actuators Piezoelectric actuators Surface tension driven fluidic actuators

31 Electrostatic comb drive Lee et al. ( ) Sandia National Laboratories (after 2000)

32 Comb drive: a schematic

33 Getting linearity

34 Why is electrostatic force the most popular in microactuators? E t Young s modulus Width of the suspension beams 3 2Etw k 3 l N 0tV Fe 2g 2 w l Lumped mechanical stiffness of the suspension Electrostatic force Thickness of beams Length of the suspension beams g N V Gap between comb fingers Number of comb pairs Voltage F N V l k 4E gw 2 3 e N 0V l l 4E gw V 3 L 2 3 4E gw 2 l N 0 l Deflection of the shuttle Scaling of relative deflection with size for fixed voltage L Scaling of voltage for fixed relative deflection

35 Electrostatic micro motors There was a race between U.C. Berkeley and MIT to make the first rotary motor in silicon.

36 Harmonic micro motor (MIT)

37 Micro gear train (Bell Labs)

38 Micromechanical lock (Sandia) Pin in a maze

39 SUMMiT of Sandia

40 Sandia s microengine gear train

41 Inertial forces can be significant. The inertia may be insignificant but velocities are relatively huge (million rpm is not uncommon). Therefore, inertial forces could be substantial. Figures: courtesy of Sandia National Laboratory

42 Wedge motor of Sandia

43 Our prime mover linkage c/o micro

44 Is electro magnet force not scalable to micro? Electromagnetic force between two coils F 0 2 l II 1 2 d Case 1: Constant current density I J constant = I L F L A Case 2: Constant temperature rise cs J A k T J I L F L L 2 2 s Very, very bad Bad

45 Is electro magnet force not scalable to micro? Between a coil and a permanent magnet F Il B Case 1: Constant current density I J cosntant = I L F L A Case 2: Constant temperature rise cs J A k T J I L F L L 2 2 s Very bad Still bad But with a powerful magnet, one can manage good magnitude of force.

46 Magnetic actuation based pump Kim, Ananthasuresh, and Bau, Balaji and Ananthasuresh,

47 Coils on the chip Fabrication of micro coils is possible but it increases the process complexity. Ahn and Allen, 1993, JMEMS

48 Electro thermal actuation V Cold Hot Bends upwards (Made with PennSOIL) Bends downwards V Undoped Hot Cold (Comtois and Bright s heatuator, 1994) Parallel connection reversed bending Selective doping gives the same effect Bend upwards Many variations with shape, doping, electrical and thermal boundary conditions

49 Enhanced thermal expansion Expansion building block Deformed (Made using MUMPs) (Moulton and Ananthasuresh, 2000)

50 Electro thermally actuated parallel linkages Moulton, Li, and Ananthasuresh, 2001

51 Piezoelectric actuators Active materials that generate electric charge with mechanical strain and vice versa. Typically, have large forces but very small displacements. Usually, used in bimorph mode. Give precise motions. Require large voltages to operate. 800 N Stiffness = 32 N/um Piezo-stack actuator 800 N block force. 25 microns displacement. Force 25 um Displacement

52 Thermo pneumatic actuation A normally closed fluidic valve Trapped fluid Glass Silicon Glass Flow

53 Thermo pneumatic actuation Redwood Microsystems s thermo-pneumatic normally closed valve

54 Pneumatic actuation C. J. Kim, UCLA Bi-metal cantilevers curled due to residual stress. Opened with actuating the bottom membrane

55 Other ways of micro actuation (IISc) I Cell probed with a single contact I Compliant micro mechanism x x O I Input ports actuated by fine-motion stages O Output ports in contact with cell x Observation ports for tracking and force computation x^ ^y ^z Light source Tiltable arm Cell grasped with two contacts for manipulation Compliant micro mechanism I x O O x I Fine motion stage I I Gross motion stage z y x Circular motion stage Controller Microscope Haptic interface for human operator CCD camera PC Image processing Computation of forces and displacements I/O to controller and haptic interface

56 Microactuation with precision stages (IISc) Zebrafish embryo Bio-cell Micromanipulation Setup Close-up of the gripper holding zebrafish embryo PDMS miniature compliant gripper

57 Novel digital speakers Digital reproduction of sound (DRS) Analog Advantages of DRS: Large dynamic range is not necessary. Digital Nonlinearity can be controlled distortion is minimized. Fault tolerance. Intensity control. Speaklets are combined to produce the sound effect. With low-pass filters, the sound is smoothened. Diamond et al., 2003

58 Surface driven flows Several actuation modes by changing surface tension: chemical, thermal, electrical, etc. Cho, Moon, Kim, (JMEMS, 2003) Digital Microfluidics by surface tension driven droplets

59 Power on a chip: MIT microengine A microengine can be made with the same power density as that of a big gas turbine engine. MIT Microengine (Source: Epstein, 2003) Power on a chip Demo engine with H 2 fuel Turbine-compressor test Detail of the DRIEetched blades

60 Smart actuator example S. Dubowsky s group at MIT: Microbot space explorer Supported by NASA Institute for Advanced Research (NIAC) A dielectric elastomer with 200% strain to help microbot hop.

61 Micro actuation macro effect

62 Main points Characteristics of actuators Miniaturization is necessary Because we need to move solids and make the fluids flow. Status Electrostatic actuation is good for sensors. Thermal, magnetic, pneumatic are for real actuation. Piezo and voice coil (electro magnet)are used for precision motion. SMA and other active materials are for special needs. Micro fluidics is going for surface tension, electrophoresis, electroosmosis, etc. Commercial microactuators are not available as standalone devices. Piezo stack actuators are available in large sizes. Much more research is needed on actuators.