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Microrobotic Actuation Mechanisms. Srinivas K. Prasad, MD Johns Hopkins University. Seminar Presentation February 22, 2001. Traditional Surgical Technique. Surgical technique has historically required the establishment of a wide “cone of light” created over a target workspace.

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microrobotic actuation mechanisms

Microrobotic Actuation Mechanisms

Srinivas K. Prasad, MD

Johns Hopkins University

Seminar Presentation

February 22, 2001

traditional surgical technique
Traditional Surgical Technique
  • Surgical technique has historically required the establishment of a wide “cone of light” created over a target workspace.
  • Large incisions and substantial tissue dissection became the rule for these procedures.
  • Patient Morbidity and Mortality was minimized by invoking Listerian principles of Anti-Sepsis and Halsted’s principles of gentle tissue manipulation
minimally invasive surgery
Minimally Invasive Surgery
  • Extrapolation of Halstedian principles prompted the investigation of surgical alternatives to the traditional “cone of light”
  • Advances in Radiology and Fiberoptics Technology have been coupled with simple instrument redesign to enable surgeons to minimize the traumatic extent of exposure and dissection.
  • The Broad Success of Minimally Invasive Surgical techniques has prompted the redesign of several surgical procedures in a variety of disciplines.
challenges for mis
Challenges for MIS
  • Full realization of the MIS vision requires substantial surgical instrument redesign.
  • Traditional instrument redesigns have compromised dexterity and tactile feedback, requiring surgeons to operate within these constraints
  • Harnessing the power of advances in microrobotic and haptic technologies promises to allow surgeons of the future to extend the benefits of Minimally Invasive Surgery to patients across a broader spectrum of disease.
research articles
Research Articles
  • Primary Article: Survey of Microrobotic syntax, design and available technologies.

Dario, P, et al., “Microactuators for Microrobots: A Critical Survey,” Journal of Micromechanics and Microengineering, Sept 1992, pp. 141-157.

  • Secondary Articles:

Monkman, G., “Micro Actuation and Memory Alloys,” Assembly Automation, vol. 16, no. 4, 1996, pp. 22-25.

Suzumori, K, et al., “Applying a Flexible Microactuator to Robotic Mechanisms,” IEEE International Conference on Robotics and Automation, 1991, pp. 21-27.

Hashimoto, M, et al., “Application of Shape Memory Alloy to Robotic Actuators,” Journal of Robotic Systems, vol. 2, no. 1, 1985, pp. 3-25.

syntax microdevices micromachine vs microrobot
Syntax Microdevices: Micromachine vs. Microrobot
  • Micromachine: “A device capable of generating or modulating mechanical work, without necessarily possessing any onboard control”, e.g. micromotor, microvalve or a collection of these devices in a complex, but passive, system.
  • Microrobot: “A device with some form of reprogrammable behavior, or some degree of adaptivity to unpredictable circumstances or remote controllability.
syntax scale considerations
SyntaxScale Considerations
  • Miniature robot:
    • Size & Workspace: few cubic centimeters.
    • Forces: comparable to those applied by human operators during fine manipulation.
    • Interaction: Mechanical
    • Fabrication: Conventional techniques for fabrication of components scaled down to miniature level.
  • Microrobot:
    • Size & Workspace: few cubic micrometers
    • Forces: much smaller for tasks like manipulation of cells and nanorobots
    • Interaction: Mechanical, Electromagnetic Field, Chemical
    • Fabrication: ‘Modified Chip’ design utilizing silicon micromachining technologies for fabrication of micromotors, sensors and processing circuitry.
  • Nanorobot:
    • Size & Workspace: few hundred nanometers
    • Forces: Infinitesimal
    • Interaction: Principally Chemical
    • Fabrication: Nanoscale fabrication techniques for development of molecular mechanical components; Polymer chemistry techniques
  • We will collectively refer to these as Microrobots.
microrobot configurations
Microrobot Configurations
  • Microrobot Components:
    • Physical Structure
    • Controller Unit (CU)
    • Power Source (PS)
    • Actuators for positioning(Ap)
    • Actuators for Operation (Ao)
    • Sensors
  • Microrobot Mobility:
    • Note that the microrobots can be either fixed or mobile
design considerations
Design Considerations
  • These follow from the components and configurations outlined on the previous slide:
    • Degree of autonomy
    • Control Mechanisms
    • Energy Sources
    • Actuation Mechanisms
    • Positioning sensor requirements
    • Haptic Feedback requirements
general microactuation considerations
General Microactuation Considerations
  • Electromagnetic Motors
    • exhibit significant limitations when miniaturized as a consequence of decreased magnetic flux density
    • Require reduction gears to generate useful torques, but these are difficult to fabricate and couple at this scale and they have limited reliability.
  • Microactuation Alternatives
    • Electrostatic Motors
    • Shape Memory Alloy Mechanisms
    • Piezoelectric Mechanisms
    • Rubber Microactuators
electrostatic actuators
Electrostatic Actuators
  • While Electromagnetic Motors are the flagship actuators of macrorobots, Electrostatic Motors have a number of advantages in a microrobotic context:
    • Easily fabricated on silicon wafers
    • High electric fields can be achieved using sub-micron air gaps
    • High rotation speeds can be achieved
    • Control Circuitry can be built onto the same chip
    • Electrostatic force scales down very favorably
    • Can be batch fabricated and coupled on the same chip
shape memory alloy
Shape Memory Alloy
  • SMA is a device that converts thermal energy into Kinetic Energy as a fundamental property of the alloy, e.g. TiNi
  • In particular, these alloys are capable of regaining, either fully or partially, a previous conformation when heated above a characteristic ‘transition temperature’. This is called the Shape Memory Effect.
  • SME is a ‘thermoelastic transformation’ from a ‘martensitic phase’ at low temperature to a ‘austenitic phase’ at high temperature.
properties of sma
Properties of SMA
  • Advantages:
    • SMA’s are very compact, allowing for reduction in overall actuator size.
    • Very high power/weight ratio comparatively
    • Can provide both structural integrity and actuation mechanisms, reducing complexity
    • Accessible voltages can accomplish thermoelastic transformation
    • Electrical Resistance difference between two states can be used as a sensing element to monitor actuator position and force.
properties of sma1
Properties of SMA
  • Disadvantages:
    • Very poor efficiency; Theoretical efficiency ceiling is 10% (Carnot Cycle calculation) but practical efficiency seldom exceeds 1%.
    • Need Mechanism for cooling SMA
    • Regained Conformation with cooling is less predictable
piezoelectric mechanisms
Piezoelectric Mechanisms
  • Piezoelectric devices are based on conversion of electrical energy into mechanical energy through the piezoelectric effect.
  • Ceramics come in a variety of shapes and configurations.
  • Good for generating displacements but of limited utility for exerting operative level forces as a consequence of low work energy density
rubber microactuators
Rubber Microactuators
  • Driven by Electropneumatic or electrohydraulic systems.
  • Easy to miniaturize
  • Many degrees of freedom based on design
  • High power density
  • Smooth behavior
conclusion
Conclusion
  • The frontiers of Minimally Invasive Surgery are rich with possibility as we approach the problem of microrobotic instrumentation from many directions.
  • It is clear that there are many actuation options worthy of investigation and we hope to explore the SMA domain to develop one novel solution in the treatment of Pelvic Osteolysis.