SHAPE MEMORY MICRO ACTUATION FOR A GASTRO_INTESTINAL INTERVENTION SYSTEM

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SHAPE MEMORY MICRO ACTUATION FOR A
GASTRO_INTESTINAL INTERVENTION SYSTEM

• by
• RAGHUNANDAN REDDY POTHALA

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Topics

• Introduction
• Design of gastro intestinal intervention system
• Design of modular bending actuator
• Construction of an optimized actuator prototype
• Production of actuator elements
• Conclusion

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Introduction

• This paper describes the design of a prototype
  gastro intestinal intervention system based on an
  inchworm type of mobile robot.
• By intermittent clamping ,expanding and re
  clamping these robots can creep over a rod or
  inside a tube.
• The most promising future for these robots lies
  in the field of inspection and intervention in
  medical as well as industrial applications

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Design of gastro intestinal intervention system
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• Initially operation in the blood stream was
  mostly in the application.
• drawbacks
• the free floating devices has to cope up with
• the reaction of the immune system on strange
  objects.
• blood clotting around the objects.
• ability to navigate in viscous environment,
  sometimes against the blood flow.

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• The translation module expansion can be realized
  with a spring type SMA actuator.
• The clamping module must be able to clamp in a
  human column with a diameter ranging from 15 to
  50mm.
• The bending module has to realized a bending
  from -45 to 45 degrees.

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Design of modular bending actuator
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• The actuator can be compared to a single vertebra
  stacking several elements can form a spinal
  column. Each vertebra is controlled in a binary
  mode.
• It consists of a central rotating part actuated
  by two antagonistic SMA actuators.
• The central element also contains two return
  springs with constant and equal torques. This
  mean the unpowered position corresponds to the
  neutral position.

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• Since actuators are controlled in binary ,only
  mechanism for selection of different actuators
  has to be provided.
• The electrical control of the
• different actuators can be
• realsied with a
• bus system.
• In figure adjacent modules can be rotated 90 deg
  to each other so that 2-D bending actuator is
  obtained.

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• Based on the above signals two principles used
  for driving the different actuators.
• The first one realises actuator selection with a
  filter or a phase locked loop. This allows
  simultaneous actuation using only one select
  signal.
• drawback all modules differ by their filter
• The second principle uses digital addressing of
  different modules . This also enables
  simultaneous actuation but requires additional
  clock channel.
• Adv All modules differ by address

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Construction of an optimized actuator prototype
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• Both parts are connected to each other via two
  super elastic joints.
• Heating both parts same time has to be avoided
  as this will overload both strips and joints.
• The body of actuator consists of two parts, an
  upper and a lower part.
• Mechanical stop guarantees a fixed distance
  between the SMA strip and the axis of rotation.
• A 15mm thin glass pate assures thermal and
  electrical isolation between the SMA strip and
  the aluminum body.
• Assembly of all parts is done by gluing

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• To obtain the specified stroke three actuators
  have to be used activation of one. Two or three
  actuators causes 15 30 and 45 deg rotation.
• Seven useful combinations are possible leading
  to
• following positions -45 -30 -15 0 15 30 45
  degrees.

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The actuator contains two super elastic joints
with dimensions . Two joints on each side of
the actuator are used to enhance stiffness and
strength in the other direction. They are made
of a CuINi alloy by EDM. An elastic join exhibit
no friction or backlash. An elastic joint with
the same stiffness in the neutral position needs
a 5 times higher torque to bend it to its extreme
position.
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Production of the actuator elements

• The low electric resistance in SMA actuators can
  be increase by replacing the ribbon by a number
  of wires mechanically in parallel and
  electrically in series.

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• For realizing a pattern ribbon several
  technologies are proposed-EDM ,laser cutting and
  etching.
• Wire EDM has the disadvantage that a startling
  hole is needed for the wire unless the wire
  starts from the side of the work piece. The wires
  are .3mm wide and 5.5mm long.
• Laser cutting is faster and allows more complex
  patterns. Laser cutting was performed in an argon
  atmosphere because of the high reactivity of
  titanium with oxygen. The co2 laser cut ribbon
  with wires of .2mm wide and 5mm long. The cut
  surface is very rough which is disadvantage.
• Superior results were obtained with an excimer
  laser.
• Etching NiTi is a problem because of its high
  resistance. FeCl3 gave good results

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Conclusion

• Among the several design alternatives a straight
  wire system with antagonistic actuator is the
  best.
• Several technologies for producing straight SMA
  elements with high resistance were discussed .
  Excimer laser cutting gave the best results.

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References

• http//www.molecularassembler.com/KSRM/Refs1200-12
  99.htm
• http//www.arts.sssup.it/people/prof/pdario/pdario
  .htm
• T. Fukuda, H. Hosokai, H. Ohyama, H. Hashimoto,
  F. Arai, Giant Magnetostrictive Alloy GMA.
  applications to micro mobile robots a micro
  actuator without power supply cables, Proc. IEEE
  Micro Electro Mechanical Systems, Nara, Japan,
  Jan. 30Feb. 2, 1991, pp.