Design of Miniature Manipulators For Integration In A Self Propelling Endoscope

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Design of Miniature Manipulators For Integration
In A Self Propelling Endoscope

• Pratheek Pamidimukkala

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Abstract

• The endoscope is meant to inspect and intervene
  in the human colon through which it moves by inch
  worm motion.
• The manipulator is used to orient camera and
  tools

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Contd..

• Three different prototypes have been realised
• A first design is based on a 3 degree-of freedom
  (dof) Stewart platform driven by hydraulic
  pistons.
• A second design is based on a Stewart platform
  with three telescopic legs, each driven by an
  electromagnetic motor with spindle.

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Contd..

• The third design is a serial arm consisting of
  two links. Both links are driven by an
  electromagnetic motor with worm gear reduction
• This simple design combines the compactness of
  the first design with the controllability of the
  second design.

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Introduction
Fig 1. Self Propelling Robotic Endoscope
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Contd..

• The endoscope (fig.1) consists of a propulsion
  unit, a miniature robotic arm, and a tail.
• The propulsion unit consists of two suction
  clamps connected by an expansion bellow
• The tail connects the endoscope to the outer
  world and contains electrical wiring, pneumatic
  tubes, tool channel, etc

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Hydraulic manipulator design
Fig. 2 Hydraulic manipulator design
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Contd..

• The design of hydraulic manipulator (fig.2) is
  based on a 3 degree-of-freedom (dof) Stewart
  platform.
• The platform is driven by three hydraulic pistons
  which are connected to the upper platform through
  ball joints which are formed by a steel ball
  clamped between two PTFE (teflon)discs.
• Advantage is its high stiffness and the
  possibility to have a tool channel running
  through the center.

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Hydraulic Manipulator prototype
Fig.3 Hydraulic manipulator prototype in two
extreme positions
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Contd..

• All parts have been made by a combination of
  turning, milling, drilling, grinding, wire-EDM
  (Electro-Discharge Machining), and micro-EDM.
• The figure shows the prototype in two of its
  extreme positions. On the left, the manipulator
  is in its lowest flat position. On the right, the
  manipulator is in the fully extended position
  while maximally rotated.

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Hydraulic prototype tests

• The kinematics of the hydraulic micromanipulator
  work well and the construction is rigid and
  stiff.
• Main problem is the friction between rubber
  o-rings and the stainless steel cylinder block.
• The static friction ranges from 0.4 to 0.9 N,
  depending on piston and cylinder, but also on the
  time the piston has not moved. The longer the
  piston is standing still, the higher the static
  friction.

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Valve integration

• To keep the tail of the self propelling endoscope
  as flexible as possible, the number of hydraulic
  tubes should be as low as possible.
• To reduce the number of tubes, valves are under
  development that can be integrated into the
  manipulator or endoscopic system.
• The idea is to integrate the valves in the
  actuator block, to enhance miniaturisation and to
  simplify assembly and hydraulic interconnection.

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Electric Stewart platform

• The platform has three telescopic legs, each
  driven by a combination of an electromagnetic
  micromotor and a microspindle
• It consists of two concentric tubes.
• In the inner tube, motor, spindle and bearings
  are mounted.
• The outer tube is connected to the spindle nut
  through a sleeve in the inner tube.

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Fig.4 Electric leg design and prototype
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Electric leg prototype

• The leg prototype shown in the figure 4 is in its
  shortest state.
• Spindle, inner and outer tube, and the ball joint
  are made of stainless steel.
• Nut, coupling and bearing seats are made from
  brass. The parts are made by a combination of
  turning, wire-EDM and micro-EDM.
• A linear potentiometer is attached for position
  measurement

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Electric leg characterisation

• Due to simplicity of the set-up, the influence of
  load on speed could only be tested for speeds up
  to 2 mm/s
• At zero load, the maximum speed of the leg is 5
  mm/s due to the speed limitation for the motor
  reduction.

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Fig.5 Serial module design and prototype
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Serial manipulator design

• It is based on a serial combination of two
  modules with one rotational dof as shown in
  figure 5.
• A large hole runs through the module to pass the
  tool channel, camera wiring, illumination fibres,
  and flushing channel.
• The module is driven by a miniature gearmotor
  through a worm gear reduction.

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Fig.6 Integration of the serial manipulator
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Integration in the endoscope

• The manipulator requires two dofs, such that two
  modules have to be put in series as shown in
  figure 6.
• Advantageous is that camera is integrated into
  the front module while the other module is for a
  large part integrated into the frontal clamp.
• Therefore, the arm extends only 40mm at the front
  of the propulsion module.

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• Both rotation axes are located close to each
  other such that the manipulator characteristics
  in both directions are nearly identical.
• Rubber bellows seal the manipulator.

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Comparison of the manipulators
Table.1 Comparision of manipulators
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Conclusions

• The hydraulic Stewart platform is compact and
  generates high forces.
• The main drawbacks are the high friction, the
  difficulty to control it, and the relatively
  stiff tubing.
• The electric Stewart platform is much easier to
  control but is too large.

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• The serial manipulator has the simplest design
  and uses a compact worm gear reduction.
• Therefore, the serial manipulator combines
  compactness with the controllability of
  electromagnetic motors
• In case its output torque can be increased, it
  can be regarded as the best solution.

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References

• "Design of miniature manipulators for integration
  in a self-propelling endoscope",
  J. Peirs, D. Reynaerts, H. Van
  Brussel, Proc. of Actuator 2000, 7th
  International Conference on New Actuators, Bremen

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Thank You Any questions??