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BIEN 167 Module 6 - Prosthetics & Orthotics

Module 6: Prosthetics and Orthotics (Approaches & Technologies)

 

 

Overview:

The focus of this module is on the functionality of prosthetic and orthotic devices, especially in the context of how the devices are used during relevant life tasks; the biomechanical principles of the human technology interface and physical interfaces in prosthetics and orthotics was addressed in Module 3.

Infrastructure

Prosthetics

Overall Aims

  • Depend in part on functional of level of amputation
  • Depend on relative importance of aesthetics versus function
  • Lifestyle needs and task analysis

Upper Extremity Prosthetics (with historical perspective)

  • Body powered (by early 1950s, post-WWII, core technology was pretty mature)
    • Harness and residual limb interface (see Module 3)
      • Key points: harness can be for stable suspension and/or control; also non-harness systems; concepts of "relief" and "buildup" (biomechanics)
    • Bowden cables (to transmit control and power to 1-DOF terminal device)
    • Terminal device (0- or 1-DOF hook or hand)
      • Options of Voluntary Closing (VC) and Voluntary Opening (VO)
        • Function of user abilities and preferences (VC more natural but often more sustained effort)
        • Either way, spring-loaded return (e.g., elastic band, mechanical spring, pneumatic spring)
  • Externally-powered (1960 to present)
    • Electric power (typically DC motors)
      • Challenges include housing the motor, gearing and battery
    • Pneumatic power (e.g., Simpson group, McKibbon muscles)
      • Advantage is that the mechanical stiffness range is more similar to actual muscles
      • We have used various braided pneumatic actuators (also called McKibbon muscles, artificial muscles, air muscles) laying around, as do other groups.
        • They are easy to make - we had a "make your own" booth at a rehab robotics conference in 1995 (Delaware) that turned on some other groups, and past students have documented their properties. We used them for various projects ranging from anthorobots with large numbers of muscles (late 1980s, early 1990s) to variable stiffness airsprings for large joysticks (here at Marquette). Here's a recent senior design project on YouTube (not sure of university) that used them.
  • During mostly 1980s, some to present:
    • Diversity of Terminal Devices for Body-Powered
    • Novel Electrically-Powered
    • Overview of some basic performance capabilities of natural vs artificial elbows and hands
      • Based in large part on article by Heckathorne in Winters 2008 issue of Capabilities magazine
      • Typical capability in elbow torque (for slow lifts):
        • Natural: ~60-70 Nm typical young adult male, ~50 Nm typical female
        • Otto Bock Dynamic Arm; 18 Nm, Liberating Technologies Boston Digital Arm: 14.2 Nm; Motion Control Utah Arm 3: 4.3 Nm
      • Typical capability for peak elbow speed, for goal-directed point-to-point movement:
        • Natural: ~3 deg/sec for every 1 deg of movement magnitude
        • Prosthetic elbows listed above: can maintain this for up to about 40 deg movements, after which it reaches its peak, such that for large movements its about 1/4 to 1/5 of the natural limb value.
      • Typical capability for finger speed:
        • Natural: over 2000 deg/sec maximum, but for functional "pick-and-grip" tasks, about 170 deg/sec.
        • Prosthetic hands/hooks: cannot attain speeds anywhere near peak finger speeds, but all can get into the "pick-and-grip" range of 170 deg/sec, so are competitive in this regard.
      • Typical capability for grip force (palmer prehension)
        • Both natural and all of the high-end prosthetic hands/hooks (from Otto Bock, Motion Control, Hosmer) are all on the order of about 100 N (or 22 Ibs).
  • Sample of Continuing Research

Lower Extremity Prosthetics (with historical perspective)

Orthotics

Overall Functional Aims

  • To Serve as Functional Splint Across Joint(s)
    • Often at a desired angle for the joint(s), e.g., neutral (note that this can be used to set a posture)
    • Assumes that splint functions as a very stiff spring
  • To Limit Joint Range of Motion (ROM)
    • Low stiffness over a specified ROM, then very stiff splint-like stops
    • Many have a variable lock mechanism
  • To Serve as Functional Spring and/or Dashpot (passive device) Across Joint(s)
    • Springs: provide stiffness, resulting in a length-dependent force and stored potential energy
      • Often designed with a spring functioning in one (weaker) direction
      • Design parameters include stiffness (sometimes variable as function of length), offset
      • Spring materials include conventional springs, bands made of rubber or plastics, pneumatic airsprings, plastic shells
    • Dashpot: provide a viscous-like damping (e.g., to smooth tremors during movements)
  • To Serve as Functional Actuators
    • Many research efforts (since 1950s), but few devices on the market
    • Electric motors (e.g., DC), pneumatic actuator-springs (e.g., braided pneumatic artificial muscles)

Spinal/Cervical Orthotics

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Upper Extremity Devices Available for Purchase

Lower Extremity Devices

 

 

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