Robotic Limb for Above Knee Prosthesis

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Robotic Limb for Above Knee Prosthesis
May 2004

• Intelligent Robotics For Rehabilitation

Project Guides R. K. Sharma (ECE) Dr. R. P.
Tewari (ICE) Vicky Suri (ICE)
Sameer Singh 83 ECE 2k Shuja Hussain 101
ECE 2k Raman Agarwal 449 ICE 2k
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Objectives

• Natural Looking Gait
• Customizable for Different Users
• Automatic Operation
• Low Cost
• Low Weight
• Low Power Consumption

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Existing Technology

• About 50 different types of prosthetic legs
• Most have Passive Control
• Limited control over the Gait
• Hydraulic or Pneumatic as dampers
• Some use bio-feedback
• C-Leg by Otto Bock is one of the few with
  microprocessor control
• In India, the crude Jaipur Leg.

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Our Approach
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Software

• Resides on the PC
• Divided into
• Gait Cycle
• Curve Generation
• EPROM File
• The section as a whole takes the user
  information, and generates an EPROM file for the
  microcontroller

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Gait Cycle

• Walking has four important functions
• Essential Functions
• Progression
• Weight Bearing
• Non-Essential Functions
• Shock Absorption
• Energy Conservation
• For our purpose, we shall only concentrate on the
  essential functions

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Gait Parameters
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Gait Parameters
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Curve Calculation

• Time based Parameters (Stride Time) and Physical
  parameters (Stride Length) not used in this part.
• The gait cycle needs to be drawn from the given
  user parameters of the curve shape.
• Wherever parameter not available, use average or
  nominal value

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Hermite Curves

• Borrow algorithm from computer graphics.
• Four points for a 2D curve interpolation, i.e.
  P1, P2, R1 R2. Curve is drawn between P1 and
  P2, with the derivatives R1 and R2 at these
  points, respectively.
• X(t) (2t3 3t2 1)P1x (-2t3 3t2)P2x (t3
  2t2 t)R1x (t3 t2)R2x
• Y(t) (2t3 3t2 1)P1y (-2t3 3t2)P2y (t3
  2t2 t)R1y (t3 t2)R2y

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Hermite Curves
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EPROM File

• Clipping - Extra points clipped from the curve
• Sampling - Sampled to get 100 points
• Quantizing - Convert from float (0.0-90.0) to a
  byte value (0x00 0xFF)
• Header Information - Additional Information added
  like stride time, user weight threshold, user
  name, etc.
• Programming - EPROM File programmed into the
  microcontroller

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Electronics

• Sensors Switches
• Microcontroller
• Microcontroller Code
• EPROM Programmer
• Motor Control
• Valve Control

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Sensors Switches

• Knee Angle Sensor
• Force Sensor
• Vibration Sensor
• P/E Switch
• Speed Knob
• Emergency Release Key

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Microcontroller Requirements

• EPROM 128b
• FLASH - for 3-4 kb program
• In built ADCs 4
• I/O Pins 25
• In Built Timer 16 bit
• In-System Programming
• Low Cost Availability

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Microcontroller I/O Pins
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Microcontroller Code

• Consists of mainly 2 alternating methods, namely
  actuation control and timer.
• Timer generates an interrupt every
  (stride_time)/100 since 100 points. Also updates
  desired_angle.
• The second method moves actuation one step either
  side to achieve desired_angle

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Microcontroller Code

• Other methods
• Force Threshold
• Vibration Start / Stop
• Actuation Release
• Update Speed
• Programming Mode

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EPROM Programming

• Connected to PC using the Parallel port
• Pon, Clk and ltDatagt input to microcontroller,
  while Ack output from microcontroller
• Pon denotes programming mode of PC and is level
  triggering
• Clk and Ack signals are identified when their
  values are toggled.

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EPROM Programming
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Motor Control Circuit
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Valve Interfacing Circuit
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Mechanical

• Motor used for Actuation
• Pneumatic Damping used for Shock absorption
• Hydraulic rejected due to weight
• Flow Valves to control speed
• Electro-pneumatic valves (3/2), i.e. 3 ports
  (exhaust, pressure output) and total 2 states
  (output connected to each)

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Pneumatic System
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Working of the Leg
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Mechanical Drawings
Key 1 Upper Limb 2 Air Cylinder 3 Lower
Limb 4 Motor Support Plate 5 Motor Flange
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Photographs
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Future Work

• PCB Fabrication
• Carbon Fiber Body
• Better Motor
• Force Sensor
• Angle Sensor
• Hydraulic Damping
• Better Response Valves
• Vibration (or Myo) Sensors

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References

• Wilson, A. Bennet, jr., Limb Prosthetics. Sixth
  Edition, Demos Publications, New York, 1978.
• Vitali, Miroslow, Amputation and
  Prosthesis.Cassel Co., Ltd. London, England,
  1978.
• Eberhart HD, Inman VT, Bresler B. The principal
  elements in human locomotion. In Klopsteg PE,
  Wilson PD, editors. Human limbs and their
  substitutes. New York McGraw-Hill 1954. p.
  437-71.
• Murray MP, Drought AB, Kory RC. Walking patterns
  of normal men. J Bone Joint Surg 1964 46A
  335-60.
• James, K.B. System for Controlling Artificial
  Knee Joint Action in an Above-Knee Prosthesis (US
  Patent No.- 5571205)
• Perry, J and Ayyappa, E Assessment of external
  prostheses in Rehabilitation. Edited by
  Goldstein, G and Beers, SR. 155-168. Plenum
  Press, New York, 1998.
• JR Gage, PA DeLuca, TS Renshaw Gait Analysis
  Principles and applications. Emphasis on its use
  in cerebral palsy. Journal of Bone and Joint
  Surgery, 77A 1607-1623, 1995.
• Ju, M.S., Yi, S.H., Tsuie, Y.G. Chou, Y.L.
  Fuzzy Control of Electrohydraulic Above-Knee
  Prostheses. Int. Conf. on Prosthetics, London
  (1998).
• Computer Graphics Principles Practice Foley,
  J.D., van Dam, A., Feiner, S.K. Hughes, J.F.
  (Pearson Education)
• Programming and Customizing the AVR RISC
  Microcontrollers Gadre, D.V. (McGraw Hill)

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Thank You

• Sameer Singh 83 ECE 2k
• Shuja Hussain 101 ECE 2k
• Raman Agarwal 449 ICE 2k