Design of a Human Hand Prosthesis

1
Design of a Human Hand Prosthesis Paul
Ventimiglia Liberal Arts Engineering Advisors
Taskin Padir and Jerome Schaufeld

• Key Features
• Completely self contained
• Cosmetic plastic covers
• 6 degrees-of-freedom
• Individually articulated
• Fingertip force measurement
• Variable LED visual feedback
• 1.4 second grasp time from fully open to closed
  power grip
• 410 grams total weight (including battery)

Lithium polymer battery (on back)

• Abstract
•  Current prosthetic hands have limited
  functionality and are cost prohibitive. A design
  of a cost effective anthropomorphic prosthetic
  hand was created. The novel design incorporates
  five individually actuated fingers in addition to
  powered thumb roll articulation, which is unseen
  in commercial products. Fingertip grip force is
  displayed via LEDs for feedback control. The hand
  contains a battery and micro-controller. Multiple
  options for signal input and control algorithms
  are presented. A prototype will serve as a
  platform for future programming efforts.
• Functional Requirements
• 5 individually articulated fingers thumb roll
• Can pick up and hold
• Dime, spoon/fork, common cups/bottles
• Less than 450g total weight
• Minimum power-grip force of 150N
• Minimum pinch-grip force of 15N
• Multiple user-control input options
• Less than 3,000 to produce (Quantity 1x)

Thumb joint/gearbox
Finger pivot joints
Compound thumb gearbox

• Control Considerations
• Arduino Pro Mini for I/O and onboard processing
• Analog potentiometers measure the rotational
  position of each finger joint
• Fingertech TinyESC motor controllers
• Open source serial input allowing for multiple
  signal input options
• Myoelectric
• Toe-operated wireless switches
• Multiple grip mode algorithms

½-20 stud universal mount
Example of commonly used prosthetic hook
Rubber grip lining on fingers
Main finger motors/gearboxes
Thumb roll motor

• Finger Linkage Motion
• Single driven joint
• 4-bar linkage provides human-like motion of the
  finger tip
• Finger tips act as a spring in series to provide
  constant holding force and impact absorption
• Conformal gripping of common objects

• Manufacturing Considerations
• Utilization of many COTS components when
  applicable
• Entire cost to build fully functional prototype
  is 2,500
• Several plastic components were designed for
  plastic injection molding
• Universal components used extensively throughout
  the design

Grip Mode Examples
Open Palm Grasp (thumb remains open)
Power Grip (all fingers are powered)

• Conclusions
• A complete mechanical design and prototype were
  produced
• Worm gear joints and linkages provided compact
  packaging
• A solution for an integrated thumb roll gearbox
  was developed
• Many COTS components allowed for cost reduction
• There is room in the market for lower cost
  prosthetic options
• Future Recommendations
• User testing and analysis for ease of use and
  controllability
• Programming new grip algorithms
• Additional force sensor integration on multiple
  fingers
• Wireless control through external signal inputs
• Durability and strength testing of prototype

• Finger Joint Drivetrain
• DC-brushed motor with 2501 spur gear reduction
• 121 48 DP worm gear final reduction
• 2-start leads for increased efficiency
• Anti-backdrive allows for constant fingertip
  holding force without active power application
• Precision ball bearings for transmission
• 7075 Aluminum axles

Key Grip (thumb is powered)
Precision Pinch (index finger is powered)