Design of a Human Hand ProsthesisDesign of a Human Hand ProsthesisPaul Ventimiglia

Liberal Arts & EngineeringAdvisors: Taskin Padir and Jerome Schaufeld

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/bottlesLess than 450g total weight Minimum power-grip force of 150NMinimum pinch-grip force of 15NMultiple user-control input optionsLess than $3,000 to produce (Quantity 1x)

Key FeaturesCompletely self contained

Cosmetic plastic covers6 degrees-of-freedom

Individually articulatedFingertip force measurement

Variable LED visual feedback1.4 second grasp time from fully open to closed power grip410 grams total weight (including battery)

ConclusionsA complete mechanical design and prototype were producedWorm gear joints and linkages provided compact packagingA solution for an integrated thumb roll gearbox was developedMany COTS components allowed for cost reductionThere is room in the market for lower cost prosthetic options

Future RecommendationsUser testing and analysis for ease of use and controllabilityProgramming new grip algorithmsAdditional force sensor integration on multiple fingersWireless control through external signal inputsDurability and strength testing of prototype

Finger Joint DrivetrainDC-brushed motor with 250:1 spur gear reduction12:1 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 transmission7075 Aluminum axles

Grip Mode Examples

Power Grip(all fingers are powered)

Open Palm Grasp(thumb remains open)

Key Grip(thumb is powered) Precision Pinch

(index finger is powered)

Finger pivot jointsFinger pivot joints

Thumb joint/gearboxThumb joint/gearboxLithium polymer Lithium polymer battery (on back)battery (on back)

Compound Compound thumb gearboxthumb gearbox

½-20 stud½-20 studuniversal mountuniversal mount

Thumb roll Thumb roll motormotor

Main finger Main finger motors/gearboxesmotors/gearboxes

Rubber grip Rubber grip lining on fingerslining on fingers

Control ConsiderationsArduino Pro Mini for I/O and onboard processing Analog potentiometers measure the rotational position of each finger jointFingertech TinyESC motor controllersOpen source serial input allowing for multiple signal input options

Myoelectric Toe-operated wireless switches

Multiple grip mode algorithmsExample of commonly used prosthetic hook

Manufacturing ConsiderationsUtilization of many COTS components when applicableEntire cost to build fully functional prototype is $2,500Several plastic components were designed for plastic injection moldingUniversal components used extensively throughout the design

Finger Linkage MotionSingle driven joint4-bar linkage provides human-like motion of the finger tipFinger tips act as a spring in series to provide constant holding force and impact absorptionConformal gripping of common objects