e-NABLE Hand Test RigP16061David Schwartz, Tia Parks, Shannon Barry, Samantha Mason, Charles Rumfola

Agenda● Recap

○ Problem Statement○ Customer Requirements○ Engineering Requirements

● Subsystems○ Clamp Selection○ Controller/Processor Selection○ Display Data Analysis○ Motor Feasibility○ Data Collection Feasibility

● Design Drawings● Bill of Materials● Risk Assessment● Plans for Next Phase

Problem Statement● Current State

○ David Schwartz developed a prototype for measuring grip strength. It functions, but lacks the amenities desired for the final design.

● Desired State○ A functioning prototype that can be used to test different types of e-NABLE devices.○ Device should be able to be replicated because e-NABLE is a global and open source community.

● Project Goals○ Analyze the current accepted methods of testing grip strength.○ The apparatus must be:

■ Easy to Use■ Portable■ Cost Effective■ Repeatable

● Constraints○ Cannot disassemble or break the hand in the process of measuring grip strength.○ Cost of end product should cost under $200 to produce.

Customer Requirements

● Inexpensive, $200 should be the maximum for construction● Portable● Repeatable● Adaptable to other prosthetic models● Easy to use● Continuous Data Acquisition● Does not alter prosthetics or remove any pieces● Test the full hand strength, an overall grip strength test

versus the angle of the wrist flexion

Engineering Requirements

Requirement # Importance Metric Unit Target Value Subsystem

S1 9 Cost $ 200 Entire Apparatus

S2 6 Weight of Tester lbs 50 Entire Apparatus

S3 5 Duration of Test min 5 Motor

S4 8 Force Measurement Accuracy oz 1 Load Cell and Amplifier

S5 8 Angle Measurement Accuracy ° 2 Motor / Data Acquisition

S6 9 Max Force of Sensor lbs 50 Load Cell

S7 8 Torque oz/in 250 Motor

Clamp Testing

Trip to Home Depot

Clamp Selection

6 in. Medium Trigger Clamp$10.97

http://www.homedepot.com/p/DEWALT-6-in-Medium-Trigger-Clamp-DWHT83139/204389199

Controller / Processor SelectionHigh Level Understanding of Electronics

● Microprocessor - Processes Data● Microcontroller - Control Motor● Arduino - Controls motor and processes data

Assumptions:● All controllers will be compatible with our other electronics.● Users will have access to a computer with Excel or will be able to download an open

source program.

Analysis:● Based on research and analysis we have found that Arduino is compatible with Excel. It is

also easy to use, controls and processes data, and is open source.

Display Data Analysis● External

○ LED Display○ SD Card

● Computer○ LabVIEW Interface○ “Graph” Function○ Microsoft Excel

■ PLX-DAQ■ “GoBetwino” Function

Motor Feasibility - Torque Requirements● Torque requirements determined through

measuring e-NABLE gauntlet length and max force exerted

● Due to the small sample size and uncertainty of the data, the highest value calculated was multiplied by a factor of 3 to yield our basis for holding torque

● _max = 11.79 lb*in (189 oz*in)

NameMax

ForceGauntlet Length

Calculated Torque (F*L/2)

Torque Value

Raptor (Green) 1 lb 2 oz 4 in 2.25 lb*in 36 oz*in

Raptor (Blue) 1 lb 1 oz 3.4 in 1.81 lb*in 28.96 oz*in

Raptor (Black and White w/ Whippletree)

1 lb 13 oz

4.33 in 3.93 lb*in62.88 oz*in

Servo vs. Stepper Motor

● Servo Motor○ Maintains torque at high speeds○ Requires encoder to track position○ More prone to fatigue and degradation

● Stepper Motor○ Higher maximum torque, but degrades faster with higher○ Finite number of angular positions○ Built-in angle sensor

Stepper was chosen because we do not foresee any need for the motor to move quickly, to eliminate the need for an angle sensor, and to be cost effective.

Stepper Motor Pugh Chart● Stepper Online Nema 23

○ $24.42○ Requirements - 24-48V, 2.83A○ Holding Torque - 283 oz*in○ Step Angle - 1.8°

● Pololu 1477○ $49.95○ Requirements - 8.6V, 1.0A○ Holding Torque - 190 oz*in○ Step Angle - 1.8°

● Robotshop Nema 17○ $48.00○ Requirements - 12V, 1.7A○ Holding Torque - 667 oz*in○ Step Angle - 0.018°

● MPJA Nema 23○ $23.95○ Requirements - 5.7V, 2.3A○ Holding Torque - 222 oz*in○ Step Angle - 1.8°

Criteria Stepper Online

Nema 23

Pololu 1477 Robotshop Nema 17

MPJA Nema 23

Cost

Datum

- - +

Required Voltage + + +

Required Current + + +

Holding Torque - + -

Step Angle S + S

+

Datum

2 4 3

S 1 0 1

- 2 1 1

Total 0 3 2

Stepper Motor Pugh Chart Cont.Criteria Stepper Online

Nema 23 Pololu Robotshop MPJA Nema 23

Cost + -

Datum

+

Required Voltage - + S

Required Current - + -

Holding Torque - - -

Step Angle - - -

+ 1 2

Datum

1

S 0 0 1

- 4 3 3

Total -3 -2 -2

Adafruit Motor/Stepper/Servo Shield● Can drive motors

from 4.5 V-13.5 V

● Compatible with Arduino software

● Tested and warrantied

● Price: $19.95

Data Collection

Systems Design phase left us between these two designs:

Strain Gauge Load Cell Finger Sensors

Data Collection (Finger Sensors vs Strain Gauge)

Strain Gauge Load Cell-Measures accurate whole hand grip-More portable than 5 sensors-Less expensive-Has higher force range-Harder to mount

Finger Sensors -Measure individual finger strength-Can tell if one finger is -applying more/less force than another-Less accurate especially with whole hand grip

Overview:

Can Measure

Pinch Grip

Data Collection (Pugh Chart)

Criteria FSR (0.5”)

FSR (0.3”) Piezoelectric Sensors

Strain Gauge

Load Cell

Cost

Datum

- - +

Ease of Mounting S - -

Accuracy S + +

Programmability S S +

Ease of Obtaining S - S

Force Range S + +

+

Datum

0 2 4

S 5 1 1

- 1 3 1

Total -1 -1 3

Conclusion: Strain Gauge Load Cell is the best option

But since FSR’s are cost effective and easy to use this will still be tested as a backup plan.

Types of Load Cells

Source: http://www.loadstarsensors.com/what-is-a-load-cell.html

Criteria

Cost

Datum

- + +

Force Range + + +

Accuracy - - +

Ease of obtaining S S S

+

Datum

1 2 3

S 1 1 1

- 2 1 0

Total -1 1 3

Conclusion: Bar Single Point load cell will be the best (Most accurate/cost effective) (Link)

Load Cell (Pugh Chart)

Load Cell SelectionConclusion:

● Cost Effective● Measures higher than

needed force range● Very Accurate● Excellent off center loading

compensation

Price: $7.00

50kg Single Point Load Cell

Design Isometric View

Design Top-Down View

● Modular○ Can account for

arms○ Can account for

different grip positions

Bill of MaterialsID Part Name Quantity Price/Unit Total Price Make/Buy1 Arduino Uno 1 $24.95 $24.95 Buy2 Stepper Motor 1 $23.95 $23.95 Buy3 Wood Base 3 - - Acquire4 Wooden Wheel 1 $5.85 $5.85 Buy/Make5 Clamp 1 $10.97 $10.97 Buy6 Sensors 5 $8.95 $44.75 Buy7 Load Cell 1 $7.00 $7.00 Buy8 Motor Shield 1 $19.95 $19.95 Buy9 Wooden Dowel 1 $6.94 $6.94 Buy

10 Screws 4 - - Acquire11 Op Amp 1 $6.43 $6.43 Buy12 Power Supply 1 $11.34 $11.34 Buy

Total - - $162.13 -

Block Diagram

Risk AssessmentRisk Assessment

Plans for Next Phase