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Powered Hip Exoskeleton

Presented by the Biomechanical Capstone team

Team members:�Daniel Colley�Kyle Shough�Nathan Stewart�Sharon Toenjes�Jeffrey Yows

Nathan Stewart

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Problem Breakdown – SOTA Review

More than 1 in 600 children are born with cerebral palsy (CP)

Gait training focused on correcting movements has shown to improved motor control allowing children with CP to walk again

The extensive training required is physically and mentally difficult

Therapists have a difficult time monitoring and correcting gait

Daniel Colley

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Problem Breakdown – SOTA Review

Developing technologies in robotics has made the development of exoskeletons a viable solution to rehabilitating those with walking disabilities

Current systems are functional but are often too heavy for children and cannot provide assistance at high walking/running speeds

A more robust, low profile, and lightweight exoskeleton is needed to assist rehabilitating children with CP

Nathan Stewart

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Problem Breakdown – Old Cable System

Retro-fit a Hip Exo-skeleton with a light weight, belt driven system
Reasons for the Change:
Belt drive systems are robust
Can apply more Power than the cable/pulley system
Suitable for running
Provides more assistance

Figure 1: Bowden Cable Exoskeleton

Sharon Toenjes

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Customer Requirements

Safe Operation

Improved Walking Assistance

Low Profile Design

Comfortable

Three Degrees of freedom

Within Budget

Client: Dr. Lerner – CTO of Biomotum Inc.

Kyle Shough

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Engineering Requirements

Safe Operation

NEMA 1 Enclosed System

Improved Walking Assistance

10 N∙m @ 400°/s Hip Joint Moment

Low Profile Design

< 40 mm Frontal Plane Protrusion

Comfortable

< 3.0 kg Exoskeleton Weight

< 40 mm Lateral Plane Protrusion

Three Degrees of Freedom

35⁰/15⁰ Flexion / Extension

50 ⁰ Abduction /Adduction

50⁰ Internal /External Rotation

Within Budget

Project Cost < $2000

Kyle Shough

After our teams meeting with the client we broke down the list of customer needs into engineering requirements. We defined each of our engineering requirements into quantitative terms that we could measure and evaluate. We determined that an enclosed housing around the belt drive transmission would be sufficient to provide safe operations. We have a target goal to reach a NEMA 1 encloser rating, which means that the housing will prevent falling dirt and fingers from accessing to the moving components within the housing.

We determined that the best way to improve the walking assistance is to increase the torque output of the hip joint, we have a set torque goal of 10 Nm. In order to maintain a low profile design we would like reduce the systems frontal plane protrusion, with a target goal of less than 40 mm. We decided that comfortability can be defined as the overall weight of the system, as well as the lateral plane protrusion. We have a design goal of less than 1.5 kg and less than 40 mm in lateral protrusion. We determined that the three degrees of freedom we need are in flexion and extension, abduction and adduction, and internal and external rotation. Our targets are a range of motion of 35 degree in flexion, 15 in extension, 50 degrees in both abduction and adduction and internal and external rotation. These numbers derive from a healthy persons average range of motion while walking. Lastly, we need to make sure that our total project cost is within $2000.

The National Electrical Manufacturers Association (NEMA)

NEMA 1

Indoor use to provide a degree of protection to personnel against access to hazardous parts
To provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt)

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Design Solution

Features:

16 Nm of Torque (Max)
2.8 kg total weight (6.2 lbs.)
3 DOF-Full Range of Motion
38 mm Lateral Protrusion
Size adjustable
Motion Censored Control
NEMA 1 Enclosure
Project Cost < $2000

Figure 2: Final Design Solution

Daniel Colley

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Ranking Importance of Engineering Requirements

General Order of Importance

Weight
Flexion / Extension
Hip Joint Moment / Speed

Lateral Protrusion
Internal/External Rotation
Adduction/Abduction

Frontal Protrusion
Enclosed System
Project Cost

Table 1: Quality Function Deployment (QFD)

Level of Importance

Daniel Colley

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Decision Making

Initial Design Concepts

Figure 3: Initial Motor Placement Concepts

Figure 4: AK60-6 Motor

Figure 5: Maxon Motor

Daniel Colley

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Decision Making

Iteratively found the smallest solution That does not interfere with user

Found the nearest commercially available belt length

Significantly reduced the total length

Originally longer to prevent the motor from protruding into user

Device Length & Fit

Figure 6: Long Plate

Figure 7: Short Plate

Nathan Stewart

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Decision Making

Able to withstand a 15Nm torque and 15 N tension
Expensive to manufacture due to unique features

Required a service like Protolabs

Frontal Protrusion did not satisfy the client

Original Motor Hub Design

Figure 9: Stress Analysis FEA: Pinion Gear

Figure 8: Initial Motor Hub Design

Jeffrey Yows

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Decision Making

Keyway increased strength and reliability

Industry standard

Simple enough to make in house
Reduced belt width:14mm 6mm
Kevlar

2x rate torque output of Fiberglass
Low supply and long lead time

Fiberglass

Readily available

Final Motor Hub Design

Figure 10: New Motor Hub

Kyle Shough

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Decision Making

Figure 11: Original Requirements and equations

Table 2: Gearbox calculation results

Motor Hub Design

Kyle Shough

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Decision Making

Reduced gear ratio- 3:1-2:1

Client want to further reduce the size of system

Belt Drive Tensioning Method

Geometric tensioning

Calculated w/ design tool
Low Profile-build in

Adjustable tensioning

Hard to design within size limit

Torque Transmission Design

Figure 12: Gear Box Section View

Daniel Colley

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Decision Making

Onyx Filament

Cheap and easy to make parts with
Significantly lighter
Can be reinforced with Carbon fiber
Had a similar FOS as 1060 aluminum

Aluminum

Costs more
Harder to manufacture
Longer lead time required

Material Analysis

Figure 13: Aluminum FOS: 32 Nm of Torque

Figure 14: Nylon FOS: 32 Nm of Torque

Jeffrey Yows

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Decision Making

Design Optimization

Powertrain Size = f(frontal protrusion, lateral protrusion)

Frontal protrusion = f(center distance, torque rating)
Lateral Protrusion = f(torque rating / bearings & fasteners)
Torque Rating = f(center distance, belt width, diametrical pitch, belt material, tooth profile)

Daniel Colley

Streamlined Housing

Carbon Fiber to Onyx
Integrated structural components
Reduced lateral protrusion & weight
Simplified manufacturing & assembly

Optimized Power Transmission

Reduced friction using ball & needle-roller thrust bearings

Needle-roller thrust bearings fix the pulley’s axial position

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Failure Modes and Effects Analysis

Table 3: FMEA

Decision Making

Sharon Toenjes

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Manufacturing Process

3D Printing Considerations

Print Orientation

Carbon Fiber Infill

Tolerances

Figure 15: 3D printed components and equipment

Jeff Yows

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Manufacturing: Motor Hub

Figure 16

Figure 17

Figure 18

Figure 19

Nathan Stewart

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Figure 20: Pulley & Shaft Operations

Figure 21: Keyway & Pulley operations

Manufacturing: Pulleys & Shaft

Nathan Stewart

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Figure 22: Various steps of the assembly process

Figure 23: Powertrain Assembly

Manufacturing: Powertrain Assembly

Nathan Stewart

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Testing Final Project Solution

Thermal Safety Test

NEMA 1 Enclosure Test

ER Requirements:

Safe Operation
Comfortable

Procedure:

Prolonged Usage of motor
5–10-minute motor powered
Correct toque applied
Collect Data in 30 second Increments

Measurements:

Temperature Of motor
Temperature Of surrounding Components

Resources/Equipment

Device
Lab Facilities
Lab control Software

ER Requirements

Safe Operation
Low Profile Design

Procedure:

Dirt poured top, sides, and bottom of Enclosure
Attach and Remove Device

Measurements:

Meets NEMA 1 Enclosure Standard
Enclosed Device
Dirt may fall on it

Resources/Equipment:

Device
Dirt (30g)
Outside

Sharon Toenjes

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Testing Final Project Solution

(Fitting) ISO 13482:2014 Standard Test

Walk Test

ER Requirements:

Safe Operation
Comfortable
Three Degrees of Freedom

Procedure:

Potential hazards of device Explained orally and written before device is donned by participant
Participant puts on prototype (Wears extended period)
3 degree of freedom are checked

Measurements:

ISO 13482:2014 standard for assistive robots
Potential hazards Disclosure
Device is enclosed
Comfortability Survey

Resources/Equipment:

Device
Lab Facilities
Participant

ER Requirements:

Safe Operation
Improved Walking Assistance
Comfortable
Within Budget

Procedure:

Potential hazards of device Explained orally and written before device is donned by participant
Participant don’s device
Participant walks 6 meters with device powered on and off

Measurements:

Toque provided while walking
Comfortability Survey

Resources/Equipment:

Device
Lab Facilities
Participant
Lab control Software

Sharon Toenjes

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NEMA 1 Test – Results

Weight of Device Between Procedures
Before Trial 1		After Trial 1		Before Trial2		After Trial 2
0.37kg	Device	0.37kg	Device	0.37kg	Device	0.37kg	Device
32g	Dirt	32g	Dirt	32 g	Dirt	31 g	Dirt

Device and dirt was weighed after each test
Scale measurement uncertainty +/-0.01g
No more than 2g of dirt entered the device
Brushes were effective in pushing out the dirt

Figure 24: Dirt Build Up from NEMA 1 Test

Table 4: NEMA 1 test data

Sharon Toenjes

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(Forward and backward motion)

(Lateral motion)

(Foot rotation)

Three degrees of Freedom Testing
Condition	Goal Angle	Measured Angle
Flexion/Extension	35°/15°	40 °
Abduction/Adduction	50°/15°	57°
Internal/External rotation	50°/15°	90°

Fitting (13482:2014 ) Test – Results

Table 4: Fitting test data

Figure 25: Fit Test Measurements

Sharon Toenjes

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Comfortability Survey

Is there any source of discomfort?
Did the device weigh you down?
Did the device interfere with range of motion?
Did protrusion interfere with normal motion?
On a scale of 1-10 rate comfort

Kyle Shough

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Budget Overview

Figure 26: Total Budget Overview

Kyle Shough

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Purchasing Bill of Materials

Table 5: Full BOM of all purchased items

Kyle Shough

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Future Work

Improve Waist belt

Increase rigidity to properly transmit load
More adjustable for different size waists

Reduce weight

Transition more components to carbon fiber

Refine manufacturing methods

Remanufacture slightly damaged pinion gears
Deface pulley hubs completely

Test metabolic consumption

Walk Testing
Thermal Testing
Measure oxygen intake necessary for exercise

Figure 26: Waist Belt

Jeff Yows

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Questions?

Jeff Yows