Transcript Sample Poster 2

Powered Arm Orthosis to Augment Arm
Function in Persons with Disabilities
Daniel Abramovich
Michael Scarsella
Steven Toddes
Advisor: Professor Allen Hoffman | Mechanical Engineering Department
Overview
Mechanical Analysis
Duchenne’s Muscular Dystrophy (DMD) is a degenerative genetic disease occurring
primarily in adolescent males. DMD results in a deterioration of muscle tissue causing
afflicted persons to be wheelchair bound. Those afflicted with DMD typically lose muscle
function in their limbs proximally to distally, leaving them with only minor tactile function in
their hands by their teenage years, resulting in limited independence. Patients will
generally require assistance in completing activities of daily living (ADL’s), such as brushing
teeth, fork feeding, and combing hair. Orthotic devices have helped DMD patients regain
small levels of independence by helping to recreate movements within their arms. By
designing a powered arm orthosis with a comprehensive control system, DMD patients could
operate a mechanism that would allow them to complete ADL’s with minimal assistance,
thereby restoring their independence.
Prior to manufacturing, stress analyses were conducted to ensure the prevention of failure
under the maximum loading conditions. A Finite Element Analysis was performed on the
elbow joint sprocket and other critical components to see how they would perform under the
maximum loading conditions. Stress calculations on the elbow flexion worm determined the
relationship between safety factor and applied torque on the worm under maximum loading.
Humeral Rotation
Torque on Elbow Flexion Worm vs. Safety Factor
30
25
Safety Factor
Torque vs. Safety Factor
Abstract
Safety Limit
15
Safety Factor for Maximum
Loading Condition on
System
10
5
Muscular Dystrophy, and other similar afflictions, where articulation of arm muscles is
hindered, can severely impact the quality of life. By creating a wearable,
electromechanically powered arm orthosis, strength no longer available to the arm muscles
is augmented and controlled by the user, thereby restoring arm function. In the design
produced, a wearable orthosis controlled by joystick allowed the user to lift his own arm plus
an additional 3 lbs in weight. The device incorporated 2 degrees of freedom or DOF (elbow
flexion and humeral rotation) that can be controlled independently or simultaneously.
With the use of the powered orthosis, daily tasks were achieved at a rate that was only 70%
slower than that of a normally functioning person.
Elbow Flexion
0
0
20
40
60
80
Torque in N*m
Final Design
Results
1.
Succeeded in powered, 2 - DOF motion in both independent and coupled motion.
Humeral Rotation:
95°
Elbow Flexion:
110°
2.
Prototype Load Capacity vs. Original Task Specifications:
Humeral rotation :
166% Elbow flexion :
120%
Project Objectives
Load Test
The goal of this project was to develop and build a powered arm orthosis for clients with
symptoms of or similar to Muscular Dystrophy, in order to aid in tasks of daily living;
improving independence and quality of life. To obtain the desired level of quality, the design
would have to meet specifications in the following categories:
●Safety
●Functionality
Humeral Rotation
Elbow Flexion
1.6
1.4
Current Drawn (Amp)
●Comfort
●Ease of use
20
●Aesthetics
●Durability
Final Design
Prototype
1.2
1
0.8
0.6
0.4
0.2
0
0
User Controls
1
2
3
4
5
6
External Load (lb)
With the feature of coupled motion, the device achieved a 41% speed increase in
motions that would be completed by each degree of freedom independently.
ADL's
4.
Orthosis weighs 5.2 lb, a 48% improvement
in weight reduction over previous design.
18
16
14
12
10
8
Trial #2
4
Trial #1
2
Activity
• Lighten design by use of more lightweight materials that do not compromise strength or
structural integrity
• Lighter/Higher torque motors for increased power and lighter overall design weight
• Adjustable humeral bars to fit a wider range of clientele
• Condensed circuitry for increased portability
Humeral Rotation
Subassembly
Trial #1
Trial #2
Normal
0
Recommendations
Frame
Subassembly
Normal
6
washing face
Time (s)
blow nose
Activities of Daily Living (brushing teeth,
combing hair, drinking, blowing nose,
washing face) completed at a rate of only
70% slower than that of a normally
functioning person.
drink cup
5.
Comb hair
The orthosis is controlled by the user through a joystick interface, and is powered by a 12 volt
source. The joystick control works by sending a signal through a dual H-bridge circuit, which
drives the intended motor in the appropriate direction through polarity switching. The
electronics are neatly arranged within a box with connections for the joystick, power cables to
the 12 volt source, motor cables, as well as a battery meter display for protection in the event
that the orthosis is being run by a portable battery source.
3.
Toothbrush
The orthosis consists of three subassemblies: frame, elbow flexion, and humeral
rotation. The frame provides rigid support to the user’s arm and allows for fluid motions in
each degree of freedom. The elbow flexion subassembly utilizes a gear train assembly,
driven by a DC motor, which applies a torque to a sprocket that is affixed to the forearm
portion of the frame. By driving the motor in either direction, the forearm portion of the
frame articulates up or down. The gearing system amplifies the motor’s torque by 54x and
incorporates an inline slip clutch. The humeral rotation subassembly includes a circular
track around the upper arm, which creates humeral rotation by rotating the frame and lower
arm, while stabilizing the upper arm. The humeral rotation is driven by a bevel gear set and
a worm which translates circumferentially around the circular track on a custom delrin
slider.
Elbow Flexion
Subassembly
Special Thanks: Gary and Andy of the Massachusetts Hospital School
Control System