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Super-Elastic Continuum Robot for Endoscopic Articulation and Manipulation
(SCREAM)
Zach Boyer, Cory Brolliar, Ben Mart, Kevin O’Brien
Advisors: Prof. Loris Fichera, Prof. Gregory Fischer, Prof. Ken StaffordAssisting: Alex Chiluisa
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Clinical Significance● Several diseases exist that affect the larynx● 20,000 people in the U.S. have RRP
(Recurrent Respiratory Papillomatosis) ● Patients require procedures often (about 100
per lifetime)○ Expensive and inconvenient, requiring general
anesthesia
● Estimates suggest the lifetime treatment costs somewhere between $60,000 - $470,000
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Vocal Folds
Current In -Off i c e L a r y n gea l S u r ger y
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Technical Limitations of Current T ec h n i qu es
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● Certain areas require the endoscope to be placed in a way that the laser cannot be seen by the camera
● Current procedure requires the physician to move the endoscope
Amplify manipulation and visualization c a pa bi l i t i es of ph y s i c i a n s du r i n g en dos c opi c pr oc edu r es t o t r ea t v oc a l di s ea s es
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Our Project Goal:
Requirements and ConstraintsThe instrument must:
● Bend with a small radius of curvature● Have articulation controlled from outside the endoscope● Be smaller than 1.8 mm in diameter● Must have an inner diameter of at least 1 mm to allow a
laser waveguide to pass through it
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Control Body
InsertionTube Bending
Section
InstrumentChannel Inlet
Small Scale Continuum Robots ● Superelastic tubes (Nickel-Titanium) which can be
controllably translated, rotated and bent● Enable dexterity in very small diameters (potentially
as small as a needle)● Have a hollow lumen that can be used to pass
instruments
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Swaney et al, JMD 2017
Webster et al. T-RO 2010
Determining Preferred Robot Design
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Determining Preferred Robot Design● Modeled one and two link model where each link had constant curvature● Used a Rapidly-expanding Random Tree search algorithm to determine the
reachable workspace and access to tissue
91 Link Model 2 Link Model
Simulation Results: Reachable Volume
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Conclusions: Both reach approximately the same volumePyriform sinuses more reachable with 2 Links
Vocal Folds
1 Link 2 Link
Simulation Results: Surface Area
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Conclusions: Both reach approximately the same areaPyriform sinuses more visible with 2 Links
Vocal Folds
1 Link 2 Link
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To use a single notched link
Our Decision
How many notches?
● Reran previous MatLab simulation with a new kinematic model
● Model reflected notched one link robot
● Tested four, five, and six notch designs
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Visible Area of Notched Tubes
1417.86 cm2 19.06 cm2 18.15 cm2
Vocal Folds
Vocal Folds
Design Overview● Three components● Augmented manual control● Integrated sensing● Sensing and Control
Modularity
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Transfer tube
End effector
Transmission Module
Laser Fiber
The End Effector
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● Made of 1.8 mm outer diameter Nitinol
● Actuated with Nitinol wire● Must be able to pass through the
working channel when bent● Disposable
Laser Fiber
The Transfer Tube
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Desiderata:
● Rigid to transfer torque and translation
● Compliant to pass through endoscope
● Smaller than 1.8 mm● Disposable● Currently looking at
Nasogastric tubes
Transmission Overview
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Absolute Encoder
Rotation
Advancement
TendonDisplacement
4.7”
3.5”
Visualizing the End Effectorhttps://users.wpi.edu/~kobrien2/scream/
● Transmission loss when bending laser○ Will conduct tests to determine transmission loss given curvature
● Warn user if they are near the limits of the manipulator
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Moving Forward into C -T er m
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Milestone DeadlineManufacturing and assembly January 31
Testing and validation February 18
Calibration February 3
Test in plastic throat February 4
Test in anthhropomorphic model February 10
Visualization verification with EM tracker
February 15
Thank you!Questions or comments?
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Contact us at: [email protected] thanks: Dr. Thomas L. Carroll
Otolaryngologist at Brigham and Women’s Hospital
Backup
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Detailed timeline (1 of 3)
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Milestone DeadlineManufacturing and assembly
Procurement of components January 10
Transmission assembly January 20
Electrical assembly (wire up the potentiometers, etc.)
January 20
Manufacturing of the distal section (NiTi tube machining, coupling with transmission tube)
January 25
Integration January 31
Detailed timeline (2 of 3)
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Milestone Deadline Success criterionTesting and validation
Kinematic Calibration February 3 Device can travel linearly at least 25 mm and bend at least XX degrees (see results of simulations)
Initial testing in anthropomorphic model
February 10 Device can reach the undersurface of the vocal folds
Deployment tests through operating channel (we can use a flexible rubber tube to this purpose)
February 15 Device fits through the operating channel of an endoscope
Sensing of device bending February 28 We can track the instrument bending with
Detailed timeline (3 of 3)
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Milestone DeadlinePresentation and reporting
Testing with the physician (will use a likert-scale questionnaire to collect his feedback on the device and inform the design of the next iteration)
March 15
Final project report March 20
Project video (to be disseminated on youtube)
March 31
Project presentation day
Backup
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Backup
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Backup
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Backup
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Backup
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Backup
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Nitinol Slides
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Tendon Force = 3N
Two Unique Characteristics: 1) Super-elasticity
0.2% 6.0%
Stre
ss
Strain
Nitinol
Stainless Steel
…and it’s:Biocompatible, MR conditional,Kink resistant, Corrosion resistant,Fatigue resistant!
What is nitinol?50 Ni / 50 Ti (Atomic Percent)Intermetallic CompoundVery little solubilityHigh heat of formationDisorders upon melting
Accidental discovery 1959: NiTiNaval Ordinance Lab• While developing missile nose
cone materials and hiding from his ex wife
Crystal Defects
Nitinol vs. “Traditional” MetalsTraditional Metal Crystal Structure: • BCC, FCC, HCP • Structure changes due to chemistry, heat
treatment
0.2%
Stre
ss
Strain• With strain greater than 0.2%
deformation occurs by dislocation motion and is not reversible
• Crystal structure does not change but defects accumulate
Nitinol Phase Transformation –Results in Unique Characteristics
NiTi: Two Ways to Create Phase Transformation
• Stress Induced Phase Transformation - Apply Force• Stretch the crystals to move relative atom position• Stress Induced Martensite (SIM)• Release allows spring back (reversible)
Reversible Process
Load
NoLoad
Austenite
MartensitePermanent Set6.0%
Stre
ss
Strain
Superelastic
Austenite to Martensite
Martensite to Austenite
NiTi: Two Ways to Cause Phase Transformation
Hot(Austenite)
Cold(Martensite)
Apply Heat for Thermodynamic Drive to Change Crystal Structure
Exploiting Nitinol:How do we use thermal shape memory?
Cool
Heat
Not as easy …Phase change and property change but no outward impact
Austenite Martensite_____________________________
Melting Point (°C) 1310 N/AElastic Modulus (GPa) 75 45Electrical Resistivity (µΩ-cm) 86 76Thermal Expansion (10-6/°C) 11 6.6Thermal Conductivity (W/m-°C) 18 16.3Heat Capacity (cal/g-°C) 0.07 0.07
What determines if NiTi is Superelastic or Thermal Shape Memory?
Transformation Temperature • Very sensitive to ingot chemistry• 1% change in Ni can shift Af by 100°C
• Increasing Ni lowers Af
• 50.8 at% Ni is typically for medical• Difficult to accurately measure and control ingot-
to-ingot variations !
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25 C25 C
Thermal Shape Memory
Super-elastic
Tran
sfor
mat
ion
Tem
pera
ture
°C
Why is transformation temperature important?
Af =TTest
Stress induced martensite forms
Test @ 37 °C - Change Af Temperature Af > TTest
Applied stress deforms martensite … heating above Af can
recovery shape
Af = 37 CAf = 45 C
Af = 25 C Af = 10 C Af = -10 C
Af < TTest
Stress needed to form martensite increases
with decreasing AfLower Af Temperature → Stiffer NiTi
Why is test temperature important?
Stress needed to stabilize martensite
increases with temperature
Constant Af = 5 °C
Test @ Various Temperatures
NiTi Stiffness Increases
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What can change transformation temperature? NiTi (50.8 Ni)
Chemistry Heat Treatment
Device Heat TreatmentDuring heat treatment:• Ni-rich precipitates form
• Ni4Ti3, Ni3Ti2, Ni3Ti• Lowers Ni-content of the matrix• Shift Af upwards
• Lowers load and unload plateaus
Sub-micron Precipitate Particles
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Wrought Nitinol Production: Tube & SheetTubing:• Start with solid bar ~ 5/8 inch round by 5
feet• Gun drill hole along length• Draw through die multiple steps• Insert mandrel
• Hard or Deformable• Draw down similar to wire• Remove mandrel
• Proprietary techniques to withdraw mandrel
• Intermediate anneals to soften• Acid etching to clean and remove oxide• Approximately 70 step process• FNA Needle Tube
• ~ $15 per foot
Sheet:• Start with square bar and cold roll to size • Similar cold work / anneal sequences
Part 3: Device Fabrication
Subtitle - I have a wire, tube or sheet … Now what?
Device Fabrication
• Shape the raw material• Centerless Grind• Machine, Drill, EDM, etc• Laser cut• Laser weld
• Heat treat to set final form and develop desired properties• Chemical process to finish surface
• Etch• Passivate• Chemical process to finish surface
• Etch, electro-polish, passivate• Polymer coat
Device Heat Treatment
• Precise temperature is critical
• Activates the shape memory or superelastic behaviour • If not already straight annealed
• Sets the shape of the product • Fixturing and constraint during
heat treatment.
• Controls transformation temperature and therefore mechanical
ti
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30
30
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Device Heat Treatment
• Longer times/higher temperatures provide better shape retention
• 450°C to 530°C : typically 500°C, 5-30 mins• Residual cold work needed to maintain strength/plateau levels
• Complex interaction of cold work, precipitation and annealing
• Several Ni-based precipitate chemistries, each with a different effect• Under heating limits shape retention … Over heating decreases
stiffness and limits elastic recovery
Practical Implications
• Shape setting very sensitive to temperature changes
• Robust durations at approx 500°C
• More sensitive to time variation above/below this
• Also balances residual cold work and annealing
• Processes with rapid heat up preferred
• Avoids multiple effects from different regimes
• Better process control• Fluidized baths preferred to
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Af before heat treatment 11°C[Pelton, 2000]
Laser welding
Local temperature increase creates a molten pool of liquid metalWhen heat is removed liquid solidifies from outside edge to centerInert gas cover is required to prevent oxidation and inclusionsGeometry is important re-solidified metal is notch sensitive
Fabrication: Machining
• Traditional Machining is possible but challenging
• Material may smear creating subsurface damage
• Grinding can cause heating and changes in material properties
Summary
Weld Depth: 61 umNitinol: an Enabling Technology for Medical Devices• Superelastic performance• Thermal Shape memory performance• Biocompatible• MR conditional• Kink resistant• Corrosion resistant• Fatigue resistant• Weldable