Super-Elastic Continuum Robot for Endoscopic Articulation ... · Super-Elastic Continuum Robot for...

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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

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

Vocal Folds

Current In -Off i c e L a r y n gea l S u r ger y

Technical Limitations of Current T ec h n i qu es

● 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

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

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

Swaney et al, JMD 2017

Webster et al. T-RO 2010

Determining Preferred Robot Design

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

Conclusions: Both reach approximately the same volumePyriform sinuses more reachable with 2 Links

Vocal Folds

1 Link 2 Link

Simulation Results: Surface Area

Conclusions: Both reach approximately the same areaPyriform sinuses more visible with 2 Links

Vocal Folds

1 Link 2 Link

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

Visible Area of Notched Tubes

1417.86 cm2 19.06 cm2 18.15 cm2

Vocal Folds

Design Overview● Three components● Augmented manual control● Integrated sensing● Sensing and Control

Modularity

Transfer tube

End effector

Transmission Module

Laser Fiber

The End Effector

● 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

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

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

Moving Forward into C -T er m

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?

Contact us at: screamteam@wpi.eduSpecial thanks: Dr. Thomas L. Carroll

Otolaryngologist at Brigham and Women’s Hospital

Backup

Detailed timeline (1 of 3)

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

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

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

Nitinol Slides

Tendon Force = 3N

Two Unique Characteristics: 1) Super-elasticity

0.2% 6.0%

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

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

NoLoad

Austenite

MartensitePermanent Set6.0%

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?

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 !

25 C25 C

Thermal Shape Memory

Super-elastic

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

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

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

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

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

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