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Redundant Design and Adaptive Control of an Interleaved Continuum Rigid Manipulator
—Ben Conrad
University of Wisconsin-Madison
2016/11/21
Academics:
o Undergraduate (B.S) at UW-Madison in Engineering Mechanics – Astronautics
o Graduate Degrees: M.S. and Ph.D – pending – UW Madison
Publications:1. Conrad, B., Zinn, M., “Interleaved Continuum-Rigid Manipulation: An Approach to Increase the
Capability of Minimally-Invasive Surgical System”, ASME/IEEE Transactions on Mechatronics,
Accepted TMECH-02-2016-5178.R1
2. Conrad, B., Zinn, M., “Estimating Cardiac Catheter Performance Requirements”, ASEM Journal ofMedical Devices (submitted – via DMDC 2017).
3. Conrad, B., Zinn*, M.R., "Closed Loop Task Space Control of an Interleaved Continuum-RigidManipulator ", IEEE International Conference of Robotics and Automation, 26-30 May 2015,Seattle, WA, pp 1743 - 1750, (acceptance rate: 35%).
4. Conrad, B.L., Zinn, M.R., "Interleaved Continuum-Rigid Manipulation Approach: Developmentand Functional Evaluation of a Clinical Scale Manipulator", Intelligent Robots and Systems (IROS2014), 2014 IEEE/RSJ International Conference on, pp. 4290-4296, Chicago, IL.
5. Conrad, B.L., Jung, J., Penning, R.S., Zinn, M.R., "Interleaved Continuum-Rigid Manipulation: AnAugmented Approach For Robotic Minimally-Invasive Flexible Catheter-based Procedures", IEEEInternational Conference on Robotics and Automation, Karlsruhe, Germany, May 6-10, 2013(refereed proceedings: acceptance rate 35%).
Research and work experience including
o Summer internships at NASA Kennedy Space Center, TracLABS (mobile robotics)
and VytronUS (robotic catheters)
o Flew ZeroG twice with Prof. Shedd
o LaVision in Germany (with Prof Sanders) - Built hyperspectral lasers
o REACH Lab – Catheter / Interleaved Robotics
Wisconsin has been a great experience…3
youtube.com/watch?v=oiXgWG9ASMc
PhD research motivated by cardiac catheters4
We have a 3+ DOF manipulator Constructed from biosafe,nonlinear materials
Subject to unknownmechanical constraints Operating in a highly
dynamic environment
~5 mm/cycle
Guided by limited-resolution sensors Ablating tissue with
unknown material properties
Performing a procedure whose efficacy cannot be immediately determined
Skilled surgeons overcome many of these,but a fundamentally limited system...
Consider the fundamental physics…
An elastomer structureo stiffness similar to organs inherent safety
Underactuated and highly hysteretico leads to limit cyclingo static models ok, dynamic insufficient
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increasingarticulation
Safety limits performance…
80beats/min = 1.3Hzo heartbeat not sinusoidal
Bandwidth of ~2Hz Teleoperation wants ~20Hz
can we decouple safety and task performance?
Let’s complement catheters with rigid joints6
A new concept, let’s be strategic
Desire increased
…to enableo Teleoperationo Obstacle avoidanceo Avoidance of distal dynamicso Target motion compensationo Contact impedance managing…among others
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5D Actuation &Control Prototype
Performance: Increase accuracy, precision, & speed?
Reduce or avoid nonlinearities?
Dexterity: Expand the dexterous workspace?
Maintain ‘good’ configurations?
1DPerformance
Testbed
1 degree of freedom: 4x faster, same accuracy8
Summarizing the performance testbed
Desire increased
Other takeaways:o Frequency partitioning attractiveo Joint limits are importanto Plant dynamics change with articulation
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5D Actuation &Control Prototype
Performance: Increase accuracy, precision, & speed?
→ 4 times faster, same accuracy
→ CL fundamentally limited by first mode
Reduce or avoid nonlinearities?
→ Fine resolution from rigid joints
Dexterity: Expand the dexterous workspace?
Maintain ‘good’ configurations?
A 5D clinically-approximate manipulator
The moving parts…
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Ex-vivo Drives Vasculature Model
5 DOF Interleaved Manipulator
5D design – degrees of freedom
2 flexible segments
o Proximal roll and catheter
2 rigid joints
o Distal pitch and roll
o Rigid joints 3D printed
1 virtual tip-to-target distance
Redundancy varies with configuration
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Pitch Axis
Distal RollAxis
Base Roll Axis
ArticulationAngle
Pitch Angle
Tip-to-TargetDistance
5D design – actuators and transmissions
Remote actuation
o Servos external to the patient
Flexible transmissions safely
navigate vasculature
o 12mm Teflon proximal tube
o SS driveshafts Ø0.64 x 894mm
o Shafts and tendon separated
by smaller tubes
o No distal joint encoders…
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Tendon
5D design – sectioned joints
Large, local reductions
o 700:1, reduces driveshaft windup
Miniature bearings on rigid axes
Cable transmissions (0.15mm diameter Kevlar)
Catheter tendon decoupled from rigid joints
o 0.23 mm, Teflon-coated
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AblationProbe
CatheterTendon
Ø12mm
58mm = 2.2”
Improvements since the preliminary
Rebuilt distal joints with much less compliance
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An adaptive controller
Error formed in the task space
Inverse kinematics fully specified, found using Subplex alg.
xPC servocontroller with >30Hz drive bandwidth
Kinematic parameters estimated from prior motions
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Tracking tasks look like
The target moves in a 3D shape, tip & target move by turns
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~150mm
Tip emfsensor
Target emf sensor
First, the open loop:
As-measured kinematics
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unlearned, openunlearned, closed
Closing the loop
As-measured kinematics
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unlearned, openunlearned, closed
Locally adapting kinematic parameters
Want to capture nonlinearities distributed in task space
Space divided between buckets
Each bucket estimates the kinematics for trajectories within
o NLOpt, Subplex: https://github.com/bc0n/ICRMKinematics
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Open loop
With learned kinematics
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unlearned, openunlearned, closedlearned, open
Closed loop
With learned kinematics
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unlearned, openunlearned, closedlearned, openlearned, closed
Live tracking summary
Learned open loop MORE accurate than closed loop..
..depends on trajectory speed
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Closed loop is desirable for absolute accuracy
Previously moving in a highly repetitive fashion,
some learning was path-dependent
Non-repetitive learning and
point-to-point motion require
closed loop control
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What have we actually learned?24
This work has been described in
Interleaved continuum rigid manipulation: An augmented..
o Conrad, Jung, Penning, and Zinn, IEEE ICRA, 2013
Interleaved continuum-rigid manipulation approach..
o Conrad and Zinn, IEEE IROS, 2014
Closed loop task space control of an interleaved…
o Conrad and Zinn, IEEE ICRA, 2015
Interleaved Continuum-Rigid Manipulation: An Approach..
o Conrad and Zinn, Mechatronics, forthcoming
Adaptive Closed Loop Control of an Interleaved…
o Conrad and Zinn, in prep
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Summarizing the systems
Desire increased
Other takeaways:o Performance sensitive to rigid joint compliance
o Controller validation challenging, lengthy
o Functional design --2-3x clinical scale
o Hasn’t broken over 2000+ runs
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Performance: Increase accuracy, precision, & speed?
→ 4 times faster, same accuracy (1dof)
→ CL fundamentally limited by noncollocated sensor and 1st mode
→ OL enables accuracy & speed
Reduce or avoid nonlinearities?
→ Fine resolution from rigid joints
→ Spatial easier, smaller than temporal
Dexterity: Expand the dexterous workspace?
→ Redundant design and control
Maintain ‘good’ configurations?
→ Optimization IK permits weighting
→ Bucket quality metric
Towards a clinical device…27
http://w.namiki.net/product/kbo/dc/15motor.html
5D design very conservative
Max clinical OD of ~4mm:
o 5D scaled by gearhead Ф6 1.5mm?
Towards a clinical device…28
Many new actuator concepts
Increasing ability to assemble at the micro scale
2mm
I’m headed to the Schnitzer Lab
Senior ME at Howard Hughes Medical Institute / Stanford
They need systems like this fly manipulator, a Senior ME
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Questions?
Thanks to
o Mike Zinn
o Committee
o Lab mates
Supported by NSF grant IIS-1316271
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