towards stiffness sensors for minimally invasive …...towards stiffness sensors for minimally...
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Towards Stiffness Sensorsfor Minimally Invasive Surgery
Dr. Angela Faragasso
Service Robotics LaboratoryDepartment of Precision Engineering
The University of Tokyo
ICRA 2017 Workshop on Innovative Haptic InterfacesEmerging from Soft Robotics
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Outline• Motivation
• Vision-based Stiffness Sensing Mechanism
• Multi-directional Stiffness Sensor for Medical Palpation
• Clip-on Stiffness Sensor for Endoscopic Camera
• Conclusion
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• Tactile information is crucial in the early stage of diagnosis;
• The outcomes of manual palpation procedures are subjective and limited to the area reachable with the human hands;
• An objective in-vivo measurement technique for assessing the material properties of soft tissue is still missing and will definitely be a valuable tool in diagnosing pathologies.
Motivation
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Haptic Haptic or kinesthetic communication recreates the sense of touch by applying forces, vibrations,
or motions to the user.
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Research Problem
Soft tissue stiffness estimationAim
Development of a stiffness sensing
mechanismApproach
Stiffness estimation as function of contact forces
Sensing Principle
Vision-based estimation of contact forcesTechnique
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Vision-based Force Sensor
Mechanical Principle
The distance between the sphere and the camera varies with the interaction force.
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Mathematical Model
A mathematical model computes the force as a function of the
feature’s radius.𝐹𝐹 𝑟𝑟 = 𝐾𝐾∆𝑥𝑥 = 𝑘𝑘 𝑥𝑥0(1 − 𝑟𝑟0
𝑟𝑟)
Vision-based Force Sensor
* Faragasso A. et al. “Novel uniaxial force sensor based on visual information for minimally invasive surgery", ICRA, 2014.
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Vision-based Stiffness Sensor
Mechanical Principle
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Mathematical Model
Vision-based Stiffness Sensor
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Stiffness Estimation of Silicon Phantoms
Vision-based Stiffness Sensor
*Faragasso A. et al. “Endoscopic Add-on Stiffness Probe for Real-time Soft Surface Characterisation in MIS", EMBC, 2014.
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Sensor Design
Multidirectional Stiffness Sensor
for Medical Palpation
It comprises four differentsprings (three soft ones and
one that is stiffer).
The displacement of theindenters varies when
interacting with a soft object.
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Mechanical Principle
Multidirectional Stiffness Sensor
for Medical Palpation
• A mechanism that couples the indenter movements with themovements of spherical features in front of the camera;• The movements of the features in the image plane ∆(x), canbe used to estimate the movements of the indenters.
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Evaluation Test with Silicon Samples
Multidirectional Stiffness Sensor
for Medical Palpation
Stiffness evaluation of four different silicon materials
*A. Faragasso et al. “Multi-Axis Stiffness Sensing Device for Medical Palpation", IROS, 2015.
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Sensor Design
• Finite Element of Analysis;
• A calibration device isused to evaluate resolutionand force range.
Clip-on Stiffness
Sensor for Endoscopic
Camera
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Simulation & Calibration Results
Clip-on Stiffness
Sensor for Endoscopic
Camera
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Image Processing
Clip-on Stiffness
Sensor for Endoscopic
Camera
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Evaluation Test Results
Clip-on Stiffness
Sensor for Endoscopic
Camera
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Conclusion• Development of a sensory mechanism
that uses deformable elements and vision to compute forces;
• Real-time stiffness estimation as a function of the relative forces inferred from the deformation of elastic element under load;
• Robust estimation of soft tissue stiffness at different angles.