Anthromorphic Underactuated Hand with 15 Joints M E S R O B 2 0 1 - PowerPoint PPT Presentation

Anthromorphic Underactuated Hand with 15 Joints M E S R O B 2 0 1 5 A U T H O R S : E . M A T H E S O N , Y . A O U S T I N , E . L E C A R P E N T I E R , A . L E O N , J . P E R R I N T H A N K S T O B E N J A M I N G A U T I E R F O R T H E V I D E O . Matheson et al, 8-10 June MESROB 2015 1

CONTENTS 2  Introduction  Underactuated Systems  Mechanical Model  Simulation  Conclusion Matheson et al, 8-10 June MESROB 2015 2

INTRODUCTION 3  What are prosthetic devices?  Replaces missing or injured part of the body  Why do we need them?  Perform everyday tasks, regain independence  Ability to work, ability to interact socially  What are the main challenges involved?  Replicating human motion  Producing natural control – the human body is a vastly superior system to any we have in robotics Matheson et al, 8-10 June MESROB 2015 3

INTRODUCTION 4  Development of a prosthetic hand  Similar to human hand size  Ability to grasp different objects – natural conformity  Simplicity of movements for control  Challenges  Complexity of a human hand: 20 DOF in the fingers and thumb alone, 19 muscles, 17 joints, 20 bones  Potential Solution  Underactuated mechanism: less Picture courtesy of AIST [11] actuators than independent joint variables Matheson et al, 8-10 June MESROB 2015 4

INTRODUCTION 5  IRCCyN Hand  4 fingers, 1 thumb  15 DOF  6 Motors  Flexion and extension motion only for fingers and thumb  Supination and Pronation for the thumb  Design and construction by Alpes Instruments, Grenoble Matheson et al, 8-10 June MESROB 2015 5

UNDERACTUATED SYSTEMS 6  Performance Metrics: Grasping Ability  Determined by the mechanical design: however, the design process is not well understood for underactuation  Control during grasping is limited – a simulation is necessary to understand the behaviour during grasping  Grasp-stability metric: Contact Forces  Positiveness: All contact forces must be positive (compressive)  Distribution: Isotropic force applications – each contact point applies an equal force  Magnitude: Different criteria such as minimum or maximum allowable contact force in any configuration  Resultant Direction: Designing the contact force to be in a specific direction e.g. Toward the palm Matheson et al, 8-10 June MESROB 2015 6

UNDERACTUATED SYSTEMS 7  Mechanical methods of achieving underactuation  Differential mechanisms  Self locking mechanisms  Compliant mechanisms  Benefits  Intrinsically conform to the shape of the object  Less actuators = lower cost, mass and profile  Robust to collisions Matheson et al, 8-10 June MESROB 2015 7

MODEL: Transmission System 8  Cable / Pulley (flexion) and spring (extension) transmission system  Pulleys are free to rotate – introducing compliance Matheson et al, 8-10 June MESROB 2015 8

MODEL: Joint Structure 9  Finger: Thumb: Hand:  3 revolute joints 3 revolute joints 15 joints  Axes all parallel 1 perpendicular, 2 parallel Tree-structure Matheson et al, 8-10 June MESROB 2015 9

Model: Finger Motion 10  Effect of the pulley radii  Finger radii:  With tuning: [0.004, 0.0035, 0.003] • [0.001, 0.003, 0.004]  Thumb radii:  With tuning: [0.004, 0.0025]; [0.001, 0.004] Matheson et al, 8-10 June MESROB 2015 10

MODEL: Workspace 11  The workspace can be increased by solving an optimisation of design parameters (e.g. Pulley radii) Matheson et al, 8-10 June MESROB 2015 11

MODEL: Force Analysis 12  When is an underactuated system stable? -At static equilibrium. “A grasp is stable if and only if the finger is in static equilibrium ” -Birglen et al. (2008) [1]  The phalanges in contact with an object have a positive (or zero) corresponding contact forces. Matheson et al, 8-10 June MESROB 2015 12

MODEL: Contact Force 13  i) Ideal Grasping Sequence  ii) Ejection sequence (Birglen et al.[1]) Matheson et al, 8-10 June MESROB 2015 13

MODEL: Contact Force (Birglen et al) 14  Analysis of whether an under-actuated finger is able to generate an external wrench onto a fixed object  Defines two matrices - completely describe the relationship between the input torque of the finger actuator and the contact forces on the phalanges  First we correlate input and output virtual power of the kinostatic system Matheson et al, 8-10 June MESROB 2015 14

MODEL: Contact Force (Birglen et al) 15 Matheson et al, 8-10 June MESROB 2015 15

MODEL: Contact Force (Birglen et al) 16  Compare input and output virtual work τ   a   τ = τ = − ∆ θ K   2 2 2   τ = − ∆ θ   K 3 3 3  τ - input torque vector (actuator and springs)  ω – vector of angular joint velocities  ξ i – twist of i th contact point on i th phalanx  ζ i – wrench of i th contact point on i th phalanx  K i – stiffness of spring at joint i Matheson et al, 8-10 June MESROB 2015 16

MODEL: Contact Force (Birglen et al) 17  Assumptions  One contact point on each phalanx  Contact force is in the plane  Only revolute joints present ◦ ω i – angular vel. of i th phalanx ω     f i   ti ◦ v i – linear vel. in x, y at i th   ξ = ς = x v f     i i i i contact point   τ   y     v ◦ f ti – tangential force i i ◦ f i – normal force ◦ τ i – torque applied by i th phalanx Matheson et al, 8-10 June MESROB 2015 17

MODEL: Contact Force (Birglen method) 18  T – depends on transmission mechanism used to propagate actuation torque to the phalanges . θ = T ω a  r 1,2 are the radii of pulleys at joints 2 and 3   1 0   = r T T − 1 1   thumb   r 2 Matheson et al, 8-10 June MESROB 2015 18

MODEL: Contact Force (Birglen method) 19  Forces at the contact point  Here, τ is torque applied at each joint (originally from the motor and then that from the springs/ geometric setup)  Note: for the thumb, force is planar (just from flexion/ extension) rather than spatial (a component from pronation/ supination).  Singularities in J or T will lead to cases where no contact forces can be produced. Matheson et al, 8-10 June MESROB 2015 19

SIMULATION 20  Two Point Contacts  Single Point Contact  Finger, Phalanx 1 Contact Force:  Finger , Phalanx 3 Contact 35.3254 Force: 18.75  Finger, Phalanx 3 Contact Force:  Thumb, Phalanx 3 Contact 18.75 Force: 1.9948  Thumb, Phalanx 3 Contact Force: -6.3827 Matheson et al, 8-10 June MESROB 2015 20

SIMULATION 21  Three Point Contact  Finger, Phalanx 1 Force: 24.1233  Finger, Phalanx 2 Contact Force: 17.5636  Finger, Phalanx 3 Contact Force: 18.75  No contact with the thumb Matheson et al, 8-10 June MESROB 2015 21

SIMULATION 22  Non-homogenous object  Finger 1, Phalanx 1 Contact Force: 32.88  Finger 1, Phalanx 2 Contact Force: -24.37  Finger 1, Phalanx 3 Contact Force: 18.75  Finger 2, Phalanx 3 Contact Force: 18.75  Finger 3, Phalanx 3 Contact Force: 18.75  Finger 4, Phalanx 1 Contact Force: 34.61  Finger 4, Phalanx 2 Contact Force: -27.09  Finger 4, Phalanx 3 Contact Force: 18.75  No contact with the thumb Matheson et al, 8-10 June MESROB 2015 22

CONCLUSION 23  Underactuated prosthetic hands show valuable promise as useful and efficient tools for patients in the future  Simulation of this hand in Matlab shows adequate contact forces can be generated for cylindrical objects weighing less than 0.5 kg Matheson et al, 8-10 June MESROB 2015 23

Perspectives 24  Control these hand with signal of the nervous central system.  An on-line intramuscular EMG (iEMG) decomposition was proposed with a Markov Model.  From the excitation signal to the input actuator: A muscle model. A matrix moment. Matheson et al, 8-10 June MESROB 2015 24

Perspectives 25 Matheson et al, 8-10 June MESROB 2015 25