master thesis of Michele Folgheraiter, Politecnico di Milano
Seminario organizzato nell’ambito del programma ENEA-MURST, progetto SIRO, da Giuseppina Gini
INTRODUCTION
•The human hand has been well studied in biology and medicine.
•In engineering no real duplications of the human hand have been
developed; most of the projects aim at reproducing some functionalities
for prosthetic devices or for industrial grasping.
In this project we start from biology and we try to develop a solution
as much natural as possible.
AIMS
Why to build an artificial hand resembilng the human hand?:
•as a prosthetic device. The artificial hands now available are
very simple a do not guarantee complex movements..
•As the hand for a humanoid robot. The next development of
robotics will provide robots able to cope with the human
abilities.
SOME PREVIOUS EXAMPLES OF HANDS
Some examples
:
JPL-Standford Hand (1985)
•Tre fingers with 3dof each
•Pneumatic actuators
•Belgrade/USC hand I (1988)
•Five fingers with 1dof
•Electric actuation
Utah /MIT hand (1986)
•Four fingers with 4dof
•Pneumatic actuation with tendons
•Sensors.
•Omni hand 2 (NASA 1998)
•Three fingers and 10dof
•Part of a humanoid robot
DLR hand (1997)
•Four fingers, 3 dof each
•Electrical microcilinders
•11N max force
•25 sensors in each finger
•SUMA hand
•Two fingers, 1dof each
•Electrical actuation, 0-100 N force
•As a prosthetic device
ANATOMY
• Bones are divided in 3 parts:
Falangi
Metacarpo
Carpo
5° Metacarpo
4° Metacarpo
3° Metacarpo
2° Metacarpo
1° Metacarpo
•Enartrosis, 3/4 sphere (2dof) and trocoids (1dof).
Trocoide
Enartrosi
•Tendons: transmit the movements from muscles (in the forearm) to the
different joints
Superficial
• Flessors:
Flex 1 and 2 phalanx
flessors
Deep
flessors
•Extensors
•Adductors and abductors
Flex 3 phalanx, then all the
finger
Extend all the phalanxes
Adduct or abduct the first
phananx
•Ligaments: elastic tissue around the jointsa.
OUR CONSTRUCTION
To build the scheleton, nyloil, density 1.125 g/cm3.
Dimensions copied froma radiography.
Joints copy the real ones.
Giunto cilindrico
Ligaments are in rubber.
Giunto sferico
Tendons are steel under a silicone cover.
Prototype of a finger
ACTUATION SYSTEM
Muscles are made of many
fibers, with two components in
series and in parallel.
Contraction
is
given
by
miofibrille, elasticity by tendons
and connectives.
Artificial muscle:
Small, light, able to exert forces 500g to 20 Kg..
Pneumatic micro-cilinders
6 cilinders
finger.
for
each
For instance, blocking the
second extensor and
contracting
the
first
flessor, we flect second
and third phalanxes.
In each movement, at least two tendons are actuated through a couple of
cilinders.
The cilinder connected to the flexor has a camera with air, and the second
with oil, to get a better precision.
Five electrovalves open and close.
SENSORY SYSTEM
Receptors in the hand converts informastion from the external world into
electric pulses for the nervous system.
In
the
muscles,
neuromuscolar fibers (in
parallel) are sensible to the
elongation, Golgi organs, (in
series with tendons) to
streching.
In the joints, Ruffini terminations are sensible to movement and velocity, etc...
Sensors in the artificial hand: now only the basic ones: position, tension,
contact
CINEMATIC MODEL
Sensors give the positions of cilinders, not of the phalanxes. We need the
cinematic model for each finger.
Given P in the 3 reference systeml S3, we build P in S0:
To obtain the relation between the position of tendons and the joint angles,
we use:
.
We need the relation between the position of the tip and the S3 system; this
is found through experiments.
.
CONTROL SYSTEM
This is a typical dynamic, non-linear, multivariate system. A traditional
control system will be very difficult.
In the nervous systeml however we find two levels:
•the encephalon, which integrates the sensory data and decides the control,
• the spinal system responsible of the reflex control.
We developed 2 algorithms able to imitate the miotatic and inverse
miotatic reflexes.
Abilitazione
Abilitazione riflesso
riflesso
miotatico
miotatico
Miotatic reflex
Var=0
Lettura posizione
del giunto p1
Ritardo di 0,3 sec
Lettura posizione
del giunto p2
Var=Var+(p1-p2)
NO
Var > VAR
SI
NO
Movimento del
giunto di -VAR
Var=0
Arresto
Arresto del
del
riflesso
riflesso
miotatico
miotatico
Inibizione
riflesso?
SI
Attivazione
Attivazione riflesso
riflesso
miotatico
miotatico inverso
inverso
Invers miotatic
reflex
Misurazione della
Tensione nel tendine
SI
Diminuire
pressione nei
cilindri
Tensione > T
NO
Ritardo di 0,3 sec
NO
SI
Inibizione
riflesso?
Arresto
Arresto del
del riflesso
riflesso
miotatico
miotatico inverso.
inverso.
HIERARCHY OF THE REFLEX CONTROLS
Comands
Sensory data
Inibition
Riflesso
Miotatico
Inverso
o
Giiuunntto
G
Controllo ad
Alto
Livello
Riflesso
Miotatico
EXPERIMENTS ON THE PROTOTYPE
Data acquisition card PCL-812. :
- 16 analogical input.
- 2 analogical output.
- 16 digital input.
- 16 digital output.
Index movement
•contract 1° Flessor
•Re1ease 1° Estensor
Flecting the first phalanx
•contract 2° Flessor
•release 2° Extensor
Flecting second and third
phalanxes
•Fix 2° Extensor
•release 1° Extensor
•contract 1° Flessor
Index abduction
•Contrac abductor
•Release adductor
Index adduction
•Contract adductor
•Release abductor
3D MODEL
Anatomic
specifications
Choices for the
prototype
Design choices
Verifiche sul
modverify on the
modelello 3D
Cinematics verifications
Hand closed
thumb index
opposition
movies
Index flession
Better extension after flession
Another flession