master thesis of Michele Folgheraiter, Politecnico di Milano

Transcription

1 master thesis of Michele Folgheraiter, Politecnico di Milano Seminario organizzato nell ambito del programma ENEA-MURST, progetto SIRO, da Giuseppina Gini

2 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.

3 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.

4 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

5 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

6 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, N force As a prosthetic device

7 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

8 Tendons: transmit the movements from muscles (in the forearm) to the different joints Superficial Flex 1 and 2 phalanx Flessors: Extensors flessors Deep flessors Flex 3 phalanx, then all the finger Extend all the phalanxes Adductors and abductors Adduct or abduct the first phananx Ligaments: elastic tissue around the jointsa.

9 OUR CONSTRUCTION To build the scheleton, nyloil, density g/cm3. Dimensions copied froma radiography. Joints copy the real ones. Giunto cilindrico Giunto sferico Ligaments are in rubber.

10 Tendons are steel under a silicone cover.

11 Prototype of a finger

12 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..

13 Pneumatic micro-cilinders 6 cilinders for each finger. For instance, blocking the second extensor and contracting the first flessor, we flect second and third phalanxes.

14 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.

15 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

16 CINEMATIC MODEL Sensors give the positions of cilinders, not of the phalanxes. We need the cinematic model for each finger.

17 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..

18 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.

19 Abilitazione riflesso miotatico Var=0 Miotatic reflex 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 Inibizione riflesso? Arresto del riflesso miotatico SI

20 Attivazione riflesso miotatico inverso Misurazione della Tensione nel tendine Invers miotatic reflex NO Tensione > T Ritardo di 0,3 sec SI Diminuire pressione nei cilindri NO Inibizione riflesso? SI Arresto del riflesso miotatico inverso.

21 HIERARCHY OF THE REFLEX CONTROLS Comands Sensory data Inibition Controllo ad Alto Livello Giunto Giunto Riflesso Miotatico Inverso Riflesso Miotatico

22 EXPERIMENTS ON THE PROTOTYPE Data acquisition card PCL-812. : - 16 analogical input. - 2 analogical output digital input digital output.

23 Index movement contract 1 Flessor Re1ease 1 Estensor

24 Flecting the first phalanx contract 2 Flessor release 2 Extensor Flecting second and third phalanxes Fix 2 Extensor release 1 Extensor contract 1 Flessor

25 Index abduction Contrac abductor Release adductor Index adduction Contract adductor Release abductor

26 3D MODEL Anatomic specifications Design choices Choices for the prototype Verifiche sul modverify on the modelello 3D

27 Cinematics verifications Hand closed thumb index opposition

28 movies Index flession Better extension after flession Another flession