WP4 Focused research on the octopus anatomy and biomechanicsIROS 2012 workshop on Metrics of sensory motor integration in robots and animals
Vilamoura, Portugal, October 12, 2012
Cecilia Laschi, Laura Margheri The BioRobotics Institute, Scuola Superiore Sant’Anna
Barbara Mazzolai Center for Micro-BioRobotics@SSSA
Italian Institute of Technology (IIT)
Quantitative measurements of Octopus vulgaris arms
for bioinspired soft robotics
No rigid structures:
all-direction bending
(same size of their brain capsule – Ex: 1-inch hole)
Variable and controllable stiffness
Manipulation and locomotion capabilities
Distributed control (50x106 neurons in each arm, more than in the brain)
Objectives: studying the octopus and building a
robotic octopus
Expected results:
octopus biomechanics, motor control,
arms, reach & grasp objects, squeeze
What is special in the octopus
The octopus muscular hydrostat
Where are insertions of longitudinal muscles?
How is it possible for the nervous tissue to be stretched and reach elongations
like the muscular or connective?
How much force are the arms capable of exert?
How much is the arm stiffness?
Need for quantitative data on the
octopus anatomy and biomechanics,
design of the octopus-like robot
Anatomy:
Artificial muscular hydrostat performance
Characterization of the octopus arm for biomimetics
Need for quantitative data on the
octopus anatomy and biomechanics,
design of the octopus-like robot
Anatomy:
Artificial muscular hydrostat performance
Characterization of the octopus arm for biomimetics
Non-invasive, destruction-free method
internal structures on anesthetized
rectangular tank
Linear transducer LA435 (at 18 MHz)
Axial-lateral resolution: 0.085-0.104 mm
Histology
Collaboration with Stazione
vivo the arms of Octopus vulgaris
&
Scanning of the Transverse, Sagittal and Horizontal planes
Direct measurement of anatomical structures dimensions
Measures of the
Geometrical features (I) L. Margheri, G. Ponte, B. Mazzolai, C.
Laschi, G. Fiorito 2011 Non invasive study
of the Octopus vulgaris arm morphology
using ultrasound. J. Exp. Biol. 214, 3727-
3731
Geometrical features (II)
Echo Intensity signal (EI):
and grey-scale analysis, using
standard histogram function
L. Margheri, G. Ponte, B. Mazzolai, C. Laschi, G. Fiorito 2011 Non invasive study of the Octopus vulgaris arm
morphology using ultrasound. J. Exp. Biol. 214, 3727-3731
Ultrasound investigation on moving animals
Ultrasound techniques can be applied as non-
invasive tool to investigate the arm structure
and the behavior of the arm-nerve cord in vivo.
A linear transducer (18 MHz) to examine the
arm in freely moving octopuses during
elongation/shortening, pulling and stiffening
moving octopus
Nerve Cord passive Elongation
arms to achieve large elongation without mechanical constraints
Shortened Arm Elongated Arm
3D Investigation of the Arm Morphology Ultrasound imaging and histology are applied to investigate arm
morphology along the three planes, with the research of muscles insertions, the observation of the muscular and nervous tissues arrangement, to reconstruct a 3D map of the arm. Arm Horizontal section in sonographic images
and corresponding histological sections Muscles insertions observed
on horizontal sections
Results on octopus arm anatomy
L. Margheri, C. Laschi, B. Mazzolai 2012 ‘Soft robotic arm inspired by the octopus. I. From biological
functions to artificial requirements’. Bioinspiration & Biomimetics, In Press
L. Margheri, G. Ponte, B. Mazzolai, C. Laschi, G. Fiorito, “Non-invasive study of Octopus vulgaris arm
morphology using ultrasound”, The Journal of Experimental Biology, Vol.214, 2011, pp.3727-3731.
Nerve cord: sinusoidal arrangement allows arms large elongation without
mechanical constraint
arm allow local bending
• Radial net configuration with straight interweaving of transverse muscle fibers
• Key-role of the trabeculae in maintaining circular the transverse section during contraction
Need for quantitative data on the
octopus anatomy and biomechanics,
design of the octopus-like robot
Anatomy:
Artificial muscular hydrostat performance
Characterization of the octopus arm for biomimetics
Two-synchronized High-Speed cameras (DALSA Falcon1.4M100) with
High-Resolution (1400Hx1024W @ 100 fps to 1400Hx200W @ 500 fps)
Falcon 1400 x 1024 @ 100 fps
Geometrical references on the external and internal walls of the tank
Reconstruction of the scene
Correction of optical reflection phenomena
Movement analysis and measurement of the octopus using anatomical markers (eyes, arm tip)
Geometrical references for scenes reconstruction
Stream5 Video Analysis SW
Methods: video setup and camera calibration
Design of the Instrumental setup Design of dedicated devices based on a graduated tube in transparent
Plexiglas and a supporting plate to measure one arm at a time, and
useful to create a collaborative interaction with the animal for the
acquisition of active measures
• Support the octopus positioning and perform the task
• Enable the octopus to use external handhold
• Assure that the measured values are referred only to the arm inside the tube
• Easily determine which arm is inside the tube and is used for the task
The tip of the tube can be sensorized (i.e. load cell)
with a purpose-made packaging anchored to the
opening of the tube
In Vivo Measurement of the Octopus Arm
Biomechanical Measurements
(dynamic, contr./relax phases)
‘Soft robotic arm inspired by the octopus. I.
From biological functions to artificial requirements’.
• B. Mazzolai, L. Margheri, M. Cianchetti, P. Dario, C. Laschi
‘Soft robotic arm inspired by the octopus. II.
From artificial requirements
Record the octopus with the
two stereo cameras during the
jet propulsion movements
tip, using the external and internal references
Speed record 100 fps
Kinematics movement analysis to define the central part of the
stereotyped trajectory (max acceleration)
model, considering the position of the plane of motion
Elongation Strain Measurement
Different Weight (140 ÷ 560g)
In vivo Measurement
(L) during elongation and the reference length (0) during
propulsion, normalized in respect to the reference length (0)
70 % of length variation (mean strain) corresponding to a
23% of diameter reduction in a cone with constant volume -50-40-30 -20-10 0 0
10 20 30 40 50 60 70 80 90
100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300
radius variation (%)
% )
R
RL
L
Setup validation and methods applicability on a large number of animals
Measures on arms used by each animal in performing the task
237 elongation movements
vs. Target distance
vs. Arm Length
Isometric Pulling Force:
Integrated force sensor
sex and weight)
494 + 434 measurements/subject
Method
(animal mass = 1600g, 494 measures)
Fiso(max): 26.8 N (R3) : 200 mm
(animal mass = 476g, 434 measures)
Time for task: 20-50 sec
Contraction time: 1-2 sec
Fiso(average,arm): 40 N (male)
used as end effector, while the
proximal part is used to exert forces.
Similar pattern as muscle fiber
• Fmax/Area = 7.9x104 N/m2
• Arm Stiffness during isometric contractions: Ktot (slope) = 1.87 x 102 N/m
Measurement of the arm rest length and total stiffness
Isometric Force Results (II)
• 0 = length at which maximum active contractile force is developed
• Rest length(length at which force is zero): rest= 0.34 0
Stiffness - Force with variable elastic loads
• F(t)
• Stiffness (stress-strain)
Study of the effects of different elastic loads on the contractions of octopus arm and measurement of stiffness in dynamic conditions
Method
tasks to measure the force capability in
different points along the arm
Force - displacement
K(arm) = 9.5 x 105 N/m2
(Elephant trunk = 106 N/m2, Wilson et al 1991)
Similar pattern as muscle fiber
Elongation :
70% of arms mean elongation corresponding to 23% of diameter reduction
Results on octopus biomechanics
(m=1600g) 28.6 N @ 200 mm
(m=476g)
Grasp Point Position
Contraction Time
1-2 sec
Stiffness
Max velocity 2 N/mm*s
The mechanical measurements of the octopus arm capabilities have been used in the model to obtain information about the arm visco-elastic properties and muscle activation function.
From characterization to modelling and simulation
Visco-elastic model for octopus arm
Force measurement in isometric condition Force measurement against elastic loads
isometric elastic loads
• Active component: • Elastic element of stiffness kp • Viscous element B • Active state element (contraction of muscle for each received stimulus)
contractile force C and rate constant β of exponential decay: activation function • Passive component:
• Elastic element of stiffness ki • External load:
• Elastic forces element of stiffness ke • gravitational mass M and viscosity D
Visco-elastic model for octopus arm
Linear visco-elastic model of muscle
Force generated by arm (input in the model):
Isometric contractions
isometric
Input: Isometric force F(t) (contr/relax) for different lengths
• Kp = 3.357 x 105 N/m
• Ki = 3.355 x 105 N/m
• B = 100 Nsec/m
• C = 10 N
• Kp = 3.357 x 105
• Ki = 3.355 x 105
Force measurement against elastic loads elastic
loads
The simulations with the model are in good
agreement with the experimental measurements
Biomechanics in octopus behavior
When interpreted in a behavioral context, the elongation efficiency reveals the potential for biomechanical influences on predation, exploring, or animal-animal interaction (mating).
The size or the sex of the animal may have an impact on the mechanical
efficiency, or different arms may show different performance
The instrumental setup used to measure the
mechanical capability of the arms to elongate and
reach a food target has been used on 19 animals
different for sex and size (12 males and 7
females, Dorsal Mantle Length range 72.5-
122.4mm, longest arm lengths range 320-565
mm) to investigate possible differences among
the 8 arms or different animals
Results from statistical analysis of measured elongations
Females achieved higher elongation percentages (75%, SD 26%) than males of a same size (61%, SD 33%, t-test, p<0.05). Difference is higher when comparing the arm R3 (hectocotylus in males), with 87% (SD 38%) for the females versus 54% (SD16) for the males
Smaller size octopuses achieved higher average elongation percentages (72%, SD 28%) than larger octopuses (63%, SD 32 %)
Mazzolai B.*, Margheri L.*, Dario P., Laschi C. Measurements of octopus arm elongation movement:
evidence of differences by animal sex and size. Journal of Marine Biology and Ecology.
Favorite arm use: octopuses preferentially
use L3 arm (longest arm)
First assessment of biomechanical quantification as a potential method
for the study of octopus behavior and differences among individuals.
OBJECTIVE Extracting bio-inspired criteria to develop innovative attachment/detachment mechanisms.
SUCKER INVESTIGATION
ULTRASOUND MRI HISTOLOGY CRYOSEM
INTERNAL STRUCTURE OF THE DENTICLES
DENTICLES AND NERVOUS STRUCTURES
LONGITUDINAL SECTION OF ARM AND
SUCKER
CENTER FOR MICRO-BIOROBOTICS IIT@SSSA
Sucker 3D reconstruction is most important in order to obtain the all spatial information necessary to address new biological knowledge and investigation, as for example: physical dimensions, morphological information, spatial arrangement of different tissues, etc.. Morever, 3D reconstruction is required to generate a surface mesh for later numerical processing.
Arm 3D from MRI Sucker 3D from Histology
Arm 3D from Histology Arm 3D from MRI Arm 3D from MRI
Arm 3D from MRI Arm 3D from MRI Sucker 3D from Histology
Arm 3D from Histology Arm 3D from MRI
WHY 3D RECONSTRUCTION?
Biological Results (Octopus vulgaris) Robotic Solution and Performance Measure method
Tr an
sv e
rs e
M u
sc le
70% of arm elongation corresponding to 23% of diameter reduction
Input to model for the design of SMA helical and define
In vivo biomechanical measurement (24
octopuses, 112 max elongations)
Mean Pulling Force
Time to contract -Longitudinal cables - Sheaths to reduce friction and avoid silicone damages - Calibration parameters (t,F)
In vivo biomechanical measurement (2
octopuses, 928 max of pulling force)
49.8N@400mm (m=1600g)
26.8N@200mm (M=467g)
1-2s
Grasp Point Position 0.75 of total arm length End effector position and active arm
length
Nerve Cord Arrangement
Sinusoidal arrangement at the arm rest length while has a distension during the elongation
Large elongations can be achieved using a sinusoidal arrangement for cables
Ultrasound (MyLabFiveVET@18MHz)
Design of transverse actuators inspired by the octopus muscles arrangement
• Radial net configuration with
maintaining circular the
transverse section during
More efficiency in the reduction of the diameter
4 arcs configuration: - too simplistic - not shape preserving - not bioinspired - lower efficiency
Radial configuration
Transverse Muscles: SMA springs
Transverse EI: 29.3±1.5
B. Mazzolai, L. Margheri, M. Cianchetti, P. Dario, C. Laschi ‘Soft robotic arm inspired by the octopus. II. From artificial requirements
to innovative technological solutions’. Bioinspiration & Biomimetics. In Press
Laschi, C., Cianchetti, M., Mazzolai, B., Margheri, L., Follador, M., Dario, P. (2012) A Soft Robot Arm Inspired by the
Octopus Adv. Robotics 26, 4
Measurements of the Active Strain of the Octopus Arm vs Artificial Arm
• 23% of diameter reduction has been used as specification input in the model for the design of the SMA helical to define:
- NiTi Alloy mechanical properties - Wire diameter
- Average spring diameter - Number of coils - Heat treatments
Transverse Muscles: SMA springs
• Measured 70% of arm
diameter reduction
B. Mazzolai, L. Margheri, M. Cianchetti, P. Dario, C. Laschi ‘Soft robotic arm inspired by the octopus. II. From artificial requirements
to innovative technological solutions’. Bioinspiration & Biomimetics. In Press
Laschi, C., Cianchetti, M., Mazzolai, B., Margheri, L., Follador, M., Dario, P. (2012) A Soft Robot Arm Inspired by the
Octopus Adv. Robotics 26, 4
Measurements of the pulling force applied by the octopus arm vs artificial arm performance
• Results of the force measurements (40 N mean, 1-2 sec contraction time) are used as specification in setting the longitudinal actuators of the robotic arm prototypes
• Cables have been covered with sheaths to reduce friction and avoid silicone damages
• The grasp point position at a 0.75 of total length has been used to allow grasping during the arm prototype pulling tests
Longitudinal Muscles: longitudinal cables + sheaths
B. Mazzolai, L. Margheri, M. Cianchetti, P. Dario, C. Laschi ‘Soft robotic arm inspired by the octopus. II. From artificial requirements
to innovative technological solutions’. Bioinspiration & Biomimetics. In Press
Laschi, C., Cianchetti, M., Mazzolai, B., Margheri, L., Follador, M., Dario, P. (2012) A Soft Robot Arm Inspired by the
Octopus Adv. Robotics 26, 4
Structural design specifications from octopus nerve cord arrangement
• Nervous tissue of the arm nerve cord has a sinusoidal arrangement at the arm rest length while is extended during elongation
• Large elongations can be
achieved using a sinusoidal
Shortened Arm Elongated Arm
B. Mazzolai, L. Margheri, M. Cianchetti, P. Dario, C. Laschi ‘Soft robotic arm inspired by the octopus. II. From artificial requirements
to innovative technological solutions’. Bioinspiration & Biomimetics. In Press
Laschi, C., Cianchetti, M., Mazzolai, B., Margheri, L., Follador, M., Dario, P. (2012) A Soft Robot Arm Inspired by the
Octopus Adv. Robotics 26, 4
• Muscles insertions along the arm
allow multiple point bending
• The arm prototype rely on additional cables from the base of
the arm and fitted to several points along the arm length,
thus improving bending capability
Longitudinal Muscles: longitudinal cables
multiple point bending
Design of longitudinal actuators inspired by the octopus muscles arrangement
B. Mazzolai, L. Margheri, M. Cianchetti, P. Dario, C. Laschi ‘Soft robotic arm inspired by the octopus. II. From artificial requirements
to innovative technological solutions’. Bioinspiration & Biomimetics. In Press
Laschi, C., Cianchetti, M., Mazzolai, B., Margheri, L., Follador, M., Dario, P. (2012) A Soft Robot Arm Inspired by the
Octopus Adv. Robotics 26, 4
Octopus-like arm mock-up
Simplified version of the longitudinal and transverse actuation system
Calisti M, Arienti A, Giannaccini M, Follador M, Giorelli M, Cianchetti M, Mazzolai
B, Laschi C and Dario P (2010) Study and fabrication of bioinspired octopus arm
mockups tested on a multipurpose platform IEEE/RAS-EMBS Int. Conf. on
Biomedical Robotics and Biomechatronics (BioRob 2010), Tokyo, Japan.
Design of an artificial muscular hydrostat
• Longitudinal muscles • Transverse muscles • External connective tissue • Central nerve cord channel
C. Laschi, B. Mazzolai, V. Mattoli, M. Cianchetti, P. Dario, “Design of a biomimetic robotic octopus arm”,
Bioinspiration & Biomimetics, Vol.4, No.1, 2009
• Longitudinal cables • Transverse SMA springs • External braid • Central electric wires • Sensorized skin with suckers
Cianchetti M, Arienti A, Follador M, Mazzolai B, Dario P and Laschi C “Design concept and validation of a
robotic arm inspired by the octopus” Materials Science and Engineering: C, Vol.31, 2011, pp.1230-1239.
PATENT PENDING
SMA (Shape Memory Alloy)
Water environment which facilitates
SMA (Shape Memory Alloy) spring
SMA spring with a PTFE sheath in distilled water coupled with
silicone parallelepiped 25x10x5 mm that provides a restoring force
•12 coils
• thermally insulated with a shrinkable PTFE sheath
•1.2 A of activation current
Development of the mechanical interface between the soft actuator and the muscular unit
First transverse section mock-up
• <D>/d = 6 (cycle life parameter)
• Spring internal diameter = 1 mm
Silicone / braided sleeve:
• External diameter = 28mm
• Internal diameter = 20mm
1 second of 600 mA direct current and then 50% duty cycle pulse current
Octopus-like robot arm
12 transverse actuators, 8 SMA springs each, uniformly
distributed along the arm
P h o to
actuation
12 transverse actuators, 8 SMA springs
each, uniformly distributed along the arm
Bending Elongation
Mather J A, 1998
Though the octopus arms are not specialized and they all can perform the same functions, they are used more often for: - pair 1: reaching, fetching, grasping, sensing; - pair 2: crawling, elongation, shortening; - pairs 3 and 4: crawling and standing
The robotic octopus works in water and
its buoyancy is close to neutral.
based on the
The sensorized skin covers the arms
Multi-arm robotic octopus prototype
Conclusions • In biomimetics / bioinspired robotics, biology gives specifications for the
design work • Descriptions and models available in biology literature may be insufficient for
this role • Additional quantitative data may be needed, measured with the robotics
perspective and objectives • Example of translation of biological measures into robotics specifications • The first prototypes represent a good translation of biology into robotics
Thanks
SSSA OCTOPUS Team: • Paolo Dario • Barbara Mazzolai • Matteo Cianchetti • Laura Margheri • Andrea Arienti • Maurizio Follador • Marcello Calisti • Michele Giorelli • Federico Renda • Francesco Giorgio Serchi • Alessia Licofonte • Ilaria Baldoli • …our octopuses www.octopus-project.eu
Acknowledgments to: European Commission in the ICT-FET OCTOPUS Integrating Project, #231608