1. MURI Biomimetic Robots Low-Level High-Level Control Control
Fabrication
11/14/2018

2. Low-Level Control MURI Comparison with Artificial Muscles
High-Level
Control
Comparison with Artificial Muscles
MURI
New Results on Measurements of Muscles
Fabrication
Gecko foot adhesion
Discussion of low level mechanism
11/14/2018

3. MURI Year Two Meeting2000 Professor Robert J. Full Daniel Dudek
Low-Level
Control
Professor Robert J. Full
Daniel Dudek
Dr. Kenneth Meijer
High-Level
Control
MURI
Basic properties of natural muscle
First direct comparison of natural muscle to artificial muscle
Fabrication
Diverse roles of muscles
11/14/2018

4. SDM permits embedded sensors and actuators
Manufactured Legs
SDM permits embedded sensors and actuators
What properties should legs possess? Why?
What properties should the actuators possess?
How many actuators should there be?
How should the actuators be controlled?
11/14/2018

5. MURI MURI Interactions Rapid Prototyping Stanford Muscles and
Motor Control
&
Learning
Locomotion
UC Berkeley
Johns Hopkins
MURI
Robot & Leg Mechanisms
Manipulation
Harvard
UC Berkeley
Sensors / MEMS
Stanford
11/14/2018

6. Interdisciplinary Collaboration
Proteomics
Metabolic Pathways
Actin/Myosin
Ion Channels
CPG
Ion Channels
Biomaterials
Neurosciences
Biointerfaces
BioMechanics
General Biological Principles
Novel Hypotheses & Devices
Biological Inspiration
General Robot Design Principles
Nanotechnology
SDM
Control Theory
Mechanics
Kinematics
Dynamics
Stability
Constitutive Relations
Circuit Theory
Mat. Science
11/14/2018

7. Road Map 1. What muscles can do. (Traditional characterization)
2. What muscles do in nature. (Inputs values from behavior)
3. Compare natural muscles to artificial muscles.
11/14/2018

8. Road Map 1. What muscles can do. (Traditional characterization)
2. What muscles do in nature. (Inputs values from behavior)
3. Compare natural muscles to artificial muscles.
11/14/2018

9. Muscle Model Activation Force Active force generating element
Passive visco-elastic element
Force
Time
Force
Activation
Based on the observation the contribution of the passive properties is so large the question becomes what is the role of the passive properties. The possibility exists that the passive muscles provide the animal with postural stiffness, whereas active muscles provide the stiffness necessary stable execution of locomotory tasks.
Based on the experimental observations a visco-elastic model is proposed to further study the contribution of the muscles to the stability of the overall system. The current tasks are: Characterize this model such that it can accurately predict stiffness values during different locomotor tasks (find parameter values).
11/14/2018

10. Activation
Human
Stimulation
(EMG)
Muscle Force
Cockroach
11/14/2018

11. Activation Force (mN) Maximum isometric stress 7 - 803 kN/m2 or kPa
Time to Peak Force: sec; 200-fold variation Time to 50% Relaxation: sec; 100-fold variation
600
Maximum isometric stress
kN/m2 or kPa
100-fold variation
Insect leg muscle
500
400 5 4
Force (mN) 3
300 2
200 1
100 20 40 60 80
100
Time (msec)
11/14/2018

12. Muscle Model Activation Force Active force generating element
Passive visco-elastic element
Force
Time
Force
Activation
Based on the observation the contribution of the passive properties is so large the question becomes what is the role of the passive properties. The possibility exists that the passive muscles provide the animal with postural stiffness, whereas active muscles provide the stiffness necessary stable execution of locomotory tasks.
Based on the experimental observations a visco-elastic model is proposed to further study the contribution of the muscles to the stability of the overall system. The current tasks are: Characterize this model such that it can accurately predict stiffness values during different locomotor tasks (find parameter values).
Force
Length
11/14/2018

13. Force-Length Curve Insect leg muscle Stress N/cm2 Strain
-0.2
-0.1
0.1
0.2
0.3 5 10 15 20
Strain
Stress N/cm2
Insect leg muscle
Maximum isometric stress varies with Strain
Animals tend to operate on the Ascending or Plateau region.
11/14/2018

14. Force-Length Variation20 40 60 80
100
-0.2
-0.4
0.4
0.2
Bee
Flight
Frog
Locust
Leech
Crayfish
Fly
larvae
Maximum Strain varies from %
100-fold variation
Relative Stress (%)
R. J. Full
Handbook of
Comparative Physiology
Strain
11/14/2018

15. Muscle Model Activation Force Active force generating element
Passive visco-elastic element
Force
Time
Force
Activation
Based on the observation the contribution of the passive properties is so large the question becomes what is the role of the passive properties. The possibility exists that the passive muscles provide the animal with postural stiffness, whereas active muscles provide the stiffness necessary stable execution of locomotory tasks.
Based on the experimental observations a visco-elastic model is proposed to further study the contribution of the muscles to the stability of the overall system. The current tasks are: Characterize this model such that it can accurately predict stiffness values during different locomotor tasks (find parameter values).
Force
Length
Force
Velocity
11/14/2018

16. Normalized Force (F/Fo)
Force-Velocity Curve
0.2
0.4
0.6
0.8 1 2 3 4 5 6
Relative Velocity (L s-1)
Normalized Force (F/Fo)
Insect leg muscle
Maximum Contraction Velocity
l/sec
60-fold variation
11/14/2018

17. Force-Velocity Curve Trade-off between Force and Velocity
Similar Shape of Curve
11/14/2018

18. Instantaneous Muscle Power
Maximum Instantaneous Power Output at 1/3 Maximum Contraction Velocity
Power = Force X Velocity
Power
Muscle
Force
Muscle Velocity
11/14/2018

19. Instantaneous Muscle Power
Maximum Instantaneous Power Output > 500 W/kg muscle S p e c i s V m a x ( L n g t h / ) F o k N 2 P W R E D 1 3 9 5 M u l 7 8 z r d f b 4 6 K y w T C
11/14/2018

20. Road Map 1. What muscles can do. (Traditional characterization)
2. What muscles do in nature. (Inputs values from behavior)
3. Compare natural muscles to artificial muscles.
11/14/2018

21. Muscles Activated Rhythmically at a Given Phase
In Vivo Activation
Muscles Activated Rhythmically at a Given Phase
ONE SECOND
200 MSEC
(Pearson, 1976)
CAT
COCKROACH
FLEXORS
EXTENSORS
GROUND CONTACT
PERIOD
COXA
FEMUR
11/14/2018

22. Full, 1997 Handbook of Comparative Physiology
Cycle Frequency
1000
Mosquitoes F l i e r s
Flies
Flower flies
Bees, Wasps
100
Aphids,
White flies
Crane flies
Beetles H z
Frequency <1 to 1000 Hz
Dragonflies
Sphinx moths
Butterflies
Saturnid moths 10 R u n n e r s S w i m m e r s
Invertebrates
Full, 1997 Handbook of Comparative Physiology 1 10 m g
0.1 mg
1 mg
10 mg
0.1 g
1 g
10 g
0.1 kg
1 kg
Body mass
11/14/2018

23. Muscle Lever Control Stimulation Stimulation - pattern - magnitude
- phase
Servo and
Strain
Force
- pattern
- magnitude
Transducer
Frequency
11/14/2018

24. Workloop Technique
Lever
11/14/2018

25. Workloop Technique Strain Stress Net Work per Cycle Work Output during1 2 3
Net Work
per Cycle
Work Output during
Shortening
Work Input to
Lengthen
Strain
Stress
11/14/2018

26. Power Generation 9-284 W/kg
Muscles as Motors
Power Generation W/kg t2 t3 t4 t5 t1 t 1 2 5 4 3
Force
Length
Scallop Swimming Muscle
Bird Flight Muscle
11/14/2018

27. Shape depends on Frequency
Workloop Shape
Shape depends on Frequency
Stress
Strain
Ellipsoid
Rectangular
Triangular
High >60Hz
Intermediate Hz
Low <30 Hz
11/14/2018

28. Work per cycle decreases with Frequency
Power vs Frequency
Power (W/kg)
0.1 1 10
100
1000
Work per cycle
(J/kg)
Frequency (Hz)
Work per cycle decreases with Frequency
Power constant
Scallop
Bee
11/14/2018

29. Stress, Strain vs Frequency
Frequency (Hz)
Strain (%)
Stress (kN/m ) 2
0.1 1 10
100
1000
Strain rate (L/sec)
Stress and Strain decrease with Frequency
11/14/2018

30. Road Map 1. What muscles can do. (Traditional characterization)
2. What muscles do in nature. (Inputs values from behavior)
3. Compare natural muscles to artificial muscles.
11/14/2018

31. Artificial Muscle? First Direct Comparison by K. Meijer Collaboration
Artificial Butterfly
Collaboration
S. V. Shastri R. Kornbluh R. Pelrine
Acrylic Dielectric Elastomer
SRI research engineer Roy Kornbluh
11/14/2018

32. Dielectric Elastomer Actuators
Polymer film
Compliant electrodes (on top and bottom surfaces)
Voltage off V
Voltage on
Soft ElectroActive Polymers (EAP)
Polymer film is sandwiched between compliant electrodes and acts as a dielectric (insulator).
Incompressible polymer gets thicker and contracts in area when a voltage is turned off.
Basic functional element
11/14/2018

33. Activation EAP has Rapid Kinetics Acrylic dielectric elastomer20 40 60 80
100
200
300
400
500
600
Force (mN)
Insect leg muscle 1 2 3 4 5 6
Time (msec) 20 40 60 80
100
600
700
800
900
1000
1100
1200
Time (msec)
Force (mN)
Acrylic dielectric elastomer
5 kV
4 kV
3 kV
2 kV
1 kV
stimulation
11/14/2018

34. Force-Length Curve EAP has a linear Force-Length Curve
-0.2
-0.1
0.1
0.2
0.3 5 10 15 20
Strain
Stress N/cm2
Insect leg muscle
0.05
0.1
0.15
0.2
100
120
140
160
180
200
Strain
Stress N/cm2
Acrylic dielectric elastomer
11/14/2018

35. Acrylic Dielectric Elastomer
Same Apparatus used to test Natural Muscle
Force
Dlength
46.2 mg at a 1 N pre-tension
Dimensions of active part of the actuator (l x w x h) x x 0.07 mm.
11/14/2018

36. Power Output EAP Produced and Absorbed Energy 5% Stress (Ncm-2)
100 50
150
-2.5
2.5 5%
Stress (Ncm-2)
Locomotion cycle %
Strain %
11/14/2018

37. EAP Power Output
As in Muscle, EAPs only Produce Power over a Particular Range of Strains and Stimulation Phases
11/14/2018

38. Work per Cycle Lower than mean Activation not Maximal
Work vs Frequency
0.1 1 10
100
1000
Work per cycle
(J/kg)
Frequency (Hz)
Work per Cycle Lower than mean
Activation not Maximal
EAP
11/14/2018

39. Stress, Strain vs Frequency
Frequency (Hz)
Strain (%)
Stress (kN/m ) 2
0.1 1 10
100
1000
EAP
Stress higher and Strain lower than mean.
11/14/2018

40. Power Output Comparison1 10
100
1000
Frequency (Hz)
Power
output
(W/kg)
Bee
Rat
Lizard
Crab
EAP
EAP within Range of Natural Muscle
11/14/2018

41. Conclusions 1. Muscles have a broad range of potential function.
2. Matching natural inputs required to reveal function
3. Can not refute EAP as artifical muscle
11/14/2018

42. MURI Year Two Meeting2000 Professor Robert J. Full Dr. Anna Ahn
Low-Level
Control
Professor Robert J. Full
Dr. Anna Ahn
Dr. Kenneth Meijer
High-Level
Control
MURI
Basic properties of natural muscle
First direct comparison of natural muscle to artificial muscle
Fabrication
Diverse roles of muscles
11/14/2018

43. Multiple Muscle Systems
Complex, Redundant? or
Diverse Functional Capacity?
11/14/2018

44. Questions Why are there so many muscles operating at a single joint?
Are all muscles created equal?
Can differences in function be explained by neural activation alone?
Can differences in function be explained by traditional characterizations?
Are muscles mainly power generators?
11/14/2018

45. Hypotheses Muscles of the same anatomical group
activated at the same time
will function similarly.
Two leg extensors acting at the same joint
activated during leg extension will
function similarly and both produce power.
Muscles of the same anatomical group, or synergists, activated at the same time will function similarly.
For example, two leg extensor muscles acting at the same joint activated at the beginning of leg extension will function similarly and both produce power.
11/14/2018

46. Two extensor muscles innervated by a single motor neuron
coxa-femur
joint
muscle 179
stance phase
joint extension
muscle shortening
muscles are both extensors of the coxa-femur joint of the cockroach.
muscles are both innervated by the same motor neuron.
both muscles are single motor unit muscles
small joint angle
long muscle lengths
large joint angle
short muscle lengths
Anna Ahn
11/14/2018

47. Hypothesis: Muscles stimulated by the same motor neuron function similarly.
NEURAL CONTROL
Stimulation patterns the same?
INTRINSIC MUSCLE PROPERTIES
Force-Length properties similar?
Force-Velocity properties similar?
Twitch kinetics similar?
Shortening deactivation similar?
11/14/2018

48. Stimulate motor neuron, while measuring EMG’s from 178 and 179.
(mean ± S.D.)
11/14/2018

49. Hypothesis: Muscles stimulated by the same motor neuron function similarly.
NEURAL CONTROL
Stimulation patterns the same? YES
INTRINSIC MUSCLE PROPERTIES
Force-Length properties similar?
Force-Velocity properties similar?
Twitch kinetics similar?
Shortening deactivation similar?
11/14/2018

50. Similar force-length properties
178
179
11/14/2018

51. Hypothesis: Muscles stimulated by the same motor neuron function similarly.
NEURAL CONTROL
Stimulation patterns the same? YES
INTRINSIC MUSCLE PROPERTIES
Force-Length properties similar? YES
Force-Velocity properties similar?
Twitch kinetics similar?
Shortening deactivation similar?
11/14/2018

52. Similar force-velocity properties
0.2
0.4
0.6
0.8 1 2 3 4 5 6
Relative Velocity (L s-1)
Normalized
Force
(F/Fo)
max. in vivo
velocity during running
178
179
11/14/2018

53. Hypothesis: Muscles stimulated by the same motor neuron function similarly.
NEURAL CONTROL
Stimulation patterns the same? YES
INTRINSIC MUSCLE PROPERTIES
Force-Length properties similar? YES
Force-Velocity properties similar? YES
Twitch kinetics similar?
Shortening deactivation similar?
11/14/2018

54. Similar isometric contraction kinetics
178
179
11/14/2018

55. Hypothesis: Muscles stimulated by the same motor neuron function similarly.
NEURAL CONTROL
Stimulation patterns the same? YES
INTRINSIC MUSCLE PROPERTIES
Force-Length properties similar? YES
Force-Velocity properties similar? YES
Twitch kinetics similar? YES
Shortening deactivation similar?
11/14/2018

56. Similar shortening deactivation
178
179
(mean ± S.D.)
11/14/2018

57. Hypothesis: Muscles stimulated by the same motor neuron function similarly.
NEURAL CONTROL
Stimulation patterns the same?
INTRINSIC MUSCLE PROPERTIES
Force-Length properties similar?
Force-Velocity properties similar?
Twitch kinetics similar?
Shortening deactivation similar? YES
11/14/2018

58. Muscle Power during Running
Two extensor muscles at same joint stimulated by the SAME neuron have different function.
Stiffening Element
Damper or brake
3 W kg-2
-19 W kg-2
= stimulation
11/14/2018

59. What’s different?
11/14/2018

60. Active force during shortening
178
179
stance
stance
= stimulation
11/14/2018

61. Conclusions
1. Muscle function cannot be predicted from neural activity.
Muscles innervated by the same motor neuron do NOT necessarily function similarly.
2. Muscles of the same anatomical group (178 and 179) can have many similar intrinsic muscle properties, but still function differently.
3. History-dependent properties may play an important role in determining muscle function.
11/14/2018

62. Implications for Robotics
1. Direct copying of the musculoskeletal system is likely to fail.
Muscle have diverse roles that can only be revealed by extensive experimentation.
2. Control and energy management may be attained using actuators with different properties rather than sending out complex control signals.
3. EAPs with muscle-like properties are available. More direct comparison are needed. More emphasis on function in devices required.
11/14/2018

63. Robotic Applications of EAPs
Second DOF
Leg actuator based on a stretched film actuator
Modular design composed of individual stretched film actuators integrated into a 6-legged walking robot
CAD representation of the robot including a second degree of freedom
11/14/2018