DEVIEW DAY1. mit cheetah 로봇의 탄생

1. MIT Cheetah 로봇의 탄생
석상옥
Naver Labs

2. contents
1. Introduction
2. Leg Actuation System Design
3. Parallel Processing in Mobile Robot Controllers
4. Design Principles for Energy Efficient Legged Locomotion
5. What’s Next?

3. 1.
Introduction

4. 1. Introduction
http://www.youtube.com/watch?v=KYKg9-T2eNU
2012 BMW 3 Series Production - BMW Munich Plant - Body Shop
BMW 3 Series Production Boston Dynamics Atlas
Manufacturing Robot vs. Mobile Robot

5. 1.1 Running
[1] P. WEYAND et al., “Faster top running speeds are achieved
with greater ground forces not more rapid leg movements”, J. A
ppl. Physiol. 89: 1991–1999, 2000
𝐹𝑧(N)
𝑇
𝑡 𝑠 𝑡 𝑠 𝑡 𝑎𝑡 𝑎
M=70 kg
V=4.5 m/s
700N
𝐹𝑧(𝑡) ⅆ𝑡 = 𝑚𝑔𝑇
𝑇
0
Vertical Momentum Conservation

6. 1.2 In the Blink of an Eye
Airbag: 30ms
Playback speed: 0.06x
MIT Cheetah running at 6m/s
• Swing time: 250ms
• Stance time: 57ms
Blink: 400ms

7. 1.3 Requirements
• Ground reaction force at 6m/s:
– Maximum: 450N
– Stance time: 57ms
• Leg actuation system’s force bandwidth:
– 120Hz (MIT Cheetah’s real spec)
• Main controller’s control sampling frequency:
– 20~30x of the closed loop bandwidth [64]
– 2.4-3.6kHz
– At 4 kHz, sampling period is 250𝜇𝑠
Fy
57ms
Touchdown
angle

8. 2.
Leg Actuation System
Design
Seok, Sangok, et al. "Actuator design for high force proprioceptive control in fast legged locomotion." Intelligent Robots and Systems (IROS),
2012 IEEE/RSJ International Conference on. IEEE, 2012.

9. 2.1EM Motors
Recommended
operation range
Short-term
operation range
Torque
Angular speed
Maximum
Continuous
Torque/Current
Demagnetization
Torque/Current
10X of max. cont.
Torque/Current
V= Vrecommended
𝑟
𝑡
𝑙
𝑟 : gap radius
𝑡 : rotor thickness
𝑙 : rotor length
Stator
Rotor
Torque Density ∝ 𝑟

10. 2.2 Force Control
Geared Motor with
Torque(Force) Sensor
Leg
Motor
High Gear Ratio
Transmission
Stiff
Sensor
Series Elastic Actuator
Leg
Spring,
Encoder
Motor
High Gear Ratio
Transmission

11. 2.3 High Force Proprioceptive Actuation
High Torque
Density Motor
Low Gear Ratio
Transmission
Low Inertia
Leg
No Force (Torque) Sensor
No Series Elastic
Proprioceptive Actuation:
Collocated force control through
(1) maximizing torque density
(2) minimizing mechanical impedance

12. 2.4 Impedance Control
0
50
100
150
200
250
Time(ms)
4000 50 100 150 200 250 300 350
Force(N)
k=5,000N/m, d=100Ns/m
Commanded
Force Sensor
5cm
Force
Sensor
Sorbothane
Foot

13. 3.
Parallel Processing in
Mobile Robot
Controllers
A Highly Parallelized Control System Platform Architecture using Multicore CPU and FPGA for Multi-DoF Robots
Sangok Seok, Dong Jin Hyun, SangIn Park, David Otten, and Sangbae Kim
Submitted: 2014 IEEE International Conference on Robotics and Automation (ICRA)

14. 3.1 Importance of Fast Processing
MIT Cheetah: 12 DoF
Asimo: 34 DoF
More Functions (More Actuators and Sensors)
More Agile (Higher System Bandwidth)

15. 3.2 Solutions
Faster system:
- Faster Bus
- Faster CPU [66],[67]
Main Controller
Fast CPU
Distributed
Controller 1
⋮
Distributed
Controller 2
Distributed
Controller N
Main Controller
Multicore CPU, FPGA
Distributed
Controller 1
⋮
Distributed
Controller 2
Distributed
Controller N
Fast BUS
Parallel connection
Parallel Processing:
- Parallel connection
- Multicore CPU, FPGA

16. 3.3 Parallel Processing
Single Worker:
1. Task Parallelism
Wash IronDry
4h 5h 6h
Dish Vacuum Cook
1h 2h 3h
Wash IronDry
1h 2h 3h
Worker 1:
Worker 2:
Worker 3:
Vacuum
Cook
Dish
4h 1h 2h 3h
Vacuum
Cook
Dish
4h
Wash
Iron
Dry
Vacuum
Cook
Dish
Wash
Iron
Dry
Wash
Dry
Iron
Vacuum
Cook
Dish
5h 6h
= 6 Tasks, 6 Hour
= 6 Tasks, 4 Hour = 6 Tasks, 1 Hour
Worker 1:
Worker 2:
Worker 3:
Worker 4:
Worker 5:
Worker 6:
2. Pipelining
Independent Dependent

17. 3.4 Processing Sequence in MIT Cheetah
Forward
Kinematics
Running
Algorithm
PD Control Jacobian
Current
Commands
Receive
Sensor Data
Distributed
Controller 1
Distributed
Controller 2
Distributed
Controller N
Main Controller
⋮
IndependentProcess
Dependent Process

18. 3.5 Overall Process
Current 1
Current 2
:
Current n
Current
Current
Current
Communication
Output Emulator
Motor Driver 1
Motor Driver 2
.
.
.
Motor Driver n
.
.
.
Angle
Current
Angle
Current
Angle
Current
Communication
Input Emulator
Angle 1
Angle 2
:
Angle n
Current 1
Current 2
:
Current n
Front Left Leg
Front Right Leg
Rear Left Leg
Rear Right Leg
Kinematics
.
.
.
𝑇1 = 17.24𝜇𝑠 𝑇2 = 22𝜇𝑠 𝑇3 = 50𝜇𝑠 𝑇4 = 44𝜇𝑠 𝑇5 = 36.85𝜇𝑠

19. 3.6 Overall Process
𝜏1
𝜏2
𝜏3
𝜏4
𝜏5
𝜏1
𝜏2
𝜏3
𝜏4
𝜏5
𝜏1
𝜏2
𝜏3
𝜏4
𝜏5
𝜏1
𝜏2
𝜏3
𝜏4
𝜏5
Worker 1:
Worker 2:
Worker 3:
Worker 4:
𝜏1
𝜏2
𝜏3
𝜏4
𝜏5Worker 5:
System throughput is governed by the slowest worker: 50us (Worker 3)

20. 3.7 Process in Dualcore
Forward
Kinematics
Running
Algorithm
PD Control Jacobian
Current
Commands
Receive
Sensor Data
Main Controller
Think
(Process)
Act
(Transmit)
Sense
(Receive)
Main Controller
Dualcore CPU

21. 3.7 Process in Dual-core
𝑇𝑘𝑅 𝑘 𝑃𝑘 𝑇𝑘+1𝑅 𝑘+1 𝑃𝑘+1
Time
· · · · · ·
∆𝑇𝑅 ∆𝑇𝑃 ∆𝑇𝑇
∆𝑇
CPU
𝑇𝑘𝑅 𝑘
𝑃𝑘
𝑇𝑘+1𝑅 𝑘+1
𝑃𝑘+1
Time
· · · · · ·CPU 2
CPU 1
∆𝑇
𝑘 𝑡ℎ iteration 𝑘 + 1 𝑡ℎ iteration
Single CPU
Dual-core CPU

22. 3.7 Process in Dual-core
idle
idle
𝑇𝑘𝑅 𝑘
𝑃𝑘
Time
· · · · · ·CPU 2
CPU 1
∆𝑇
𝑘 𝑡ℎ iteration
𝑇𝑘+1𝑅 𝑘+1
𝑃𝑘+1
𝑘 + 1 𝑡ℎ iteration
idle
idle 𝑅 𝑘+2
𝑃𝑘+2
𝑇𝑘−1 𝑅 𝑘+3𝑇𝑘𝑅 𝑘
𝑃𝑘
𝑇𝑘+2𝑅 𝑘+2
𝑃𝑘+2
Time
· · · · · ·CPU 2
CPU 1
∆𝑇 2
𝑘 𝑡ℎ iteration
𝑇𝑘+1𝑅 𝑘+1
𝑃𝑘+1
𝑘 + 1 𝑡ℎ iteration
Make ∆𝑇𝑃𝑟𝑜𝑐𝑒𝑠𝑠 = ∆𝑇𝑅𝑒𝑐𝑒𝑖𝑣𝑒 + ∆𝑇𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑡
Removing the idle states

23. 3.8 Final Magic: SIMD
Scalar Operation
a=[1 3 5 7];
b=[2 4 6 8];
for i=1:4
c(i)=a(i)+b(i);
end
SIMD Operation
a=[1 3 5 7];
b=[2 4 6 8];
c=a+b;
a0 b0 c0
a1 b1 c1
a2 b2 c2
a3 b3 c3
+ =
+ =
+ =
+ =
a0 b0 c0
a1 b1 c1
a2 b2 c2
a3 b3 c3
+ =

24. 3.8 Final Magic: SIMD
Benchmark test results with many legs: 1. PD Control
50000
0
10000
20000
30000
40000
10000 200 400 600 800
Number of Legs
ExecutionTime(ns)
20
0
5
10
15
10000 200 400 600 800
Number of Legs
Scalar Operation
SIMD Operation
2500 times faster for 1000 legs

25. 4.
Design Principles for
Energy Efficient
Legged Locomotion
Design Principles for Highly Efficient Quadrupeds and Implementation on the MIT Cheetah
Sangok Seok, Albert Wang, Meng Yee (Michael) Chuah, David Otten, Jeffrey Lang and Sangbae Kim
2013 IEEE International Conference on Robotics and Automation (ICRA)
Design Principles for Energy Efficient Legged Locomotion and Implementation on the MIT Cheetah
Sangok Seok, Albert Wang, Meng Yee (Michael) Chuah, Dong Jin Hyun, Jongwoo Lee, David Otten, Jeffrey Lang, and Sangbae Kim
2014 IEEE/ASME Transactions on Mechatronics

26. 4.1 Energy Flow Diagram
Energy Source
(Battery)
Actuator
(EM Motor)
Positive
work
(Wposi)
Mechanical
Transmission
Ej
Negative
work
(Wneg)
Mechanical Energy
(Ek + Ep)
Ef
Ei
Principles ImplementationSystem Energy Flow
High Torque Density
Motor
Energy
Regeneration
Low Impedance
Transmission
(Back Drivability)
Low Inertia Leg
Large Gap Radius Motor
Efficient Driver Design
Single-stage Low Gear
Transmission
Dual Coaxial Motor
Differential Actuated
Spine
Composite Leg/
Biotensegrity
Joule Heating
Friction
Interaction

27. 4.2 Energy Regeneration
Deceleration Acceleration
Touch Down
Lift Off
m
Stance Phase Flight Phase
Ground

28. 4.3 Energy Efficiency for Animals and Robots
MIT Cheetah
(0.5)
ASIMO (2)
Bigdog (15)
Human
Running
Cheetah
LogMinimumcostofTransport,P/(WV)
EfficiencyHigher(logscale)

29. 5.
What’s Next?

30. 5.1 MIT Cheetah 2, Hermes