ARTISAN - Stanford University Computer Science

1

Human-Friendly Robot Design

Torque Control

• manipulation

• cooperation

• safety, interactivity

• compliance, force control

• dynamic performance

: a basic capability

ARTISAN(1990-95)

ARTISAN(1990-95)

2

intelligence

for

mechanisms

Safety

Safety

Performance

Competing?

Requirements

Human-Friendly Robots Human-Friendly Robots

• Dependable & Safe• Soft Actuators• Light Structures• Impact-Reduction Skin• Low Reflected Inertia• Distributed Sensing• Good Performance

PumaConventional Geared Drive:

• Lighter structure

• Large reflected actuator inertia

Jmotor

Ngear

Jlink

Jmotor

Ngear

Jlink

(Jlink + N2Jmotor)

Effective Inertia

Heavy structure

Technology

Puma

Effective Joint Inertia

2( )rigid body i motor iA A diag N J

3

Safety Metric

Effective MassNormalized

PUMA560 (Payload 20N)

1.16

Safety Metric

Normalized Effective Mass

Human (Payload 60N)

0.04


1.16

Safety Metric


Human (Payload 62N)

0.04

DM2 (Payload 60N)

0.06


1.16

Safety Metric


Human (Payload 62N)

0.04

DM2 (Payload 60N)

0.06

2s (Payload 33N)

0.02

Inertia Property

1

1( )u Tu u

Effective Inertia/mass perceived in a direction u u

Acceleration Capacity

:E Torque to Acceleration Transmission

4

Acceleration CapacityOptimized Design

Initial Design Optimized Design

Why Are Robotic Arms Unsafe?

Robot Collision

Head Injury Criteria (HIC)

Torq

ue

Mag

nit

ud

e

Frequency

Actual Torque Requirements

Actuation Requirements

Torque Vs Frequency: Square Wave

+

Assumed Torque Requirements

Torq

ue

Mag

nit

ud

e

Frequency

ElasticCoupling Large Base

Actuator

Parallel Actuation

Small JointActuator

Distributed Macro Mini (DM2) Approach

Robot Characteristics

Equivalent Mass-Spring Model

Robot Collision

• Effective Inertia• Effective Stiffness• Impact Velocity

Effective Inertia at Contact

1 1 Tv vJ A J 1

1a T

v

Iu u

5

2coseK K 1 1 1

a hk k k

Effective Stiffness

with

Impact Velocity

Manipulator Safety Index (MSI) Manipulator Safety Index (MSI)

Variation with contact point – Interface Stiffness constant at 20KN/m

Manipulator Safety Index (MSI)

Variation with Configuration – Interface Stiffness constant at 20KN/m

“the high capacity of a large robot with the fast dynamics and safety of a small one”

DM2 - Human-Friendly Robot

6

To

rqu

e M

agn

itu

de

+

Joint actuator(high frequency)

Base actuator(low frequency)

Elastic Coupler

(Torsional Spring)Mini actuator

Brushless motor

Macro actuator

Brushed DC motor

DM2 New Testbed DM2 vs. PUMA 560: Effective Mass Comparison

PUMA 560 (link 2 and link 3)

HFR (conventional actuation)

HFR (DM2 actuation)

Maximum effective mass:

PUMA 560: 24.37 kg

HFR (Macro actuation): 12.71 kg

HFR (DM2 actuation): 2.81 kg

10

20

30

30

210

60

240

90

270

120

300

150

330

180 0

10x reduction in effective inertia

3x increase in position control bandwidth

10x decrease in trajectory tracking error

SafetyAND

Performance

DistributedMacro-MiniActuation

DM2

DM2 Performance

7

DM2 - Hybrid Actuation

artificial muscles with compact pressure regulators pneumatic artificial muscles


pneumatic artificial muscles








8


artificial muscles with compact pressure regulators

Human-Friendly Robot Design – DM2

2.S

: Stanford Human-Safe Robot 2s : Stanford Human-Safe Robot

muscle 300N @ 4bar

upper arm 34cm

lower arm 29cm

total mass 1.5kg

torque (7.5,5.0)Nm

mini (1.0,0.3)Nm

force@effector 14N

2.S

Macro……………0.5HzMacro/Tension 7.0HzMacro/Mini……. 35Hz

Ps

F2

F1

Load Cells

Pressure Regulator

Pressure Regulator

U2

U1

P1

P2

Tj,θ

0.4 0.6 0.8 1 1.2 1.4 1.60

0.5

1

1.5

2

2.5

3

3.5

4

Time [ sec ]

Posi

tion

[ de

g ]

Desired Pos it ion

M acro

DM 2

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Time [ sec ]

Tor

que

[ N

m ]

D esired T orque

M acro

D M 2

Stanford Human-Safe Robot

9

Virtual Wall (macro only/macro-mini)

1.52s : New Design 1.52s : New Design

Safety Comparison

Effective Mass: 1.2Kg

DM2


Human


PUMA560

Effective Mass: 25Kg

2s

: Stanford Human-Safe Robot 2s

10

: Stanford Human-Safe Robot 2s

Impact-reducingproximity andpressure sensingSkin using SDM

2 : Stanford Safety Robot

2 2.0 : New Design 2 Testbed

+

Pneumatic Muscle(low frequency)

Electrical Motor(high frequency)

2 Experimental ResultsMacro Macro + Mini

Position

Force

6Hz 26Hz

Safety Comparison

11

Safety Comparison 2 : Motion Range(sine wave)

2 : Contact Force Control

ARTISAN - Stanford University Computer Science

Documents