Team Design Process for a 6x6 All

Transcription

Experimental Validation
of Stable Obstacle Climbing
with a Four-Wheel Mobile Robot
OpenWHEEL
i3R
4W Stable
Climbing
[email protected]
[email protected]
[email protected]
Clermont-Ferrand, France
LaMI
UBP
IFMA
TIMS
Mechanical
Engineering
Research
Group
Blaise
Pascal
University
French
Institute for
Advanced
Mechanics
Research
Federation
Fauroux / Bouzgarrou / Chapelle
LaMI, Clermont-Ferrand, France
MTM2008 - 10th International Conference
on Mechanisms and Mechanical Transmissions
8-10 October 2008, Polytechnichal University of Timisoara, Romania
1
Introduction
More agile mobile robots needed in the future
4W Stable
Climbing
Spatial exploration
Mars exploration robot
A rover for sample analysis
www.nasa.gov/centers/jpl
Introduction
Agile robots
Locomotion
Challenging usual
applications
Exp. settings
Experiment
Conclusion
Wheeled ATVs are blocked on
ground discontinuities
Wheelchair blocked before an obstacle
2
Introduction
One big machine
✔
4W Stable
Climbing
Agriculture
A fleet of agile robots
✔
Rescue
Fleet of robots
to avoid soil
compaction
Introduction
Agile robots
Locomotion
Earthquake Mag. 7.4 Turkey (1999)
Scanning the streets and buildings
Exp. settings
Experiment
✔
Beach cleaning uses big machines or manual cleaning
Conclusion
Beach pollution
Towed filtering machine
Manual cleaning
3
Introduction
This work is about:
✔
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
Conclusion
✔
✔
✔
Wheeled robots
That climb step obstacles
With only four wheels
And stable behaviour
Within the OpenWHEEL framework
Wireless
connection
A3
Rear
S 32
Control
S 31
Wheel
W31
A2
I2
S 21
W21
Double
wishbone
W22
Innovative
suspension
S 11
W11
S 12
A1
Control
I1
W12
Camera
S22
Control
Suspension mechanism Saw
Swing arm
CAN Bus
W 32
n
Fro
t
Z
X
Y
Inter-axle mechanism Ia
Serial
Parallel
Innovative
mechanism mechanism mechanism
4
Agile mobile robots
Terrestrial locomotion system
✔
✔
4W Stable
Climbing
✔
- unilateral / bilateral
- slipping / sticking
- can change in nature and number
Terrestrial vehicles & robots
✔
Introduction
Poly-articulated mechanical system
Interact with environment
Contacts with the ground
✔
✔
Wheeled vehicles prevail (energetic efficiency ?)
Blocked on slope discontinuities of the ground
Legs / Tracks regain interest for climbing
Agile robots
Interface with the ground
Locomotion
✔
Crawler
+ multiples contacts, can cross obstacles & rough terrain
- require high energy, moderate speed, complex control
Experiment
✔
Leg
+ can cross obstacles and go fast on rough terrain
- contact discontinuity, energy cost, stability control
Conclusion
✔
Wheel
+ fast on smooth surface, energy efficient
- cannot climb obstacles or run on rough terrain
✔
Track
+ permanent stability, high traction
- high friction energy loss, particularly during steering
Exp. settings
5
Mobile robots based on legs
✔
✔
✔
Bi / Quadri / Hexa / Octo
Natural gait / self-teaching
Legs with feet = wheels
4W Stable
Climbing
Yanboo III (13kg,0.7m high)
Biped with suction/rolling effectors
Legs are manipulators
www-robot.mes.titech.ac.jp
Introduction
Agile robots
●
Leg
●
Wheel
●
Hybrid
Locomotion
Exp. settings
Experiment
Conclusion
Big Dog (75kg, 1m long, 6km/h,
35° slopes, 150kg payload)
www.bostondynamics.com
Roller-Walker (24kg, 0.5m long)
Convertible wheels / Dual locomotion
mode: walking / roller-skating
6
Wheeled robots
✔
✔
Wheel: energy efficient even when steering
Only exception : skid steering
4W Stable
Climbing
Introduction
Agile robots
●
Leg
●
Wheel
●
Hybrid
Locomotion
Exp. settings
Experiment
Conclusion
Pioneer P3-AT
Skid steering simple robot
www.mobilerobots.com
Nomad
Dual Ackermann steering strategy
www.frc.ri.cmu.edu/projects/lorax
7
Adaptative Wheeled Robots
✔
✔
Minimally actuated frame, energy efficiency
Simple control
4W Stable
Climbing
Introduction
Agile robots
●
Leg
●
Wheel
●
Hybrid
Locomotion
Micro5
Climbing abilities via 5 wheels
www.mit.edu/~ykuroda
Rocky 7
Adaptative rocker-bogie structure
www-robotics.jpl.nasa.gov
Exp. settings
Experiment
Conclusion
8
Adaptative Wheeled Robots
Crab I
Adaptative parallel bogies
Obstacle climbing abilities
www.asl.ethz.ch
4W Stable
Climbing
Introduction
Agile robots
●
Leg
●
Wheel
●
Hybrid
Shrimp
6 wheels on 2 // bogies
and 1 front linkage
www.asl.ethz.ch
Locomotion
Exp. settings
Experiment
Conclusion
9
Hybrid multi-mode robots
✔
✔
4W Stable
Climbing
Highly actuated frame
Orientable tracks for special modes of
displacement
Introduction
Agile robots
●
Leg
●
Wheel
●
Hybrid
Locomotion
Exp. settings
Experiment
Azimut
4 orientable tracks
www.gel.usherbrooke.ca/laborius
Conclusion
Helios VII
2 articulated tracks + 1 manipulating
arm with hybrid
grip/wheel end effector
10
Hybrid multi-mode robots
✔
✔
4W Stable
Climbing
Introduction
Agile robots
●
Leg
●
Wheel
●
Hybrid
Highly actuated frame
Displacement modes: peristaltic crossing,
obstacle climbing
RobuROC 6 (150 kg, 1.5m long)
3 tiltable axles with passive warping
Able to turn on itself
Can climb obstacles
www.robosoft.fr
Locomotion
Exp. settings
Hylos (0.5m long)
4 wheels on 3DOF legs
www.robot.jussieu.fr
Lama
Peristaltic crossing
of sandy areas
www.laas.fr
Experiment
Conclusion
11
Chosen locomotion modes
for OpenWHEEL
Chosen architecture
4W Stable
Climbing
Introduction
Agile robots
Locomotion
✔
✔
✔
✔
OpenWHEEL
●
OW i3R
✔
●
Stability
✔
Experiment
Conclusion
Rolling
Climbing step obstacles
Multi-modes
Only four wheels
✔
Climbing
Exp. settings
Hybrid robot
Two locomotion modes (at least)
●
●
Wheels (efficiency)
On legs (climbing ability)
No existing robot that climb with only four wheels
A challenge for stability during climbing
Easier to transfer on real vehicles
Few actuators
✔
✔
Actuated wheels
Few actuators in legs/frame for better
simplicity / stiffness / consumption / price
12
OpenWHEEL i3R
i3R = 3R inter-axle mechanism
✔
✔
4W Stable
Climbing
Introduction
2 passive R joints in the middle of the axles
1 actuated R joint for central warping
Kinematic structure with double symmetry
OpenWHEEL i3R
A big central actuator for warping
Passive joint
Axle steering without robot motion
Agile robots
Locomotion
●
OpenWHEEL
●
OW i3R
●
Stability
●
Climbing
ar
e
R
Exp. settings
Experiment
Conclusion
W21
W22
nt
o
r
F
W11
W12
Four actuated wheels
More space for payload
13
Stability criterion on 3 wheels
2D modelling when lifting one wheel
Introduction
Agile robots
Wheel W12 (front-left)
Wheel W21 (rear-right)
1)
2)
3)
Front axle steering
4W Stable
Climbing
Wheel W11 (front-right)
W12
4)
W11
G
G
G
●
OW i3R
●
Stability
●
Climbing
5)
Rear axle steering
OpenWHEEL
W22
G
W21
Locomotion
●
Wheel W22 (rear-left)
W11
G
6)
W12
7)
G
8)
G
G
W21
W22
Exp. settings
Experiment
Conclusion
Stable
Unstable
Stable
Unstable
Stability if the lifted wheel is inside the turn
14
Stability during climbing
3D modelling
Stability margin on 3 wheels when climbing = HG'
4W Stable
Climbing
Introduction
W12
Exploring wheel
Agile robots
Obstacle
G1
Locomotion
●
R0
W11
OpenWHEEL
●
OW i3R
●
Stability
●
Climbing
Exp. settings
R1
G
W22
R2
P21
P12
H
G'
G2
W21
Experiment
Conclusion
P22
15
Climbing process
Climbing sequence in 7 phases / 19 stages
1
4W Stable
Climbing
A - Prepairing
W22
Low
Introduction
2
W12
B - W 11 climbing
3
4
5
C - W 12 climbing
7
8
9
E - W 21 climbing
12
13
14
17
18
19
High
W21
W11
6
Agile robots
Locomotion
●
OpenWHEEL
●
OW i3R
●
Stability
●
Climbing
Exp. settings
10
D – Going forward
15
F - W 22 climbing
11
16
G - Conclusion
Experiment
Conclusion
16
Climbing process
Strong simplifying hypotheses
✔
4W Stable
Climbing
Introduction
✔
✔
✔
✔
Agile robots
Negligible mass of the inter-axle mechanism
Non-deformable bodies (i.e. infinite part stiffness)
Small warping rotation-angles to avoid representation of
complex 3D poses
Punctual ground-wheel contact with toric wheels
Perfect rolling without slipping assuming that normal
forces are sufficient to ensure enough traction
Locomotion
●
OpenWHEEL
●
OW i3R
●
Stability
●
Climbing
Incremental validation
✔
✔
✔
Multi-body Adams model [IROS 06]
Reduced model [MTM 2008]
Full scale model [in process...]
Exp. settings
Experiment
Conclusion
17
Wheel sub-assembly
Four identical wheel sub-assemblies
✔
4W Stable
Climbing
✔
✔
✔
One 9V actuator : 200 rpm, 3.52 N.cm on top of the wheel
Transmission ratio 1/15
Rubber air-tire with good friction (Diam 49.6 mm)
Overconstrained structure - mass 149 g
Introduction
2
Agile robots
Locomotion
Z40
Z8
3
C
Exp. settings
●
Wheel
●
Inter-axle
●
Whole robot
●
E
0
Z8
Software
Experiment
Z24
1
Conclusion
18
Inter-axle mechanism
High torque warping mechanism
✔
4W Stable
Climbing
Introduction
✔
✔
✔
✔
The same 9V actuator as for the wheels
Transmission ratio 1/560
Double worm gear redundant overconstrained transmission
Minimized backlash
Improved tooth strength
Agile robots
Z16
Locomotion
Exp. settings
●
Wheel
●
Inter-axle
●
Whole robot
●
F1
Z16
Z8
E
F2
Z8
Software
Z56
Experiment
Z40
Conclusion
19
Whole reduced model of the robot
Whole assembly = 2 axles + 1 inter-axle mechanism
4W Stable
Climbing
✔
Total weight
1430 g
✔
Center of
mass quasicentered
Introduction

G1 G=0.497
G1 G2
Agile robots
Locomotion
✔
●
Wheel
●
Inter-axle
●
●
Whole robot
Software
Experiment
✔
Translation
speed 55mm/s
✔
Warping speed
45° in 21s
(with oil)
170 mm
Exp. settings
G1
Carries its
power (12 AA
batteries)
G
G2
W12
17
5 m
m
W22
m
0 9
1
m
Conclusion
20
Software architecture
Embedded program in each control unit
NQC language, BricxCC developing environment
4W Stable
Climbing
✔
Introduction
✔
✔
✔
Control unit 1 for axle 1 (Master)
Control unit 2 for axle 2 and warping joint R0 (Slave)
Exchanges between units via infrared port
Protocol by message sending and detection loop
Agile robots
Locomotion
Exp. settings
●
Wheel
●
Inter-axle
●
Whole robot
●
Master program for A1
Slave program for A2+ R0
// Stage 2 : rev W22 / fwd W21
Bip();
SendMessage (2);
ClearMessage();
until (Message() == 2);
// Stage 2 : rev W22 / fwd W21
if (Message() == 2)
{
OnRev (W22);
OnFwd (W21);
Wait(150);
Off (W22+W21);
SendMessage(2);
}
Software
Experiment
Conclusion
21
Experimental climbing
Purpose: validating the climbing strategy
✔
4W Stable
Climbing
✔
✔
Obstacle: 55 mm high
Higher than a wheel
Actuators at full speed with open loop control
Useful to determine the most suitable sensors
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
Difficulties
✔
✔
Initial tests with stabilized power – Final test with batteries
Difficult to debug: the final pose depends on the full process
22
Phase A – Stage 01
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
23
Phase B – Stage 02
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
24
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Optional: going against the
obstacle and actuating the wheel
for bonus tangential force
Improvement
Conclusion
25
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
26
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Optional: the exploring wheel can
land faster if it was lifted just at the
level of the obstacle
Improvement
Conclusion
27
Phase C – Stage 06
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
With pitch angle and contact on four wheels, steering Axle A1 is coupled with warping the frame
Improvement
Conclusion
28
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
W11 serves as a pivot for Axle A1
Slipping risk on W11
Improvement
Solution: unsteer slightly Axle A2
Slightly lifts W12
Conclusion
Increase normal force on W11
●
29
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
30
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
31
Phase D – Stage 10
4W
Stable
W and
W with same speed set point
Normal forces differ
Climbing
11
12
Induced steering on axle A1
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
Improvement
Solution: closed-loop control
- to equilibrate normal forces
Conclusion
- to keep a constant steering angle
●
32
Phase E – Stage 11
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
33
4W Stable
Climbing
Introduction
Agile robots
Solution: additional
149 g counterweight
Locomotion
Exp. settings
Experiment
Risk ●ofClimbing
instability
during W21 climbing
● Adjustments
●
●
Control
Improvement
Conclusion
34
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
35
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
Climbing
Optional: the exploring wheel can
land faster if it was lifted just at the
● Adjustments
level of the obstacle
●
●
●
Control
Improvement
Conclusion
36
Phase F – Stage 15
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
●
●
●
Climbing
Optional: going against the
Adjustments
obstacle and actuating the wheel
for bonus tangential force
Control
Improvement
Conclusion
37
4W Stable
Climbing
Introduction
Riskrobots
of instability
Agile
during W22 climbing
Locomotion
Solution: additional
149 g counterweight
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
38
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
39
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
Conclusion
40
Phase G – Stage 19
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
●
Control
Risk of lateral drift
with respect to phase 1
Improvement
Conclusion
41
Design adjustments
Axle A1 climbs more easily than Axle A2
4W Stable
Climbing
Introduction
Need for a counterweight
✔
The counterweight breaks longitudinal symmetry
✔
Possible explanation: if the centre of mass G is too high, its
projection on the ground G' moves relatively to contact
points Pi and stability criterion is no more respected
Agile robots
Locomotion
G2
G
G1
Exp. settings
G
G2
Experiment
●
Climbing
●
Adjustments
●
Control
●
Improvement
G1
P1
P2
✔
G'
P1
P2
G'
The 149 g counterweight brings G forward of 16 mm

G1 G=m2 /m1m2 
G 1 G2=0.408
G1 G2
Conclusion
42
Control
Control laws for the 4 wheels and central actuator
✔
✔
4W Stable
Climbing
Introduction
Phases B-D-E-F are similar in length
Warping phases take 80% of time. Warping angle < 26°
700
Phase E
Angles of rotation of the actuators of OW i3R
600
Angle
Angle
Angle
Angle
Angle
500
Phase F
W12 (°)
W11 (°)
W22 (°)
W21 (°)
R0 (°)
Agile robots
400
Phase B
Locomotion
Phase C
300
Exp. settings
200
Experiment
100
●
Climbing
●
Adjustments
●
Control
●
Improvement
0
-100
2 3
45
6
7
8
9
10 11
12
13 14
15
16
17 18
19
-200
0
Conclusion
10
20
30
40
50
60
70
80
90
89 s
43
Control improvement
The good metrics for measuring climbing ability
4W Stable
Climbing
Introduction
Agile robots
Locomotion
✔
✔
✔
Better control to improve climbing
Adding sensors for precise monitoring
✔
✔
Exp. settings
Experiment
●
Climbing
●
Adjustments
●
Control
●
Not the wheel diameter
Comparison Obstacle height / Altitude of the centre of mass
OpenWHEEL i3R can climb obstacles as high as 67% ZG
✔
Angular coders on actuators (wheels + warping central joint)
Coders on passive joints (axle steering)
Ultra-sound sensor to detect obstacle / measure height
Rolling without slipping
✔
✔
Measuring normal force
Pitch → Two-axes force gauges in the rim of the wheels
Improvement
Conclusion
44
Conclusion
Results
4W Stable
Climbing
Introduction
✔
A new principle for stable obstacle climbing
✔
Usable with only 4 wheels for simplicity
✔
Only one supplemental central actuator
✔
A climbing process in 19 stages
✔
Validated on a reduced model of OpenWHEEL i3R
✔
Climbs obstacles as high as 66% of ZCentre of mass
Agile robots
Locomotion
Exp. settings
Experiment
Conclusion
In the future
✔
Geometrical model for coupled actuation of steering / warping
✔
Obstacle detection and control adaptation
✔
Normal force / slipping regulation
✔
Optimizing kinematics & structure
✔
Optimizing climbing strategy: how
much can we climb with 4 wheels ?
45
02
03
4W Stable
Climbing
04
Introduction
Agile robots
Locomotion
05
Next
step
?
Exp. settings
Experiment
Conclusion
06
A stable climbing process
Multibody validation (Adams)
Experimental validation on
actuated reduced model
46
Conclusion
4W Stable
Climbing
Introduction
Agile robots
Locomotion
Exp. settings
Experiment
Conclusion
Full scale demonstrator
140 kg, 1.4m long
47

Team Design Process for a 6x6 All

Transcription

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