58 Crawling, walking or rolling for obstacle-crossing ? Bio-inspiration for the OpenWHEEL i3R agile mobile robot
[email protected]
[email protected]
Clermont University – French Institute for Advanced Mechanics (IFMA) LaMI – B.P. 10448 – 63000 CLERMONT-FERRAND, France
Clermont University – Blaise Pascal University (UBP) LIMOS – B.P. 10448 – 63000 CLERMONT-FERRAND, France
Paradigm for stable climbing
OpenWHEEL i3R OpenWHEEL
- Crawling / Walking is used by most terrestrial animals : efficient in natural environment with irregular and unstructured ground but slow, difficult to control, and requires a lot of energy. - Wheels are used on most human vehicles : energy-efficient and fast but only on smooth and hard terrain. - Hybrid locomotion combines wheels and active legs or frame
Parallel Mechanism
Innovative Mechanism
OpenWHEEL i3R is an agile mobile robot with low actuation (only one central active joint, passive steering induced by wheel actuation) and multiple modes of locomotion for rolling on smooth surfaces or crossing obstacles
Inter-Axle Mechanism
WorkPartner (230 kg, 1.4m long, 7km/h) 4 wheels on legs (3 DOF per leg) automation.tkk.fi [Halme 2003]
I
Wireless connection
Data Bus
A1 ar Re Control Nomad Dual Ackermann steering strategy www.frc.ri.cmu.edu/projects/lorax [Rollins 1998, Apostopoulos 2001]
Roller-Walker (24kg, 0.5m long) Convertible wheels / actuators only on legs Dual locomotion mode: walking / roller-skating www-robot.mes.titech.ac.jp [Hirose 1996]
Serial Mechanism
S32
S22
A2 Control
I1
A3 Control
I2
S21
S31
Fro
nt
S11
Front frame (F1) Exploring wheel (W12) yW12
S11
Actuated Wheel Lama Peristaltic crossing of sandy areas www.laas.fr [Lacroix 2002]
- The present work aims at keeping the interesting obstacle crossing capacities of hybrid locomotion but replaces the multiple legs by a single deformable frame, that allows to decrease the number of actuators
Suspension Mechanism
Double Wishbone
1)
2)
3)
G
G
W 11
12V 48Ah traction battery
W22
zF2
yF2
24V actuator (330W)
8)
G
G W 21
Unstable
W 22
Stable
Unstable
T1 zA1 xA1
Front steering joint R1 Exploring front axle (A1)
OA1
0 zF1 xF1= xF2
G1
A11
B22
T2
G
W11
zA2 yA2
O11 hS
xA2 P11
H G'
A21
G2
Step Obstacle B21 O21
Reconfigured rear axle (A2)
Electromagnetic clutch
Climbing process
W21 P21 z0 y0
Curtis programmable DC controller
Dual-stage 10.9x chain transmission
rW
x0 O0
- Stability is evaluated by a simplified 2D model in top view (figure below, left column).
Wheel center motion
Wheel landing
- A 3D multibody model (Adams) confirms feasibility (figure below, rightcolumn) [Fauroux 2006]
Support polygon For a very stable configuration
ATV tire
(Four contact points)
For a stable configuration
(Three contact points)
W22
Phase A Preparing
W12
Vi
- 1.85m long, 1.38m wide, 0.98m high, 200kg - 24V DC actuators 330W with peak torque of 100Nm + external encoder + Two or four 12V 48Ah traction batteries - Central clutch → no overconstraint when rolling → no suspension required - Fast 45° central warping : only one second (15x faster than V1) - The same high level NXT controller as V2 generates 8kHz PWM Pulse Width Modulated motor signals - Used as an average tension to control low level Curtis DC controllers (24V, 70A)
Phase B W 11 climbing
2
OpenWHEEL i3R V2
3
Rotation sensor
9V 8 Ah battery
4
Motor multiplexer
5
Phase C W 12 climbing
Wifi remote
6
Control unit ARM 48 MHz 256 kB RAM
9V actuator (5W)
CAD model
Overconstrained zero clearance twin transmission Contact sensor
- Small scale (50cm) with closed loop control with access to PID parameters - Powerful 9V actuators (5W) and many sensors : contact, steering angle, distance (US), 3D accelerometer to measure tilting - When not horizontal, steering reconfiguration generates induced axle warping - Solution: unwarp the central joint / declutch the central joint
06
06
Without warping correction
With warping correction
7
- The whole robot V3 - Detail of the warping system : - reduction ratio 10.9 - max torque > 1000Nm - electric clutch
8
9
Steering-warping Coupling equation [Fauroux 2010]
sin 0 =−tantan 2
Phase D Going forward
Front frame (F1) is supposed fixed to the ground and submitted to a roll angle α and a pitch angle β
10
Phase E W 21 climbing
11
OpenWHEEL i3R V1
Bio-inspiration from balancing of walking natural creatures
12
OpenWHEEL i3R V1, a reduced model built with the Mindstorms RCX robotics kit - 1.5kg autonomous robot - The first to validate the autonomous climbing process - Open loop (no coders in the motors) - 9V DC actuators (1.1W) - Two controllers synchronized by IR message exchange - Best obstacle height : 55 mm, 67% of the height of the centre of mass
- Longitudinal balancing to increase stability: walking uphill induces for bipeds an increasingly flexed posture of hip, knee and ankle at initial foot contact as well as a progressive forward tilt of pelvis and trunk [Leroux 2002] - Solution : mounting batteries or payload on a longitudinal slider
[Muybridge 1883]
G1 170 mm
- OpenWHEEL i3R: a hybrid mobile robot with deformable frame - Can climb obstacles as high as 2/3 of the altitude of its centre of mass with only 4 wheels - Only 1 supplemental actuator → minimal actuation, good stiffness - 3 small and full scale implementations / 1 control architecture - Problems & solutions : front-rear non-symmetry, steering-warping coupling
13
G G2
W12 17 5 m
m
0 19
W22
m m
14
Front-rear non symmetry [Fauroux 2008]
Phase F W 22 climbing
- Axle A1 climbs easily whereas axle A2 has difficulties - Solved by adding a counter-weight CW of 150 g - Non-symmetry was not predicted because of 2D approximation - On flat ground, the 2D model is exact - With some pitch: - In 2D, stability margin P 2 G ' =b cos /2
- Lateral balancing during obstacle crossing: centre of mass of bipeds is moved laterally by combined rolling of hip and ankle [Hof 2007] - For OpenWHEEL, lateral balancing comes from steering reconfiguration (stages 3, 7, 12 and 17) - Complementary solution : lateral sliding of payload
15
P 2 G ' =b cos /2−hl hs /b
- In 3D
16
- Stability is favoured at stages 3 and 7 and penalized at stages 12 and 16 - Adding CW equilibrates the climbing capacities of front and rear axles
- The current obstacle-crossing process of OpenWHEEL i3R is very close quadruped locomotion (example of the cat) a)
2D model: On flat ground
b)
d)
2D model: On a step
3D model: stability margin nullifies
b G hl
- Improving volume for payload → Replacing the inter-axle mechanism by an exoskeleton, such as for arthropods
O0
rW
G' x0
P2
P1
P1
z0 x0 P2
O0
- Towards new robots & vehicles for agile all-terrain mobility & clearance performance
c)
3D model with counterweight CW: stability is back
hs
G'
18
3D model: On a step
e)
f)
G'
Phase G Conclusion
G'
G
CW
hl z0
The authors wish to thank the following students from IFMA and UBP for their contribution to this work : Guillaume MALVAL, Emilie PORTALES, Morgann FORLOROU, Sylvain MARCO, Yohann KOBERLE, Damien ROUX, Laurent GENEVAY, Michel TOU, Fabien BIANCHINI, Romain CARTAILLER, Farhat HZAG, Sylvain METAIS, Christophe NOELLAT.
O0
P1
rW x0
17
G'
G
z0
Example: Stage 12
2D model: supposed stable
P2
G'
19
W21
W11
High
Low
1
Sensor multiplexer
- The obstacle-crossing mode was created by interpolating between several stable configurations where the robot lays either on three or four contact points. - The complete process has 19 stages divided into 7 phases A-G. Phases B-C and E-F concern the front and rear wheels respectively and have a similar structure: - Steering the other axle for stability - Lifting the exploring wheel above the obstacle - Bringing the exploring wheel forward - Landing the exploring on the obstacle
Wheel lifting
05
G
B11
OA2
P22
G
OF1=OF2
A22 O22
W 22
7)
W 12
Rear steering joint R2
Battery and payload front cradle
G
6)
G
yA1
Rear frame (F2)
OpenWHEEL i3R V3
4)
W 21
xW12 A 12
O12
Central warping joint R0
Wheel W 22 (rear-left)
W 11
B12
Innovative Suspension
W 12
Stable
W12
Swing arm
Wheel W 21 (rear-right)
zW12
Wheel (W12) joint R12
S
Wheel W 12 (front-left)
5)
The rover can climb on obstacles with only 4 wheels: 3 wheels for stable support of the robot (points P11, P21, P22) and 1 exploring wheel to crawl over the obstacle (wheel W12 on figure below)
Vision
Wheel W 11 (front-right)
Front axle steering
A family of rovers developed at LaMI / IFMA with articulated frame and / or innovative suspensions
Static stability on 3 wheels - Configurations 2) 4) 6) 8) are unstable - The stable configurations 1) 3) 5) 7) occur when the exploring wheel is located on the inside of the turn
Origin of the name i3R: - i for the inter-axle central mechanism - 3R for the number of revolute joints used in this mechanism - two passive steering rotations for front and rear axles - one central active warping joint
Rear axle steering
Wheeled / Legged / Hybrid Locomotion on unstructured terrain
o de
2
o de i V
1
