Mobile robots

Transcript

Mobile robots

Development of the ShAPE mobile robot
A.Tasora, Dipartimento di Ingegneria Industriale, Università di Parma, Italy
slide n. 1
Mobile robots
Development of the
ShAPE mobile robot
Ing. A.Tasora
Dipartimento di Ingegneria Industriale
Università di Parma, Italy
[email protected]
slide n. 2
Structure of this lecture
• Section A:
Introduction to AGV: mobile robots
• Section B:
Design of the ShAPE mobile robot
1
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Section A:
Introduction to AGV: mobile robots
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Autonomous guided vehicles
• Mobile robots: used for
– surveillance
– logistics
– entertainment, etc.
• Solutions are different in terms of
–
–
–
–
method of locomotion (wheels, legs, tracks, etc.)
payload & speed (performance)
navigation system
etc…
2
slide n. 5
Some ready-to-use AGV
•
Esatroll ‘Paquito’
– Max speed 1.3 m/s
– with laser scanner and bumpers
•
Proxaut ‘MT10’
– Max speed 1.3 m/s
– Max payload 1000 kg
– LGV navigation, with laser and gyroscope
slide n. 6
Some ready-to-use AGV
•
Skilled ‘MT10’
–
–
–
–
Max speed 1.5 m/s
Max payload 2500 kg
LGV navigation, with laser
Repeatability: 10 mm
3
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Locomotion systems
•
Propeller / jet / rocket.. (UAV, unmanned aerial vehicles)
– 6-DOF navigation
– GPS + gyroscopes + magnetic gyrocompass + vision awareness + laser
altimeter + accelerometers (and Kalman filter…)
•
Legs
– Difficult to control
– Useful for uneven
pavements
– Not useful for industrial
environments
•
Tracks / snakes / etc.
– Mostly for research – not in industry
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Locomotion systems
•
Three ‘Interroll’ omnidirectional wheels
– No need to turn wheels: direct
transmission with 3 motors
– All types of 3-DOF manouvers
on 2D plane
– Not suited for high speeds
– Not suited for high loads
– Possible improvements
(‘Mecanum’ wheels)
4
slide n. 9
Locomotion systems
•
3 or 4 fully steerable wheels
– All types of 3-DOF manouvers
on 2D plane
– Good performances but…
– Complex design (more
motors than DOFs)
slide n. 10
Locomotion systems
•
Two parallel wheels and one steerable wheel
–
–
–
–
–
Simplified design
Only two motors
Good speed & payload (ex. industrial environments)
Not all 3-DOF motions in 2D are possible! (non-holonomic constraints)
Two different approaches:
‘Differential wheels’
‘Motorized steering wheel’
m1
m2
m1
m2
5
slide n. 11
Locomotion systems
‘Motorized steering wheel’
m1
m2
•
Advantages:
– Front wheel never gets stuck
•
Disadvantages
– Two sizes for the motors
– One of the two motors works much more than the other
– The mechanism for steering requires vertical space
slide n. 12
Locomotion systems
m2
m1
•
Advantages:
–
–
–
–
•
Same size for motors, reducers and controllers
Both motors are used for accelerating lightweight design
Very simple to build
Small footprint
Disadvantages
– The front wheel has passive steering, it can ‘get stuck’..
6
slide n. 13
Navigation systems & sensors
•
How to get the absolute position (x, y, θ ) of the robot?
•
Odometric data (recordings of wheel
rotation) is not enough! It accumulates
errors – it must be integrated with other
more ‘absolute’ information..
YI
YR
XR
θ
G
•
Absolute position must be updated
in real-time, as fast as possible
•
No need for extreme precision (10 mm repeatability is good)
•
Solution? Different systems are used….
XI
slide n. 14
•
Robot on railways / on guides
– Easy solution, but not flexible…
– Requires expensive modifications to the building floor/roof
•
Wires in the floor & inductive sensor
– Easy solution, not 100% flexible…
– Requires expensive modifications to the building floor
•
Optical lanes painted on the floor
– Easy solution, not 100% flexible…
– Cheap modifications to the building floor, but painted lines on the
ground can be covered by dirt
7
slide n. 15
•
Gyroscopes
– Only rotation information
– Mechanical / Laser ‘Sagnac effect’ / Piezo (MEMS)
– Only piezo gyros are cheap, but easily accumulate drifting..
•
Magnetic gyrocompasses
–
–
–
–
Only rotation information
Extremely cheap (two IC fluxometers)
Measure the magnetic field of Earth absolute, but low precision
Affected by disturbs
slide n. 16
•
Satellite GPS
– Only x,y position
– Not precise enough (but cheap)
– Requires open air
•
MEMS gyroscopes + MEMS accelerometers ( + gyrocompass + …)
–
–
–
–
3 DOF rotation without drifting
Useful for attitude of UAV, drones, etc
Redundant sensors: exploit Kalman filters
Adding GPS for translation too: full 6 DOF
8
slide n. 17
Example: a quadcopter drone with autopilot (Ilmenau University , DE)
slide n. 18
•
Laser navigation (LGV)
– Both x,y position and rotation
– Very used for industrial AGV
– Rotates a laser and sees when
it hits some fixed reflective
markers in the building
– Problems with occluded
markers / bad illumination
– Not that cheap…
9
slide n. 19
•
Feedback with artificial vision
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•
1) One or more camera on the roof ‘see’ the AGV
2) Image analysis software can extract features from camera views
3) Position of AGV is obtained in view field, then trasformed to abs.space
No need to put the computer on the robot
Often used for small robots (soccer robot games, etc)
Robots must have recognizable symbols on their top (problems with bad
illumination, etc.)
Artificial vision awareness (SLAM approach)
– The camera is mounted on the robot the robot ‘looks’ at the
environment which it navigates, while an AI software with artificial vision
can understand the position respect to known objects (walls, windows).
– Very complex sw, low robustness not ready for industrial applications.
slide n. 20
Section B:
Design of the ShAPE
mobile robot
10
slide n. 21
Operating environment
•
•
•
•
The robot must carry small boxes filled with plastic materials
Small footprint is required (max 1m length)
No need to buy large commercial AGV
We developed a custom AGV, with simple navigation method based
on feedback from fixed videocameras and image analysis
slide n. 22
•
The carthesian robot which assists the AGV and the storage system
11
slide n. 23
•
The storage system: how the load/unload buffer works
slide n. 24
Locomotion system
m2
m1
•
We choose the ‘differential’ system because, among other
advantages, allowed us to keep the vertical size of the load plane
under the strict requirement (150 mm)
12
slide n. 25
Overall sizing
slide n. 26
Choosing motors and transmissions
Requirements:
•
•
•
Speed: 1 m/s
Ramps: 8%
Accelerations: as from various
benchmark for typical duty cycles..
Results:
•
•
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Reducers ratio: 1/20
Wheel diameter: 120 mm
Brushless motors LENZE Fluxxtorque 931E
(0.8 Nm nominal torque)
13
slide n. 27
•
Lenze brushless motors (24V)
slide n. 28
•
The worm reducer
– Low precision (some backlash) and low efficiency but…
– ..fits into budget constraints
– ..and takes small room in the robot frame
14
slide n. 29
Mechanical design
•
The aluminum truss
slide n. 30
Mechanical design
The box for drive controllers, electronic
devices and accumulators
15
slide n. 31
Mechanical design
Details
slide n. 32
Mechanical design
The wheel: it must touch the ground in a point (i.e. the smallest possible area)
Bearings must be resistant (1000N of radial force)
16
slide n. 33
Mechanical design
The pivoting wheel must be as stiff as possible, with toroidal surface, so that it does
not create unwanted frictional effects during changes of direction.
We tried different types of materials. Cast polyurethane is worse than hard
polyammide. Cylindrical tire is worse than beveled or toroidal surface.
slide n. 34
Electrical design
The 24V power circuit
17
slide n. 35
Electrical design
The accumulators: 4 x 27Ah standard lead batteries
Predicted continuous operating time without need to recharge: 2h.
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Control
•
The AGV is controlled by a remote computer using Wi-Fi ethernet
•
The remote computer is fixed to ground (it does not waste electric
power) while on the AGV there are only simple controllers for the
simplest tasks
•
The remote computer is also responsible of complex image analysis
from the fixed videocamera
18
slide n. 37
Control
•
• Hi-Res
Videocamera
•
firewire
•
Router
wireless
•
Bridge
wireless
•
Converter
Ethernet CAN
Remote
computer
•
MCU realtime controller
Drives of the
two motors
CAN bus
Ethernet
Wireless
IEEE 802.11g
Ethernet
slide n. 38
Control
Bridge wireless
•
Converter ethernet/CAN
Note!!! This CAN-over-WiFi scheme is enough for the prototype, but NOT for hard-real-time
environments (an embedded controller should take care of RT)
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slide n. 39
Control
The two drives for the control of the brushless motors
slide n. 40
Software
The software updates the state of the robot each 20ms
Acceleration / speed / rotation ramps for the two wheels are calculated
on-the-fly, so the speed setpoint is continuously passed to the two
controllers with CAN telegrams:
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slide n. 41
Software
The user
interface
Allows:
- jogging
- storing a
position list
- programming
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Software
•
Example of program running through a position list
21
slide n. 43
Repeatability
Test: good results even with open-loop feed-forward only
slide n. 44
Examples
22
slide n. 45
Conclusions
• The ShAPE mobile robot is a custom AGV with good
performance and low cost
• Global positioning comes from artificial vision
• CPU-intensive operations are performed on a computer
that is fixed to ground
• Information passed to the AGV using Wi-Fi devices.
23

Mobile robots

Transcript

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