Vítor M. F. Santos 1 Filipe M. T. Silva 2
-
Upload
silas-castro -
Category
Documents
-
view
30 -
download
1
description
Transcript of Vítor M. F. Santos 1 Filipe M. T. Silva 2
Centre for Mechanical Technology and Automation
Institute of Electronics Engineering and Telematics
TEMA
IEETA http://www.mec.ua.pt/robotics
Engineering Solutions to Build an Inexpensive Humanoid Robot Based on a Distributed Control Architecture
Vítor M. F. Santos1
Filipe M. T. Silva2
1 Department of Mechanical Engineering2 Department of Electronics and Telecommunications
University of Aveiro, PORTUGALUniversity of Aveiro, PORTUGAL
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Overview Introduction Initial considerationsMechanical conceptionActuators, power and batteriesServomotor issuesSensorial issues and force sensorsThe control architectureSome preliminary resultsConclusions and open issues
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Project framework Motivation
Develop a humanoid platform for research on control, navigation and perception.
Offer opportunities for under & pos-graduate students to apply engineering methods and techniques
The utopia of Man to develop an artificial being with some of its own capabilities…
Why not a commercial platform? Versatile platforms imply prohibitive costs! Reduces the involvement at lowest levels of machine
design Current status
So far, it is only a development engineering approach The platform prototype already performs some motion Early studies on control just began
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
To build or to buy? Several commercial platforms already exist:
Only a few offer great versatility, DOFs, possibilities of control, …
Good platforms (e.g., Fujitsu) have high costs (tens of thousands of Euros); others are not even for sale
Commercial platforms favour mainly high level software development
Developing a platform from scratch allows using hardware more oriented to the desired approach: Distributed control, special sensors, alternative central units …
Developing a platform from scratch takes longer, but hopefully can be done at lower costs…
Sony QRIO Fujitsu Sumo Bot
ZMP Nuvo
Kawada HRP1S
Honda Asimo
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Initial Considerations Main Objectives
Build a low-cost humanoid robot using off-the-shelf technologies, but still aiming at a fully autonomous platform
Have a working prototype capable of participating in the RoboCup humanoid league (Germany2006)
Design Concerns Consider a distributed control architecture due to
the expected complexity of the final system Assume modularity at several levels to ease
development and scalability Provide rich sensorial capabilities
Initial design Initial design
considerationsconsiderations::− Robot dimensionsRobot dimensions− Mobility skillsMobility skills− Level of autonomyLevel of autonomy
Initial design Initial design
considerationsconsiderations::− Robot dimensionsRobot dimensions− Mobility skillsMobility skills− Level of autonomyLevel of autonomy
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
The needed DOFs 6 DOFs per leg
Universal joint at the foot (2 DOFs) Simple joint on the knee (1 DOF) Spherical joint on the hip (3 DOFs)
• Total DOFs for the Legs = 2 x 6 = 12
Trunk with 2 DOFs To envisage better balance control
3 DOFs per arm without hand and wrists Universal joint on the shoulder (2 DOFs) Simple joint on the elbow (1 DOF)
• Total DOFs for the arms = 2 x 3 =6
Neck/head accounts for 2 DOFs To support a camera for vision perception
Total proposed: 22 DOFs
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Kinematics simulations Four Denavit-Hartenberg open
kinematics chains: One leg on the floor up to the
opposite foot not on the ground Starting on the hip, a 2nd chain
goes up to the neck. A 3rd and 4th chain for left and
right arms. Allows the analysis of:
Static torques Path of CoM and its projection on
the ground Opens the way to simulate:
Dynamics in higher speeds ZMP paths
Inputs for the model in Matlab: Links’ DH parameters Links’ masses Links’ centers of mass Path planning at joint level
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Mechanical conception
Foot
Ankle
Lower leg
Upper leg
Lower hip
Upper hip
Hip
Trunk joints
Trunk
Neck
Head base
Shoulder
Arm
Forearm
Final platfrom
3D model with 600+ components
and 22 DOFs
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Summary of mechanical properties Complete humanoid model
22 degrees of freedom Weight - 5 kg Height - 60 cm Max width - 25 cm Foot print - 20 8 (cm2)
Materials used for the body and accessory parts Aluminium (2.7 g/cm3) Bronze (8.9 g/cm3) Steel (7.8 g/cm3) Nylon (1.4 g/cm3)
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Actuators
Static (and some simplified dynamic) simulations were carried out to estimate motor torques in a simulated step
Best low cost actuators in the market are Futaba RF servos or similar (HITEC,…).
Available models best suited for our application are:
Application Model Mass (g) Torque (Nm)
Arms & small torque joints HS85BB ~20 0.35
Legs & high torque joints HS805BB 119 2.26
Additional mechanical issues for motors Use gear ratios up to 1:2.5 to rise torques Use tooth belt systems for easier tuning Use ball bearings and copper sleeves to
reduce friction
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Power requirements and batteries Motors
Max current: 1.2 – 1.5 A per motor (big size model)
Electronics and control Estimated to less than 200 mA per
board with a total of ca. 1.5 A. Voltage Levels
5 V for logic; 6.5 V for motors Two ion-lithium batteries were
installed (from Maxx Prod.) 7.2 V/9600 mAh per pack Maximal sustained current of 19A Each pack weights circa 176g Confined to a box of 373765 (mm3)
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Servomotor velocity “control”
Servomotors have an internal controller based on position User cannot directly control
velocity! Either replace motor own
control electronics or do some software tricks
Example: Two similar motors with different velocities Dynamic PWM generation Stepped target points Without load, open-loop and
feedback based actuation give similar results…
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
First results with one leg in motion Simple open loop actuation of the leg joints PWMs generated by dedicated boards (shown further on)
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Envisaged sensorial capabilities
Accelerometers for Accelerometers for accelerations and inclinationsaccelerations and inclinations
Gyroscopes for angular velocity Gyroscopes for angular velocity
Potentiometer for Potentiometer for position feedbackposition feedback
(HITEC Motor)(HITEC Motor)
GYROSTAR ENJ03JA GYROSTAR ENJ03JA from MURATA from MURATA
ADXL202E fromADXL202E fromANALOG DEVICE ANALOG DEVICE
Vision unit (on Vision unit (on the head)the head)
Motor electric currentMotor electric current
Serial power Serial power resistorresistor
Sensitive feet Sensitive feet
Strain gauges on a Strain gauges on a slightly compliant slightly compliant materialmaterial
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
The sensitive foot A device was custom-made using strain gauges
properly calibrated and electrically conditioned Four strain gauges arranged near the four corners of the foot
Strain Gauge
Flexible beam
Foot base
Adjustable screw
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Force sensors and motor connection
Foot sensor
PIC local board +Electric conditioning
Servomotor
Servomotor reacts to differences on sensors located on the edges of the foot
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Control system architecture
Distributed control system A network of controllers connected
by a CAN bus A master/multi-slave arrangement Each slave controller is made of a
PIC device with I/O interfacing.
Asynchronous communications Between master and slaves: CAN
bus at 1 Mbit/s Between master and high level
controller (currently serial RS232 at 38400 baud)
Main ControlMain Control
RS23RS2322MasteMaste
rr
CAN CAN BUSBUS
1
23 1
2
3
1
2
31
2 1
2
3
1
2
3
1
2
3
1
2
SlaveSlavess
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Functions of the control level units Main control unit
Global motion directives; high level planning. Vision processing Interface with possible remote hosts
Master CAN controller Receives orders to dispatch to the slaves Queries continuously the slaves and keeps the
sensorial status of the robot• Currently does it at ca. 10 kHz
Slave CAN controllers Generate PWM for up to 3 motors Interface local sensors Can have local control algorithms
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
The set of local controllers 7 slaves controllers for joints and sensors 1 master controller
Interfaces slave controllers by CAN Interfaces upstream system by RS232
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Local control boards All master and slave
boards have a common base upon which a piggy-back unit can add I/O (sensors, additional communications, etc.)
Power resistor (0.47)
16:1 multiplexer
CAN connector
Piggy-back socket
PIC Cristal oscillator
CAN driver
PIC
Unit CAN Address
PWM plugs
Servo fuse
Fuse status LED
Piggy-back board 2
Piggy-back board 1
Connector to sensor
CAN bus Power plug
Power regulator Reset button
RS232 plug
Connector to sensor
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Examples of piggy-back boards Accelerometers
Dual accelerometer
Dual amplifier
25 mm Strain gauges
conditioning Serial COM for master
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
First humanoid motion The robot is able to stand, lean on sides, for/backward Primitive locomotion motions have been achieved
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Low cost... How Low? Servomotors
Big size: ~50 € x 14 -> 700 € Smaller size: ~30 € x 8 -> 240 €
Miscellaneous electronic components Total -> ~300 €
Aluminium gears and belts Total -> ~300 €
Batteries ~80 € x 4 -> ~320€
Sensors (except camera) Negligible (<100€)
Raw materials (steel, aluminium) Negligible (<100€)
Total ~ €2000 Excluding manufacturing and
development costs (software, etc.) Still missing:
Vision unit, central control unit (PC104+), lots of software...
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
On-going and open issues Next concerns for the platform
Joint position feedback from dedicated sensor (not servo’s own!)
Safety issues to automatic cut of power on controller failure
Better adjustable tensors for belts Selection and installation of central
control unit (Embedded Linux) Selection and installation of the vision
unit (FireWire..?) Research concerns
Localized/distributed control algorithms Elementary Gait definition ...
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Hints for local control The difficult relation between planning and
stability opens the way to localised control Minimal dependence on planned variables Better adaptation to changing conditions (e.g., load, ground)
Force-based perception is the key issue:• Reaction forces• Joint torques / motor currents
What local control can do Accept a global directive and act locally based on an
associated rule. Example:
• Top order: keep standing immune to perturbations• Local rules: try to actuate the joints you control in order to
keep force balance (e.g., try to have a distribution of forces as uniform as possible on the foot area)
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Conclusions A highly versatile platform is possible to be built with
constrained costs and off-the-shelf components. The distributed control architecture has shown several
benefits: Easier development Easier debugging Provides modular approaches
• The generic local controller using piggy-back modules is a confirmation of the modularity
Local controller capabilities include the possibility of localised control based simply on local perception and global directives.
A prototype system has been built and the selected technological solutions ensure a platform for research
A huge field of research issues can be addressed, mainly on control, perception and other autonomous navigation matters.
UNIVERSITY OF AVEIRO, PORTUGALCentre for Mechanical Technology and AutomationInstitute of Electronics Engineering and Telematics
Author’s Short Biography
Vítor Santos is Associate Professor at the Department of Mechanical Engineering of the University of Aveiro He received his PhD from the University of Aveiro in 1994 …
His research interests include …
Filipe Silva is Assistant Professor at the Dept. of Electronics and Telecommunications of the University of Aveiro He received his PhD in Electrical Engineering from the University of Porto
in 2002; modelling and control of biped locomotion systems
His main research interests are centred in the areas of Humanoid Robotics and Healthcare Robotics
Tel: +351 234 370 531 Email: [email protected]: +351 234 370 545 http://www.ieeta.pt
Tel: +351 234 370 828 Email: [email protected]: +351 234 370 953 http://www.mec.ua.pt