AIAA YPSE Conference21 November 2008
A Method of Robotic Actuation using Control Moment Gyros
Presenter: Ian Livingston
AIAA YPSE ‘08
November, 21st 2008
AIAA YPSE Conference21 November 2008
Overview
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
• Introduction• What is a CMG• Reactionless Actuation• Joint Torques vs. Body Torques• Planar Robot Design• Simulation Results• Experimental Design (Functional Flow)• Hardware and GUI• Controller Design• Closed Loop Gimbal Control• Feed Forward Joint Angle Control• Video• Future Plans• Acknowledgements• Questions
AIAA YPSE Conference21 November 2008
Control Moment Gyros (CMGs)
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
Components:•Constant speed reaction wheel•Gimbal motor (positioned along g axis)
Applications:•Momentum Storage•Propellant-less Attitude Control
Advantages:•Low Power (100x)1
•Spaceflight heritage
1. Carpenter, Peck 2008
Equation for torque output
Equation for reaction wheel momentumhr = Irw·rw
AIAA YPSE Conference21 November 2008
Reactionless Actuation
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
CMG Arm from previous project team on the “Vomit Comet”
Reaction Forces from Mechanism
•Actuator Reaction Forces•Caused by direct-drive motors. To rotate an object the motor rotates the base object in the opposite direction.
•Inertial Reaction Forces•Caused by a spinning object not at the center of mass.
Advantages to Reaction-Less Actuation:
•Isolate subsystems
•Reduce dumped momentum to the basestructure.
AIAA YPSE Conference21 November 2008
Joint Torques Versus Body Torques
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
R21
R2 1
Joint Torques Body Torques
motor cmg
R
R2
•CMGs create body torques
•The motion of the arm remains the same
•Only the torque caused by the off center reaction force needs to be absorbed using body torques.
R2
AIAA YPSE Conference21 November 2008
Planar Robot Arm Design
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
Purpose:To create a CMG robot arm to demonstrate the advantages of body torques on space applications.
Design:
•Two or more link free floating CMG arms
•Air bearings to provide frictionless surface
•Use Scissored Pair CMGs to remove Gyroscopic effects and off axis torques
Previous work and Motivation:•Past teams built the reaction wheels for a CMG arm test
•Only open-loop results were obtained from zero-g tests
•This experiment was created to perform tests anytime
Photo: A. Soto
AIAA YPSE Conference21 November 2008
Scissored Pair CMGs
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
Advantages:•Eliminate off-axis torques
•Direction of torque is fixed
•No internal singularities
•Cancelation of unwanted gyroscopic effects
A A/G G /A N G /A A/N
G /A G /AA/N A/N
ˆˆ
ˆ
i igi ri
i
ri
i
i igi ri
ω ω ω
ω
I I ω gτ g
ω gI I ω ω h
Video: M. Peck
AIAA YPSE Conference21 November 2008
Simulation Analysis and Hypothesis1
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
Joint torque advantage
CMG advantage
From power simulation results:
•CMGs are better for reaching tasks
•Joint torques better for panning tasks
•Simulation to determine power properties of CMG arm•Utilized several set ups for links and properties•Main focus on one link and two link robot arms both in parallel axis and perpendicular joint axes.•Simulation assumes 0 initial and final velocities and accelerations.
D. Brown, 2008
AIAA YPSE Conference21 November 2008
Experimental Design (Functional Flow)
MATLAB GUI
Joint Angle
Start Control
MATLAB code
Wireless Belkin
Transceiver
Data, Graphs
Commands
Data
Computer
Control Voltage
PotentiometerData
Wireless Link
Wireless Belkin USB
Hub
CMG Robot Arm
USB DAQ Board
Reaction Wheels (2x)
Reaction Wheel
Speed Controller
Power Supply
Motor Controller
Gimbal Potentiometer
Joint Potentiometer
Gimbal MotorVoltsVolts
Gimbal Rotation
Volts
Volts
Power Supply
Power Supply
Power Supply Power Supply
Data
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
AIAA YPSE Conference21 November 2008
Hardware and MATLAB GUI Design
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
AIAA YPSE Conference21 November 2008
Controller Design
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
•Gimbal Angle is controlled by a PID closed loop control
•Joint Angle is controlled using a Simulink model with feed forward control
AIAA YPSE Conference21 November 2008
CL Gimbal Angle Control Analysis
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
Equations of motion for gimbal motor:
Transfer function for gimbal motor:
Root locus, Bode Plots and gains:
Gains:Kp= 3Ki = 1Kd = .1
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1-1.5
-1
-0.5
0
0.5
1
1.5Root Locus
Real Axis
Imag
inar
y A
xis
-150
-100
-50
0
50
100
Mag
nitu
de (
dB)
10-1
100
101
102
103
104
105
106
-180
-135
-90
-45
0
Pha
se (
deg)
Bode DiagramGm = Inf dB (at Inf rad/sec) , Pm = 20.7 deg (at 1.1 rad/sec)
Frequency (rad/sec)
AIAA YPSE Conference21 November 2008
CL Gimbal Angle Control Results
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
2 4 6 8 10 12 14 16 18 20-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6Linear Simulation Results
Time (sec)
Am
plitu
de
AIAA YPSE Conference21 November 2008
Feed-forward Control Design
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
•System is non-linear•Small angle approximation was not assumed since can rotate up to 70°
Relationship between Joint angle and gimbal angle:
Current issues with Feed-Forward:•The runtime of the feed forward Simulink block is approximately .11 seconds. •This would limit the control system by 10 data points•At maximum voltage this is equivalent to 30 degree rotation
AIAA YPSE Conference21 November 2008
Video of CMG robot arm
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
AIAA YPSE Conference21 November 2008
Future task, test, and Goals
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
Current Issues:•Joint angle control is not fully functional•No support for multi-links•Air canisters are currently leaking
Planned Tests:•Full systems test using feed forward control•Evaluation of power consumption versus joint angle control
Identified Improvements:•Characterize noise in potentiometer and build LQG control•Replace existing reaction wheels with smaller and faster COTS wheels•Reduce the size of the supporting arm and structure•Remove chain and replace with gears
AIAA YPSE Conference21 November 2008
Acknowledgements
Outline:-Introduction-What is a CMG-Reactionless Actuation-Joint Torques vs. Body Torques-Planar Robot Design-Simulation Results-Experimental Design-Hardware and GUI-Controller Design-CL Gimbal Control-Feed Forward Control-Video-Future Plans-Acknowledgements-Questions
•Daniel Brown, PhD. Candidate, Aerospace
•Dr. Mason Peck
•Space Systems Design Studio
•Cornell CMG team
1. DARPA SUMO spacecraft with CMG arms
AIAA YPSE Conference21 November 2008
Questions?