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KDC Arm Project
John KuaKathryn Rivard
Benjamin StephensKatie Strausser
Outline
• Overview
• Mechanical Design & Fabrication
• Electrical & Software
• Simulation & Control
• Demo
• Future Work
Overview
• Goal: Design and control a novel dynamically balancing manipulator
• Motivation: Assistive robot manipulator to be mounted on friendly household Segway robot
• Typical Task: Pick up objects from cupboard, open doors, take out the garbage
Mechanical
• Started with dynamic analysis to decide system specifications and parameters
Mechanical
• Designed mechanism in Solidworks CAD
• Easy to use aluminum extrusions
• Single linear actuator moves counterweight to balance arm
• Ball bearings support screw drive assembly
Electrical• Sensors
– Joint encoder (500 CPR)– Screw encoder (2048 CPR)– Accelerometer (3-axis)– Rate gyro (2-axis)– Limit switches (SPST)
• Motor control– Serial commands – 24V/10A max
• Gripper control– Standard servo PWM
• Microcontroller– ARM7TDMI-S– 60 MHz
Software
• Microcontroller– 100 Hz main loop
• Motor control input/output• Servo control• Data logging to serial port
– 50 kHz sensor polling– 500 Hz servo PWM
output
• PC Side– Controller (100Hz)– Data logging to file
PC
Microcontroller
Motor Controller
Gripper Servo
Sensors
RS
-232
TT
L S
eria
l
TT
L P
WM
TT
L / A
nalo
g
Software
• Kalman Filter– Estimated states – tilt and gyro bias– Sensor inputs at two speeds
• 2 kHz rate gyro• 50 Hz accelerometer
– Gyro primary sensor• Drifting bias
– Accelerometer to estimate bias• Noisy, captures more than pure rotation
Software – Kalman Filter
• Process update (2 kHz)
• Measurement update (50 Hz)
Software – Kalman Filter
0 1 2 3 4 5 6 7 8 9 10-40
-30
-20
-10
0
10
20
30
Time (s)
Tilt
(D
eg)
Shoulder Position
Encoder Tilt
Accelerometer Tilt
Onboard KF Tilt
Software – Kalman Filter
0 1 2 3 4 5 6 7 8 9 10-300
-250
-200
-150
-100
-50
0
50
100
150
200
Ang
ular
Vel
ocity
(D
eg/s
)
Time (s)
Shoulder Velocity
Encoder Derived Velocity
Compensated Gyro OutputEstimated Gyro Bias
Simulation & Control
• Problem: Move counterweight to balance arm independent of gripper weight
• Key Idea: Counterweight moves slowly -- must plan ahead!
• Solution: – Plan a trajectory from an initial state to the arm set
point– Use acceleration to determine the counterweight set
point.
Simulation Results
Experimental Results
DEMO!
Future Work
• More sophisticated control: Input shaping, MPC, etc.
• Optimize counterweight mass/travel
• Shoulder joint actuation
• Joint shape iteration (yoking joint)
• Increase robustness for object balance
• Interface to Segway
Effect of a yoke: Balanced torques
The End
• Special thanks to Garth Zeglin for helping us design the arm.