KDC Arm Project John Kua Kathryn Rivard Benjamin Stephens Katie 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 TTL SerialTTL PWM TTL / Analog

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

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.