Robotic Platform for Appearance Editing

C. D. Tharindu MathewAdvisor: Prof. Daniel Aliaga

Appearance Editing

● Illuminate an object using digital projectors, so that its appearance is visually altered

Source: http://wiki.cs.purdue.edu/cgvlab/doku.php?id=projects:virtual_restoration

Setup Details - Robots

Wheeled mobile robots equipped with ● Raspberry Pi with HDMI output and wifi dongle● Micro Projector● Infrared LED pattern on top● Control circuit to drive motors

Setup Details - Control Table

● Table with checkerboard pattern● Overhead camera with infrared filter

Setup Details - Control Program

● Receives input from overhead camera● Issues commands and pose information to robots● Calibration of camera and projector

Contribution

● Robots, Control table - Luis Rodrigo, Control Program - Prof. Aliaga

● Robot control program existed, written in Python● Re-wrote the robot control program in a more structured

manner with reliable execution

wiringPi

● C Library that allows to control GPIO pins● Allows to generate software based PWM signals● High performance in benchmarks - Possible to generate

6.9 MHz signal

Source: http://codeandlife.com/2012/07/03/benchmarking-raspberry-pi-gpio-speed/

Development Environment

● Raspberry Pi runs Raspbian 32-bit● Eclipse allows to configure different compilers● Windows Batch script to deploy into robots

Initial Attempt

● Wrote a control loop that does the following:o Rotate towards destination pointo Move at constant speed for 2so Repeat

Video - Initial Attempt

https://www.youtube.com/watch?v=iLXbehabnwY

Control Theory

Source: http://en.wikipedia.org/wiki/File:Feedback_loop_with_descriptions.svg

Error and Input w.r.t. the Robotic Platform

● Measured Output - (xc, yc)● Measured Error - (x, y, ϴ)

● Output - (vl, vr)

Proportional-Integral-Derivative (PID) Controllers

Sources: http://www.oemheaters.com/t-temperature-controller-styles.aspx, http://en.wikipedia.org/wiki/PID_controller

Model Equations

Video - Attempt after integration of PID Controller

https://www.youtube.com/watch?v=iLXbehabnwY

Velocity cut offs

● Maximum velocity operates at 30%● Minimum velocity is 10%● Ratio between vl and vr are considered when one value

hits maximum

Tuning the PID Controller

● To accommodate the table size, more rotation is needed compared to translation

● Use 66x more Kp and Ki values for output ϴ (0.3 vs 200)

Video 3 - Tuned PID Controller

https://www.youtube.com/watch?v=RjGPhbkbHsQ

Projector Calibration

● Uses overhead camera to calibrate Projector using Tsai’s method

● Then, create image to project based on the

image→world coordinates

Results

● Reliable movement of robot● Projector error of 3mm

Future Work

● Increasing projector accuracy to sub-millimeter range● Increase motion precision to millimeter range

Thank You

Questions?