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Applied Robotics: Software Architecture, Development, & Integration David M. Huhn Student Scholarship Day April 10, 2002 Background & Introduction GROMIT: Autonomous, Fire-fighting Robot Concept, Initial Hardware and Software: Summer Research Project Architectures Expanded:

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Applied Robotics:

Software Architecture, Development, & Integration

David M. Huhn

Student Scholarship Day

April 10, 2002


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Background & Introduction

GROMIT: Autonomous, Fire-fighting Robot

Concept, Initial Hardware and Software:

Summer Research Project

Architectures Expanded:

Class Projects, free time, etc.

Basic Abilities:

Motor Control

Proximity Detection

Flame Detection

Flame Suppression

What was done?

Higher-level software development

Software-hardware integration

Why was it developed?


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Robot Competition – Goals & Objectives

“...to build a computer controlled Robot that can move through a model floor plan structure of a house, find a lit candle and then extinguish it in the shortest time...”

“...meant to simulate the real-world operation of a Robot performing a fire protection function in an actual home...”

“...the real goal of the contest is to advance Robotics technology and knowledge both in the competing individuals and in the world in general”

- Taken from Trinity College Robot Contest Site



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Hardware Architecture

Main Board

Implemented

Peripherals

Communication

Bus

Main Board:

System Microcontroller – Overall flow of execution

Memory – Program and data storage

Expansion slots – Peripheral Devices (specific functionality)

Implemented Peripherals

Power Board – provides for all power requirements of systemMotor Board – control of all motors (positioning, fire-extinguishing)Infrared Board – control of three individual proximity sensorsFlame Board – control of flame sensor


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Software Architecture

Low-Level Functions: Control hardware at most basic level

Motor Driver – Rotate clockwise, rotate counter-clockwise, stop, etc.

Infrared Driver – Pulse emitter, read detector

Flame Driver – read detector

Intermediate Functions: Utilize hardware drivers to perform simple function

Forward movement, acceleration, etc.

Obstacle detection

Flame detection

High-Level Functions: Integrate multiple Intermediate functions to complete goal:

Accelerate to full speed, move forward until a wall is detected, then slowdown and stop.

Rotate slowly while polling the flame sensor, stop if a flame is detected, turn on the fan.


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Required Abilities

Reliable Movement/Positioning

Does the robot move where it should?

Is a 90 Deg turn really 90 Deg?

Does the robot move in a straight line?

Is it repeatable?

Proximity Detection

Is an obstacle present?

Where is it located?

Flame Detection

Is a flame present?

How close is it?

Simple abilities often require complex software

Movement...


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Reliable Movement

Why is it important?

Robot knows present location and orientation within the maze

Why is it difficult?

Non-identical components:

Do both motors turn at the same rate?

Are the wheels both perfectly round?

Other factors to consider:

Is the surface smooth?

How much friction are the stabilizers subject to?

How can it be achieved?

Software compensation:

Multiple speeds (30 different speeds)

Acceleration profiles

Sensor correction


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Reliable Movement – Original Motor Software

Problem: Not enough speeds:

Acceleration not smooth

Movement not straight –both motors set to same speed

Original Implementation:

Single command (4 bits of information)

5 – forward motion

1 – reverse

Solution: Build on existing architecture

Multiple commands:

30 – forward motion

30 – reverse motion

Problem fixed?

Yes, and no...more distinct speeds, new problem developed...


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Reliable Movement – New Motor Software

Problem: Movement not smooth on speed changes:

Smooth movement at any of the 30 speeds, provided robot stays at that speed.

Accelerating up or down produces “jerky” movement

Inexact Pulse-Width-Modulation to drive motors, motors were disabled on speed changes.

Solution: Rewrite original motor driver

Interrupt driven, Pulse width modulation for motor driver.

30 speeds (40% Positive Duty cycle and 100% Positive Duty cycle)

Motors no longer disabled during transition

Problem fixed?

Yes, and no...more distinct speeds, however, communications between system microcontroller and peripheral microcontroller broken.


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Reliable Movement – Interrupt-based Software

Problem: Interrupt service routine incompatible with existing communications

Motors did not recognize commands sent to it because they were not received properly.

Solution: Rewrite the communications interface

Short delays added to give peripheral microcontroller time to correctly read the value being

transmitted.

Problem fixed?

Yes, and no...more distinct speeds, better movement, however not repeatable.


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Reliable Movement – Sensor Correction

Problem: Movement not always straight(repeatable):

Acceleration profile and additional speeds greatly improved accuracy...

Imperfect hardware still causing occasional crooked movement

Solution: Supplement multiple speeds with sensor correction

Sensor sensitivity adjusted to detect maze walls

Dynamic changes in motor speed when a sensor reports a hit

Problem fixed?

Yes, reliability of movement has been greatly increased.


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Software Development

Problems in software at any level can cause the entire system to fail

Problem with code at one level might require code at another level to be rewritten

Software development and integration is an iterative process



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