TAGRR

 

 

 

I. Introduction II. Purpose III. Theory of Operation IV. Summary V. Future Applications

Appendix A VI. Parts and Costs VII. Labor Costs

Appendix B Figure 1. TAGRR Physical Diagram Figure 2. TAGRR Main Unit Figure 3. TAGRR Transmission Unit Figure 4. TAGRR Block Diagram

 

I. Introduction

In 1995 alone, Santa Clara County spent more than two million dollars to

get rid of the county's nagging problem: graffiti. Taggers, as they

are called, spray paint on freeway signs, walls, bridges, and buildings.

The graffiti they leave behind not only degrades the appearance of

structures, but also poses a safety hazard to the general public.

Although programs are in place to reduce the graffiti around Santa

Clara, the cost of maintaining our streets graffiti-free remain

strikingly high in our dire economic times. Taxpayers have had

enough; something must be done.

The Totally Automated Graffiti Removal Robot (TAGRR) is a self-

propelled, graffiti-sensing and graffiti-removing robot. It

requires no outside human assistant except for transporting

it from long distances. The TAGRR moves alongside a wall,

its sensors searches for graffiti, and sprays only the

affected area when it does detect graffiti. This intelligence

reduces the costs in paint. When it has finished its task, it

automatically sends out a radio signal to CalTrans to be picked

up. A single TAGRR in its fully realized version would be able

to clean an entire wall in a fraction of a time than its

human counterpart. Being a robot, the TAGRR does not require

costly human benefits as required by law, and it pays for

itself in the long run. In general, the TAGRR does its job

efficiently, effectively, and cheaply.

The TAGRR consists of five major components: the Graffiti-Detection

Unit (GDU), Control Circuitry (CC), Spay Painting Unit (SPU),

Drive Unit (DU), and the Transmission Unit (TU). The GDU's main

corresponding output current proportional to the reflected light at

the input. This current is then feed to a resistor to produce the

desired output voltage. A white surface produces a relatively

high voltage at the emitter-biased output of the MFOD73. A dark

surface, on the other hand, produces a relatively low voltage at the

emitter output. It is then amplified to produce a TTL compatible

output voltage.

This TTL compatible voltage is then feed into the CC. The CC

consists of a 7408 AND gate and a 7410 NAND gate. The 7408 AND gate

produces a true TTL output voltage. TTL logic, HIGHs and LOWs, causes

steeper rise and fall times that are desirable for the SPU. Voltage at

the output of the AND gate branches into two directions. One goes

directly to the buffered input of the SPU while the other gets

inverted through the NAND gate and goes to the other buffered input

of the SPU. This setup acts as a push-pull transistive circuit. The

SPU mainly consists of two TIP-122 Darlington transistors each

having an independent +12 collector voltages, and their purpose is to

drive the DC Motor Solenoid (DMS).

The DMS activates the spray gun. Only one TIP-122 can be activated

by the CC at any time while the other is shorted. The DMS is connected

to the collector of both TIP-122s. The polarities change as one TIP-122

gets saturated and the other gets cutoff which causes the DMS to push

or pull the actuator shaft depending on the input at the GDU. When the

GDU detects a dark surface, the DMS pushes down on the spray gun,

thereby releasing the paint. The DMS arm pulls up only if the GDU

detects white surfaces.

The DU consists of the DC motor and another MFOD73 to detect the

end of the wall. Once the DU detects a predetermined light intensity

at the end of the wall, it causes the motor to reverse slowly and stop,

thereby stopping the whole unit. After the unit has stopped

completely, it activates the TU which is an AM modulator that would

transmit a pulse signal to CalTrans.

The TAGRR was intended to be used in removing graffiti effectively.

According to the results, the TAGRR performed as expected.

Limitations are there, but the limitations can be overcome by

using better sensors, fast switching circuits, and so on. Some of the

limitations are present because of using DC to power the system

instead of AC. With AC, many of the limitations such as switching could

be eliminated. Furthermore, AC could be use in conjunction with a

generator to produce a cost-effective system. Notice that this system

is only a prototype.

TAGRR is a system that can expanded into more uses by changing the

modular parts of the original system. For example, it could be

converted to a windshield wiper system by replacing the SPU with a

brush unit. Enhancements are also possible. By attaching a

helicopter to the unit combined with remote control, a complete

versatile system evolves. Another enhancement would be to use a

computer system to record the original color of an object such as a

wall and control the nonlinear speed of the motor to paint only the

graffiti-ridden part of the object. With color sensors, various

colored objects would be applicable as opposed to monochrome objects

only.

VI. Parts and Costs

The following is a list of the parts used for the TAGRR system

and their approximate prices:

VII. Labor Costs

The following is a list of labor costs including total hours spent

on the project and hourly rate for each employee.

The total of hours spent on this project was 69 hours. The grand

total of the TAGRR project is $1460.75.

Figure 1. TAGRR Physical Diagram




Figure 2. TAGRR Main Unit




Figure 3. TAGRR Transmission Unit




Figure 4. TAGRR Block Diagram