Force Control of a Duct Cleaning Robot Brush

using a Compliance Device

Wootae Jeong

, Seung-Woo Jeon

, Duckshin Park

and Soon-Bark Kwon

Eco-Transport Research Division, Korea Railroad Research Institute, Gyeonggi-do, Uiwang, Korea

Department of Virtual Engineering, University of Science and Technology, Daejeon, Korea

Keywords: Compliance Device, Service Robot, Air Duct Cleaning, Air Quality, Force Control.

Abstract: Conserving clean air and removing contaminants and particular matters accumulated in the ventilation

system of the subway stations are key issue for high air quality and green environment. Accumulated

various pollutants at inner duct surface can cause secondary air contamination and injure subway

passengers’ respiratory system and health. In fact, periodic duct cleaning works can improve indoor air

quality, but cleaning entire ventilation system takes high cost and manpower. This study proposes a newly

developed duct cleaning robot to provide autonomous air duct cleaning. In addition, effective cleaning

method with an automated robot device is developed. In particular, the new duct cleaning robot has

functionality that cleans four sides of inner duct surface simultaneously with a constant pressure by using a

force compliance brush. Control method with the compliant device has also been analysed. The proposed

design of autonomous duct cleaning robot is expected to save the operating cost of subway ventilation

system and sustain clean indoor air quality by providing easier and faster cleaning tools.

1 INTRODUCTION

The main purpose of the ventilation system and air

duct is to supply fresh air into closed spaces such as

buildings and subway stations where people work

and spend most of their daily hours. The air duct and

ventilation system controls various air flows, i.e.,

outdoor air, supply air, return air, and exhaust air as

depicted in Figure 1. The ventilation system also

consists of mechanical components such as dampers,

fans, filters, and duct terminals. Various particulate

matters are initially filtrated with particle filters

installed at the side of the supply air duct. The filters

commonly used, however, are insufficient to prevent

the entrance of all the particulate matters from

outdoor air into the duct. Therefore, transported dust

and other impurities are accumulated at the duct

surface inside the ventilation system. Accumulated

dust inside air duct may also originate from the

facility construction phase or from ventilation duct

installation (Pasanen, 1998).

To provide fresh and clean supply air through the

ventilation system into the closed space such as

subway stations, eliminating source for the

pollutants and contaminants is the most cost

effective than cleaning and replacement of the air

duct. However, duct cleaning is essential for

maintenance after completion of the ventilation

system installation. Many countries have existing

regulation and guideline for ventilation system

cleaning intervals and specific guidelines of

ventilation system cleanliness (FiSIAQ, 2001). A

few countries do not still provide legal regulation,

which makes air quality from the ventilation system

severely contaminated.

Figure 1: Air duct and ventilation System.

In this paper, various duct cleaning technologies

are introduced and types of contaminants are

analysed. Based on the mechanical brushing

technology, a new autonomous air duct cleaning

372

Jeong W., Jeon S., Park D. and Kwon S..

Force Control of a Duct Cleaning Robot Brush using a Compliance Device.

DOI: 10.5220/0004119703720376

In Proceedings of the 9th International Conference on Informatics in Control, Automation and Robotics (ICINCO-2012), pages 372-376

ISBN: 978-989-8565-22-8

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

robot has been designed to improve the cleaning

efficiency and overcome restrictions of manual duct

cleaning. In particular, in order to control constant

brush pressure on the duct surface, a simple force

compliance device is designed and installed at the

brushing arm, which enables consistent cleaning

operation despite of irregular duct surface quality.

2 CLEANING TECHNOLOGY

The ventilation system can be contaminated and

acted as another source of pollutants, such as

microbe, chemical compounds or odours, particulate

matters. Accumulated dust and particulate matters

inside duct can stick to the inner surface of duct and

scatter by air stream of the air duct. Several cleaning

technologies can be used to remove the dust and

other contaminants effectively from the duct surface.

2.1 Contaminants in Duct

The estimated annual accumulation rate for dust in

commercial supply air ducting is normally set at

1g/m

. However, an average accumulation level in

supply air ducts of building occupied less than a year

was 5.1 g/m

(Pasanen, 1998) while dust level in

new constructions was measured as high as 4.9 g/m

(Holopainen et al., 2002). In general, if dust

accumulation on an inner duct surface exceeds

2g~5g/m

upon the class of ventilation system the

duct has to be cleaned. Amount of dust accumulated

inside duct is related to the types of facility,

complexity of duct and its components and age of

building. In addition, dust concentration is affected

by factors that interrupt air flow of duct such as

surface roughness, air velocity, humidity, number of

dampers and diffusers installed.

Accumulation of dust also provides suitable

conditions that microbes, bacteria and other

microorganism can propagate. In fact, it has been

reported that 400 times of penicillium and 9.5 times

of aspergillus exists within 1 micro particulate

matter (Morey, 1988). In addition, amount of fungi

in contaminated indoor air is 10 times higher than

that of outdoor air. Many other particulate matters

accumulated at a duct terminal may cause secondary

infection or contamination of indoor air through the

air supply duct.

2.2 Cleaning Technologies

The air duct cleaning methods can be either dry or

wet (HVCA, 1998). The most commonly used dry

duct cleaning methods are mechanical brushing,

compressed air cleaning and vacuuming. Dry

cleaning methods use a rotating brush, a powerful air

jet or a suction force to detach the dust from the duct

surface mechanically. The loose dust is carried out

of duct by airflow. Wet cleaning methods include

water jet or chemically sterilizing process to

eliminate microorganism and bacteria. However, wet

cleaning methods are seldom used to clean air ducts

because the ductworks are not normally watertight.

To remove accumulated dust and oil in duct,

mechanical brushing is faster and more effective

than compressed air cleaning. Cleaning methods are

summarized in Table 1.

Table 1: Summary of duct cleaning techniques.

Cleaning Techniques

Description

Dry

method

Mechanical

brushing

A brushing or mechanical action is used to

dislocate dust from surfaces and transferred

to a vacuum collector. The most commonly

used is the rotating brushes.

Compressed

air cleaning

Dust is dislodged from surfaces using

airflow movement (via air nozzle) and

collected using a vacuum collector.

Vacuuming

Suction and brushing using a brush head to

transfer dirt to a collection point.

Wet

method

Hand

washing

Cleaning components surfaces by hand using

tools such as brushes, sponges and a source

of water with a cleaning agent.

Water jet

spray

Liquid solutions are sprayed or wet-fogged

to adhere, bond, or fibre- fixed particles that

were not removed mechanically.

Chemical

disinfection

The use of biocides and sealants to coat and

encapsulate duct surfaces. Some duct

cleaning contractors introduce ozone as part

of the disinfection process.

Figure 2: Duct cleaning with mechanical brushing and

robot.

In this study, we have focused on mechanical

brushing method with autonomous cleaning robot to

improve cleaning efficiency for all types of

contaminants. As illustrated in Figure 2, the air duct

cleaning robot system also utilizes the push-pull

Force Control of a Duct Cleaning Robot Brush using a Compliance Device

373

technique; the rotating brush removes dust and

debris from the inner surface of the duct. The dust is

then drawn into a negative collector. Compressed air

is often used to push the dust and debris.

3 DESIGN OF A DUCT

CLEANING ROBOT

Increased interests in air duct cleaning technology

stimulate development of various duct cleaning

robots. Most of duct cleaning robots is based on the

dry cleaning method with mechanical brush.

As an example, the Articulated Nimble

Adaptable Trunk (ANAT) robot has been developed

to clean and inspect HVAC ducts. The

ANATROLLER ARI-100 duct cleaning robot rolls

on tracks or wheels and will continue to operate

even if flipped upside down. It is composed of two

modules containing the air jet, lighting and camera

rotates through 180 degrees, which allows the robot

to change its shape to get around or over obstacles

(Robotics Design Group). However, the ARI-100

still needs manpower to operate.

The XPW-series duct cleaning robot is of height

adjustable rotary brush and rotating camera for

inspection and remote control. Its rotary brush

mounted at machine bed is oscillatable within a

prescribed angle range in a vertical direction

(Hanlim Mechatronics Co. Ltd.).

Recently developed cleaning robots can be fitted

with spinning brushes, directional air nozzles and

whips, sampling devices, and spraying attachments

for spraying sanitizing solutions for various coatings.

Figure 3: Duct cleaning robot with rotary brush arms.

In this research, the duct cleaning robot designed

will be unique in its functionality and usability. The

robot has equipped with adjustable brush arms at

which rotary brushes are attached to clean four duct

surfaces autonomously. In addition, a force

compliance device was designed and installed at the

end effector of the robot brush arm. Since the

compact compliance device can recognize the

pressure between brush and duct surface, the robot

brushes can clean up the surface as a constant

pressure even if the cleaning surface is of

irregularity.

Figure 4: Brush and compliance device.

3.1 Mobile Platform and Arm

A newly developed duct cleaning robot is depicted

in Figure 3. The robot consists of a base body,

continuous tracked wheels, a camera module, LED

light and two brush arms; upper and low arm. Six

motors have been used to provide proper torques for

ductworks. The rubber-based tracked wheel was

selected not only to decrease slippage between

driving wheels and duct surface, but also to reduce

weight of the robot platform (Wang et al., 2006).

The lower brush arm is attached at the front of

platform body and the upper brush is located at the

end effector of the upper arm. The upper arm with

R-R-P joints is height adjustable for handling

various duct sizes.

The compact force compliance device is installed

between two cylindrical rotary brushes at the end of

the upper arm. The compliance device consists of

two springs and linear sensors to read deflection of

the spring. The two springs are connected each other

at the end point to read two directional force. The

brush and compliance device are depicted in Figure

3.2 Force Control with a Compliance

Brush

The compliance device attached at the end of the

upper arm enable robot arm to detect force between

brush and surface of duct, which make it possible to

control the constant pressure. Figure 5 presents a

model of force compliance brush illustrated in

Figure 4. Figure 5(a) represent a model when the

brush is contacting only with the upper surface of

duct, and Figure 5(b) shows that the brush is

ICINCO 2012 - 9th International Conference on Informatics in Control, Automation and Robotics

374

contacting at two points, i.e., upper and side surface

of duct. During the brush is under pressure, normal

force and tangential force are acting on the

compliance device.

(a) (b)

Figure 5: Force compliance brush models; one point

contacting model(a) and two points contacting model(b).

The force acting on the compliance device can be

simply calculated by using spring constant K, which

is given by

aaa

xKF 

(1)

bbb

xKF 

(2)

where Δx is a spring deformation and K is a spring

constant. The two spring constants are identical

when same spring is used. It should be noted that the

deformation of spring (Δx) is a nonlinear because

the stiffness of brush is, in general, empirically

derived and deflection of brush is also affected by

many factors such as bristle modulus, the number of

tufts, and the trim length of bristles (Rawls et al.,

1990). Therefore, value of the Δx has to be found by

calculating the stiffness of brush empirically.

Assuming that 2 α is the angle between two

springs each other, the forces acting on the brush

are calculated as



cos)(coscos

babau

FFFFF 

(3)





sin)(sinsin

abab

FFFFF



(4)

where



is a normal force action on the brush

from the upper surface. The friction force is written





The dynamic friction coefficient



can be

derived from Eq. (3) and (4) and given by





tan

)(

cos)(

sin)(













(5)

Therefore, normal force acting the brush can be

controlled by using robot arm parameters, i.e.,

translation length d and rotation angle θ in case of

one point contact.

When the rotary brush is contacting at two

surfaces as shown in Figure 5(b), the force

equilibrium equation from Eq.(3) and (4) can be

rewritten as

Horizontal:



sin)(

absuu

FFFF 

(6)

Vertical:



cos)(

bassu

FFFF 

(7)

where

is a normal force between the brush and

side surface and



is a dynamic friction coefficient

at side surface of duct.

Assuming that dynamic friction coefficients are

identical,

and

can be simplified as

sin)(cos)(











abba

FFFF

(8)

)1(

sin)(cos)(











abba

FFFF

(9)

where





Consequently, the cleaning pressure of robot

brush can be constantly controlled with an actuating

arm at both models.

3.3 Control Scheme of Robot System

In addition to control the cleaning pressure of the

upper arm brush, it is required to control the driving

motion of the mobile platform. The mobile platform

can be either controlled by joystick or automatically

by using ultrasonic sensors to adjust position and

orientation of the robot platform. The overall control

scheme is shown in Figure 6.

The CCD camera and LED light enables

operators to monitor and control the system

manually if needed. Thus, the duct cleaning robot

can be controlled automatically or manually through

the user interface system.

Figure 6: Control scheme of the duct cleaning robot.

Force Control of a Duct Cleaning Robot Brush using a Compliance Device

375

4 CONCLUSIONS

In this study, a new type of duct cleaning robot has

been designed and prototyped. In particular, the

robot has functionality that cleans four sides of inner

duct simultaneously with a constant pressure by

using a force compliance device. For more dedicated

control of brush pressure, the stiffness of brush

should be empirically achieved. The adjustable arm

brush can make it possible to use in different size of

ducts.

However, there are still more room for

improvement, especially on the autonomous system.

In a real ductwork, there are many components at

the inner duct such as dampers, fans, joints and

curves that make it difficult to operate the robot

consistently and autonomously. Therefore, more

intelligent operating system has to be implemented

to improve the cleaning process effectively. The

developed prototype robot will be continuously

upgraded and tested at the test-bed of air duct

terminal.

ACKNOWLEDGEMENTS

This research was carried out as a part of the subway

air duct cleaning robot project (Eco-Innovation, No.

E211-40002-0003-0) funded by the Ministry of

Environment in Korea.

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