a_series of pneumatic glass-wall cleaning robot

Research article

A series of pneumatic glass-wall cleaningrobots for high-rise buildings

Houxiang Zhang and Jianwei Zhang

University of Hamburg, Hamburg, Germany, and

Wei Wang, Rong Liu and Guanghua ZongBeiHang University, Beijing, People’s Republic of China

AbstractPurpose – This paper presents the design of climbing robots for glass-wall cleaning.Design/methodology/approach – A systemic analysis of the basic functions of a glass-wall cleaning system is given based on the research ofworking targets. Then the constraints for designing a glass-wall cleaning robot are discussed. The driving method, the attachment principle, mechanicalstructure and unique aspects of three pneumatic robots named Sky Cleaners follow. In the end a summary of the main special features is given. All threeclimbing robots are tested on site.Findings – Our groups spent several years in designing and developing a series of robots named Sky Cleaners which are totally actuated by pneumaticcylinders and sucked to the glass walls with vacuum grippers in mid-air. It was found that they can meet the requirements of glass-wall cleaning.Research limitation/implications – The air source, cleaning liquid and control signals should be provided by the supporting vehicle stationed on theground. Even if the robots are intelligent, the suitable working height is below 50 m because the weight of the hoses has to be taken into account whenthe robots work in mid-air.Practical implications – The cleaning robotic systems can avoid workers presence in a hazardous environment and realize an automatic cleaning,furthermore reduce operation costs and improve the technological level and productivity of the service industry in the building maintenance.Originality/value – Sky Cleaner robots can move and do cleaning on the plane glass wall or the special curve wall with a small angle between theglasses. The first two prototypes are mainly used for research and the last one is a real product designing for cleaning the glass surface of ShanghaiScience and Technology Museum.

Keywords Robotics, Motion, Cleaning, Buildings

Paper type Research paper

1. Introduction

The last few years had witnessed a strong, renewed interest inclimbing and walking robotic technologies. Climbing robotsare useful devices that can be adopted mainly in three fields:1 Reliable non-destructive evaluation and diagnosis in

hazardous environments such as the nuclear industry,the chemical industry and the power generation industry(Long and Muscato, 2004; Briones et al., 1994).

2 Welding and manipulation in construction industry,especially of metallic structures such as in bridges,shipping, off-shore industries and buildings’ skeletonsusually involve a very high number of dangerous manualoperations (Armada et al., 1998).

3 Cleaning and maintenance for high-rise buildings(Elkmann et al., 2002; Liu et al., 2003).

Now there are a large number of high-rise buildings with

curtain glass walls in modern cities. Figure 1 shows the typical

environments for cleaning robots. These external cladding

walls require constant cleaning which is presently typically

carried out using a costly, permanent gondola system hanging

from the roof of the building. This solution is highly

expensive, quite dangerous in mid-air.There are several motivating factors for developing a

climbing robot for glass-wall cleaning. A robotic system can

relieve workers of their hazardous work and make the

automatic cleaning of high-rise buildings possible.

Additionally, it can improve the technological level and

productivity of the service industry. Wall cleaning and

maintenance of high-rise buildings is becoming one of the

most appropriate fields for robotization due to its current low

level of automation and lack of uniform building structure.A number of different kinds of kinematics for motion on

smooth vertical surfaces are presented over the past decade.

The robots with multiple-legs kinematics have a lot of degrees

The current issue and full text archive of this journal is available at

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Industrial Robot: An International Journal

34/2 (2007) 150–160

q Emerald Group Publishing Limited [ISSN 0143-991X]

[DOI 10.1108/01439910710727504]

These projects were supported by “Hi-Tech Research and DevelopmentProgram of China”. Sky Cleaner 2 was also based on the collaborationwith City University of Hong Kong.

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www.emeraldinsight.com/0143-991X.htm

of freedom. This kind of robots uses vacuum suckers and

grasping grippers for attachment to the buildings. The robot

ROMA (Abderrahim et al., 1991) is a multifunctional self-

supported climbing robot which can travel into a complex

metallic-based environment and self-support its locomotion

system for 3D movements. Generally, this kind of robot’s

construction and control is very complicated, and does not

offer the high efficiency and simple operation required by a

wall cleaning robot (Luk et al., 2001).The prototypes with the wheeled and chain-track vehicle

are usually portable. The adhesion used by this kind of robot

is negative pressure or propellers, therefore the robots can

move continuously. One robot (Liu et al., 2000) has a pair of

wheels actuated by electrical motors in its negative pressure

chamber, so that it can move on the wall flexibly. Even if this

kind suction is not sensitive to a leakage of air, the negative

pressure is not good enough for the safe and reliable

attachment to the vertical surface when the robot crosses

window frames. A smart structure with two linked-track

vehicles was proposed (Wang and Zong, 2001). The structure

can be reconstructed so that the robot can move between

surfaces with an angle of 0-908. A kind of wall-climbing robot

using the propulsive force of propellers is presented in Japan

(Nishi and Miyagi, 1993). It is very light but the noise

generated by propellers is too loud to use on glass walls.SIRIUSc (Elkmann et al., 2002) is a walking robot for the

automatic cleaning of tall buildings and skyscrapers. The

robot can be used on the majority of vertical and steeply

inclined structure surfaces and facades. However, it has to be

positioned sideways by the trolley on the top of the roof as it

cannot move sideways automatically. The other kind of robot

was developed for the Leipzig Trade Fair. It is the first facade

cleaning robot for vaulted buildings worldwide. Because of

the building’s unique architecture, the robot is a very

specialized system and is not modularly-designed.Since, 1996, our groups have been developing a family of

autonomous climbing robots with sliding frames for glass-wall

cleaning. The eventual goal is to design a dexterity, intelligent

cleaning robotic system which can be used on different

buildings and meet the requirements of real application.This paper is organized as follows: in Section 2, the

constraints and the requirements for designing a glass-wall

cleaning robotic system are discussed. Then Section 3

presents an overview of three robotic systems. The

individual mechanical structure and unique aspects are

introduced in detail. The pneumatic system has the

characteristic of nonlinearities which make precise position

control difficult to achieve. So the different position control

strategies are studied in Section 4. At last a summary of the

main special features of the three cleaning robots is given as a

conclusion.

2. Requirements for the glass-wall cleaningsystem

2.1 Constraints from the working environment

Glass wall is a new operational target for a climbing robot. Itis a kind of external decoration construction which is made upof glass planks installed into metal components. There arefour kinds of glass curtain walls on high-rise buildings:1 exposed framing glass curtain wall (Figure 2(a));2 semi-exposed framing glass curtain wall (Figure 2(b));3 hidden framing glass curtain wall (Figure 2(c)); and4 full glass curtain wall (Figure 2(d)).

Even in the case of glass walls with a special curve, each pieceof glass is still a plank with a regular shape which is suitablefor robotic work. From a global point of view, a special curveshape is just because each glass is connected to theirsurrounding glasses at a small angle. But there are somewindow frames and seals between the glass planks whichbecome obstacles for cleaning. These boundaries of theplanks destroy the consistency of the working areas.The climbing robot has to be safely attached to the glass

wall and has to overcome gravity. That is the first differencebetween a glass wall cleaning robot and an ordinary walkingrobot on the ground. The mechanical structure for safe andreliable attachment to the vertical surface is needed. At themoment, four different principles of adhesion are used byclimbing robots: vacuum suckers, negative pressure,propellers and grasping grippers. Each one has advantagesand disadvantages at the same time.

2.2 Cleaning function

The motivation of developing this kind of robot is to clean theouter wall of high-rise buildings. The efficient cleaning is theultimate aim. The robot should have functions to move inboth the up-down direction as well as the right-left directionto get to every point on the glass. In order to finish thecleaning task, the robot has to face all obstacles and cross

them safely and quickly so that the cleaning movement would

Figure 1 Typical environments

Figure 2 Four kinds of glass curtain walls

A series of pneumatic glass-wall cleaning robots for high-rise buildings

Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong


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cover the whole areas. Even if it is very reliable, the cleaning

robot is still not a satisfactory product if it takes longer to

clean a certain area than human workers would. The robot

should find an efficient cleaning trajectory to carry out its

work. From this point of view, the efficient cleaning

equipment and quickly moving structure on the glass

surface are needed for the robotic system.

3. The overview of the family

There are three driving methods for walking robotic system.

The fluid drive is not suitable for climbing robots because of

the problems such as non-cleanliness and leakiness. The

family of our autonomous climbing robots for glass-wall

cleaning are totally actuated by pneumatic cylinders and

sucked to the glass wall with vacuum grippers (Figure 3). The

robots do not feature any electrical motors. The first two

prototypes are mainly used for research and the last one is a

real commercial product designed for cleaning the glass

surface of the Shanghai Science and Technology Museum.

The main specifications of the cleaning robotic systems are

summarized below:. highly dexterous and light mechanism;. high power-to-weight ratio for the driving system;. autonomous path planning and efficient cleaning;. water saving; as it reclaims, purifies and recycles the

sewage, the robot is a water-saving cleaning device;. enough intelligence for discriminating obstacles in a global

environment; and. easy remote control to provide global task commands or

emergency-type interaction.

With the pneumatic actuators the climbing robot can be made

lightweight which is one of the most important specifications

for devices working on high-rise buildings. Here, the

definition of “power-to-weight ratio” is given, which is the

ratio of the drive force Fdrive to the weight Gdrive of driver

construction. Compared with a motor-driven linear-motion

unit, a rodless cylinder with similar specifications is 1-2 times

lighter (Table I).Secondly, the motion driven by pneumatic actuators has a

passive compliance which makes the robot safer than driven

by motors under the situation of interacting with the brittle

glass. The practicable suction method on window glass is to

use vacuum suckers controlled by a vacuum ejector (Figure 4)

which needs to share the compressed air source with other

pneumatic cylinders.However, these benefits of the pneumatic system are offset

by adding the characteristic of nonlinearities and making

precise position control difficult to achieve. A closed-loop

control system utilizing a pneumatic pulse width modulation

(PWM) is employed to attempt to control solenoid valves. For

our robotic systems, different methods are used to realize the

precise position control, which will be introduced in Section 4.

3.1 Sky Cleaner 1

We designed Sky Cleaner 1 for cleaning the glass top of the

Beijing West Railway Station before 2000. This robot was

firstly named Washman. The system consists of a robot which

is remotely operated and autonomously moves on glass walls

to accomplish the cleaning action, and a support vehicle

stationed on the ground providing electricity, air source and

cleaning liquid for the robot. The supporting vehicle pumps

the water to the brushes for cleaning; the drainage will then be

collected and returned to a storage tank located in the front of

the supporting vehicle. Approximately, 90 percent of the

water can be re-collected using this system.

Table I The contrast between electrical and pneumatic actuators

Driven linear guidance units

Pneumatic Electrical

Items NORGREN SMC NEFF

Model 46140/400 MYC-400 WH50/400

Fdrive (Kg) 75.0 75.0 67.0

MX (NM) 39 19.6 16

MY (NM) 110 58.8 87

MZ (NM) 110 19.6 50

Weight for the unit (Kg) 4.9 8.9 6.16

Weight for actuators (Kg) ,1.0 ,1.0 6.0

Connector (Kg) 0.5 0.5 0.5

Total weight (Kg) 6.4 10.4 12.66

Power-to-weight ratio 11.72 7.21 5.29

Figure 3 Sky Cleaners

Figure 4 Vacuum ejector




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The lightweight robot can move on the surface of a slope up

to 458 in two perpendicular directions. The frame structure is

adopted in the robot to satisfy the requirement of movement

(Figure 5). The main body consists two cross-connected

cylinders named X and Y. Connected at the ends of the

X and Y cylinders are four short-stroke foot cylinders named

Z, whose function is to lift or lower the vacuum suckers in the

Z direction and support the body on the wall. Each group of

vacuum suckers lay as the line distribution. The robot needs

precise position control when it moves on the surface in order

not to touch any obstacles. Outside the Z cylinders there are

two brush cylinders connected to the ends of X cylinder. The

passive cleaning head is designed to be capable of supplying

the detergent and collecting the drainage. In this

construction, this robot moves and cleans simultaneously to

avoid a move-stop-clean sequence.Two kinds of external sensors are on the robot: infrared

sensors and ultrasonic analog sensors. They are responsible

for collecting information about the operational environment.

The first one is sensitive to frames and the other is used to

detect the windows seals (Figure 6).A PC is used as a console on the ground, and onboard

controller includes a PC104 and a programmable logic

controller (PLC). The PC104 is in charge of the global

intelligent control such as planning, identifying the sensors

inputs. The PLC is an assistant controller that collects the

internal switch sensor signals and actuates all the solenoid

valves.Figure 7 shows the process of crossing an obstacle when the

robot moves from one glass to another in the right-left side. In

this process, the brush-sets are all in up-state and no touch

with glasses:. The robot is in home state, and the sensor detects the

obstacle in the moving direction.. The robot approaches the seals and begins the position

control.. The vacuum suckers connected to the Y cylinder are

attached to the edge of one plank, the X cylinder moves

from right to left.. The vacuum suckers in the X direction are attached to the

two glass planks, the Y cylinder is moving from right to

left and the vacuum suckers connected to the Y cylinder

straddle the seal.. The vacuum suckers connected to the Y cylinder are

attached to the two glass planks, the X cylinder is moving

from right to left.. The robot is now in home state again, and the process of

crossing the obstacle is over.

Sky Cleaner 1 is the first prototype designed by our groups.

The system has only limited dexterity and cannot work on avertical wall. Because it has no waist joint, the robot is unableto correct the direction of motion. And the frequency fordealing with and crossing the obstacles is quite high so that

the cleaning efficiency is only about 37.5m2/h.

3.2 Sky Cleaner 2

The follow-up project was aimed at developing a cost-

effective, mobile and hassle-free robotic system for moving onvertical glass walls. Just to be on the safe side, a following unitis added to the system for protection. The function of this uniton the top of the building is simple and primary (Figure 8(b)).

There is a force sensor used to detect the tensile force of thefollowing cable. In this way, the weight and payload of therobot are no longer limited by the wall surface and the suckers

because the weight of the hoses from the supporting vehicle iscompletely supported by the following cable. Sky Cleaner 2 isdesigned to be compact and easy to transport from place toplace (Figure 8(c)). It is featured with 16 suction pads which

can carry a payload of approximately 45 kg including its bodyweight. Because of the special layout of the vacuum suckers,the robot can move in all directions freely without attention tothe seals.Two pneumatic cylinders provide both vertical and

horizontal motion. Located at the centre of the robot, aspecially designed waist joint gives a turning motion to the

robot (Figure 9). A relatively small degree of rotation (1.68)per step is turned in the present stage. Two pairs of simple

Figure 5 An artistic impression of Sky Cleaner 1

Figure 6 Sensorial outputs




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brake cylinders are added to the position-controlled cylinders.

A PWM method associates with a braking mechanism to

achieve better position accuracy for placing the suction pads

as close as possible to the window obstacles when a feedback

signal has been detected by the ultrasonic sensors.Only an onboard PLC executes a sequence of solenoid

valves on/off actions to perform commands that are sent by

the operator through the PC console. Sky Cleaner 2 is

portable and cleaning efficiency is about 75m2/h. But

considerable stress is laid on weight reduction, the

construction stiffness is somewhat low so that there is a

small distortion while cleaning and climbing.

3.3 Sky Cleaner 3

Based on the Sky Cleaners 1 and 2, Sky Cleaner 3 is a real

commercial product designed for cleaning the complicated

curve of the Shanghai Science and Technology Museum

(Figure 10). The building top is 40m from the ground. The

total surface area of the outer wall is 5,000m2. Owing to the

special arc shape, each glass is connected to its surrounding

glasses at a 28 angle.The major challenge in designing a robotic system is the

ability to overcome the horizontal angles on the surface and to

carry out the cleaning process automatically. At the same

time, since the cleaning device has to work on a sloped glass

surface, the pressure between the robotic mechanisms

supporting the attachment and the surface should be

sufficient to ensure stable interaction conditions on the

surface. On the other hand, the force should not become too

great, as this could crush the planks. As a conclusion, this

cleaning device should work autonomously and should be as

light as possible.Our group secured the commercial contract for this project

throught bidding. During the implementation of the project,

the building administrator of Shanghai Science and Techology

Museum gave us extensive support.The robotic system consists of three parts:

1 a following unit;2 a supporting vehicle; and3 the cleaning robot.

Figure 7 The process of crossing an obstacle

Figure 8 Sky Cleaner 2 system

Figure 9 A CAD design and a real photo of Sky Cleaner 2

Figure 10 The robotics system of Sky Cleaner 3




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A hose for water, a tube for pressurized air, cables for control

signals are provided from the supporting vehicle on theground.Sky Cleaner 3 has the similar structure to the former two

prototypes (Figure 11). A turning waist joint actuated by apendulumcylinder connects theXandYcylinders.Onoppositeends in the Y direction there are also four brush cylinders. Anadaptive cleaning head is designed especially for efficient

cleaning. When the glass is being cleaned, the water is notallowed to drip down; it is drawn off the glass wall through avacuum pump on the robot. Then the water flows down and iscollected on the supporting vehicle on the ground. At last the

drainage is filtered, and then reused for cleaning.Because the glass walls of the Shanghai Science and

Technology Museum have no window frames, there aresupporting wheels near the vacuum suckers in the X and Ydirections, which have been added to the mechanicalconstruction to increase the stiffness. A specially designed

ankle joint gives a passive turning motion to the suckers inorder to realize the movement from one column of glasses toanother in the right-left direction (Figure 12). All mechanicalparts are designed specifically and mainly manufactured in

aluminum to meet the requirements of the lightweight anddexterous movement mechanism.A PLC is used for the robot control system (Figure 13),

which can directly count the pulse signals from the encoderand directly drive the solenoid valves, relays and vacuumejectors. The communication interface between the PLC andthe controller of the following unit is designed to synchronizethe following movement of the cables.The robot is able to move autonomously on the glass to

tackle the local perceived situation. The controlling andmonitoring is achieved through the graphical user interface(GUI) to allow an effective and user friendly operation. Someimportant information including the global environmentalparameters and some important references for sensors will bepassed to the controller on board. All status information whileworking will be sent back and displayed on the GUI in thefeedback phase.A specific cleaning trajectory is essential for the cleaning

movement to cover all the unoccupied areas in theenvironment. Area-covering operation also named completecoverage path planning is a common and useful kind of pathplanning, which requires the robot path to cover every part ofthe workspace. For Sky Cleaner 3, if the robot cleans the worktarget in the right-left direction, it has to cross two-degree-angle edges several times. But it can work and cleanuninhibited in the vertical direction, because that way theglasses are considered as forming a plane. As a result, the robotbegins to clean the glass wall from the upper left point, andthen works its way down (Figure 14). It moves to anothercolumn when the first column of glasses is finished cleaning.Some areas at the top where some eaves are fastened and at thebottom near the ground cannot be cleaned for safety reasons.The coverage percentage on this small working area is over 93percent and the cleaning efficiency is 125m2/h (Figure 15).

4. Pneumatic control strategy as the coretechnology

The pneumatic systems in Sky Cleaners include X, Y and Zcylinders, brush cylinders and the vacuum suckers. The majorchallenge in pneumatic system is the ability of a controlsystem to deal with hysteresis which is caused by coulombfriction, temperature, and manufacturing tolerance stack up

Figure 13 Control system

Figure 11 Sky cleaner 3 prototype

Figure 12 The joint of the vacuum suckers




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of the valves. Usually, the proportional servo valves are used

to drive cylinders to realize the accurate position control. Now

a lot of researchers (Robert and Bone, 1997) have tried to use

on-off solenoid valves to realize this function of pneumatic

actuators due to its cheap costs. Among presented control

methods, the PWM has drawn most attentions for its

simplicity of hardware construction.

4.1 PWM method

The PWM which was developed for DC motor drives at first,

is to use the controller to create pulse signals to drive solenoid

valves of the pneumatic system (Qi and Surgenor, 2003). The

principle of typical PWM signal is shown in equation (1).

Where Ts is the PWM period; To is on time; t is the duty (the

percentage of on time to the PWM period) on the valve which

determines the output flow rate or pressure to the cylinder

chamber. The relationship between the duty of valve and its

output pressure is shown in Figure 16. The bigger the duty,

the bigger the output pressure:

t ¼ T o

Ts

£ 100 percent ð1Þ

4.2 Fuzzy PID for Sky Cleaner 1

Only one pair of high-speed on-off solenoid valves is used to

control the air pressure to the two chambers of the X and Y

cylinders on Sky Cleaner 1. An encoder and a set of gear and

rack are used to feedback the position of the piston of each

cylinder (Figure 17). Generally, the cylinder will move at full

speed with 100 percent high-speed on-off solenoid valve duty

on one side, 0 percent duty on the other side. When the

sensors detect window obstacles, usually duties on both sides

will change according to the feedback signals. Here, the

solenoid valves’ delay time to open and close is ignored. A

duty of 100 percent means the solenoid valve is fully open, a

duty of 0 percent means it is fully closed.

Figure 14 Cleaning trajectory

Figure 15 Sky Cleaner 3 is cleaning on the target glass wall

Figure 16 The principle of PWM

Figure 17 The scheme diagram of the X cylinder




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However, the benefit of this kind of simple valve is offset by

the limitation of the valve response and its discrete on-off

nature. For Sky Cleaner 1, fuzzy PID is used to realize the

precise position control of the X and Y cylinders to deal with

the nonlinearities. The results getting from the actual system

show that the fuzzy controller can fit into the robot’s running

in different conditions and achieve the designed goal.

Comparing with the normal PID controller, this fuzzy

controller has better capability (Figure 18).

4.3 Proportional control with mechanical brakes for Sky

Cleaner 2

In order to simplify the control strategy, two pairs of simple

brake cylinders are added to the position-controlled X and Y

cylinders on Sky Cleaner 2, respectively. Furthermore, a

PWM proportional control method is proposed. The duty is

calculated by equation (2). Where kp is proportional

coefficient, xd is desired position, x is current position.

When the cylinder arrives at the desired position, the brake

cylinders will mechanically stop it. This control method has

been tested practically on the X and Y cylinders (Figure 19):

t ¼

100 kpðxd 2 xÞ $ 100

kpðxd 2 xÞ 0 # kpðxd 2 xÞ # 100

0 kpðxd 2 xÞ # 0

8>><>>:

ð2Þ

4.4 Segment and variable bang-bang controller for

Sky Cleaner 3

The design of both the X and Y cylinders of Sky Cleaner 3, to

which the vacuum suckers are attached, is cheap, simple and

efficient, but the scheme of the X cylinder is even simpler

than that of the Y cylinder. Like Sky Cleaner 1, we only use a

pair of high speed on-off solenoid valves for driving the

X cylinder. However, the Y cylinder has to raise a load of

25 kg in order to push the cleaning brushes with a friction

force when the robot is cleaning downwards from the top of

the building. Moreover, the required cleaning efficiency of the

robot cannot be met because the high-speed on-off solenoid

valves cannot actuate the cylinder fast enough. In order to

accelerate the Y cylinder, a larger ordinary 3-position 5-port

solenoid valve (valve 5 in Figure 20) is used to bypass the

high-speed on-off solenoid valves. The main reason for this

simpler design is that Sky Cleaner 3 mainly moves and cleans

along the Y direction, while the movement frequency in the

X direction is very low (Figure 20).A method of segment and variable bang-bang controller is

proposed to implement the accurate control of the position

servo system for the X cylinder during the sideways

movement. Generally, the conventional bang-bang controller

(Zhang et al., 2004) for the pneumatic system is described

with equations (3) and (4). The control will be finished when

equation (4) is satisfied:

Ui ¼ 2UMAXðesÞ i ¼ 1; 2 ð3Þ

Figure 18 Control profiles of the X cylinder

Figure 19 30 mm-position profiles of the X and Y cylinders afterdetecting obstacles which are pointed out by red lines




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jesj # 1 ð4Þ

Where es is the position error, 1 is the limitation to the

position error, U1 and U2 are the control signals for the two

chambers of the X cylinder and UMAX is the maximum of the

control signals. Only the position error is used as the switch to

change the control without considering the factor of velocity.

However, the velocity of the piston is not zero even if the

piston is just at the ideal point. The movement will not be

finished and the control function will have to act for the

system because of the overshooting, which in the end will

cause oscillations. Based on this point, an improved variable

bang-bang controller is proposed described with the following

equations (5) and (6). Where ev is the velocity error, c is a

constant, sgn () is the signal function and y is the constructor

function synthesizing the position and velocity for movement

evaluation. Equation (6) shows that the control signals are

computed according to sgn (y).

y ¼ ev þ Ce2s sgnðesÞ ð5Þ

Ui ¼ 2UMAXsgnðyÞ ð6Þ

Furthermore, a segment strategy has been devoted to this

method in order to improve the stiffness and eliminate the

system nonlinearities. Here, two different control strategies

are needed. Firstly, when window obstacles are detected, the

robot should begin to control according to equations (5) and (6)

while the distance to obstacles is larger than eb. Where eb is

the limitation between the first step and the second step. In

the second, the absolute value of es is smaller than eb. The

initial pressure will be applied to the chambers during this

phase. The chamber which was open to the air is under initial

pressure. The goal of the measure is to increase the pressure

in the chambers when the piston is close to the desired

position.Figure 21 shows the profiles of position and velocity using

the method of segment and variable bang-bang controller.

The es and ev approach zero together. It is seen that the

movement is smooth (Table II) and the maximum of the

velocity is 680mm/s.

5. Conclusion

This paper describes a series of glass-wall cleaning robots

totally actuated by pneumatic cylinders. In contrast to

conventional theoretical research, this project finishes the

following innovative work:. Firstly, a summary on the basic functions for the glass-

wall cleaning robot is given. Three kinds of autonomous

climbing robots with sliding frames for glass-wall cleaning

are presented one by one. They are totally actuated by

pneumatic cylinders and attach to walls with vacuum

suckers. Based on the research background of Sky

Cleaners 1 and 2, Sky Cleaner 3 is a real commercial

product for cleaning the glass walls of the Shanghai

Science and Technology Museum.. The robots have to keep to and move on the glass of

arbitrary slopes while accomplishing the cleaning tasks.

They are portable, dexterous to adapt to the various

geometries of the wall, intelligent enough to

autonomously cross the obstacles. The specification

features of the Sky Cleaners are shown in Table III.. Pneumatic control strategy as the core technology is

discussed throughly. Three nonlinear control methods are

proposed for controlling three robots, respectively. The

advantages and the characteristics are analyzed in detail.

Testing results implie that the method can be realized and

meet present needs.

It is noted that the air source, cleaning liquid and control

signals of Sky Cleaners should be provided by the supporting

vehicle stationed on the ground. Even if the last prototype is

intelligent, the suitable working height is below 50m because

Figure 21 50 mm-movement position and velocity profiles of theimproved bang-bang controller

Figure 20 The scheme of X and Y cylinders




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the weight of the hoses has to be taken into account when the

robots work in mid-air.Now our research is focusing on the realization of new

passive suckers which will save considerable power. Because

of the unique vibrational adsorbing principle, the passive

suckers can attach not only to glass, but also to a wall with

aluminum tiles. In the future, these novel suckers will

hopefully be used on our new climbing robots to enable them

to move freely on vertical surfaces.

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pp. 756-62.Liu, S., Sheng, W., Xu, D. and Wang, Y. (2000), “Design of a

new wall cleaning robot with a small control system”, High

Technology Letters, Vol. 10 No. 9, pp. 89-91.Liu, R., Zong, G., Zhang, H. and Li, X. (2003), “A cleaning

robot for construction out-wall with complicated curve

surface”, Proceedings of CLAWAR 2003, Catania, Italy,

September, 2003, Vol. 2003, pp. 825-34.Longo, D. and Muscato, G. (2004), “A modular approach for

the design of the Alicia3 climbing robot for industrial

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G. and Chen, S. (2001), “Climbing service for duct

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reactor”, Proceedings of the 32nd International Symposium

on Robotics, Seoul, Korea, Vol. 19-21, pp. 41-5.Nishi, A. and Miyagi, H. (1993), “Wall-climbing robot using

propulsive force of a propeller (mechanism and control

system in a mild wind)”, JSME International Journal Series

C: Dynamics, Control, Robotics, Design and Manufacturing,

Vol. 36 No. 3, pp. 361-7.Qi, Y. and Surgenor, B. (2003), “Pulse-width modulation

control of a pneumatic positioning system”, Proceedings of

IMECE’03 2003 ASME International Mechanical

Engineering Congress & Exposition, Washington, DC, USA,

November, 1-10.Robert, B. and Bone, G.M. (1997), “Accurate position

control of a pneumatic actuator using on/off solenoid

Table III Specification features of the Sky Cleaner series

Type capability Sky Cleaner 1 Sky Cleaner 2 Sky Cleaner 3

Target character Glass wall 0-458 Glass wall 0-908 Glass wall 0-908 (with ,28 angle)

Efficiency (m2/h) 37.5 75 125

Cross obstacles (mm2):

height 3 width

Window frame: 30 £ 60 Window frame: 30 £ 60;

seal: 21 £ 20

Window frame: 10 £ 60;

seal: 21 £ 20

Weight (kg) 25 35 45

Body mass (mm3):

length 3 width 3 height 935 £ 900 £ 320 1,220 £ 1,340 £ 370 1,136 £ 736 £ 377

Supporting units The supporting vehicle The supporting vehicle and

the following unit

The supporting vehicle and

the following unit

Supply water (L/hour) 50 (reused) 50 (reused) 50 (reused)

Operators 1 1-2 1-2

Table II Experiment results of the improved bang-bang controller

No. 1 2 3 4 5 6 7 8 9 10

Condition Po ¼ 6.5 Mpa, C ¼ 5, eb ¼ 10 mm, Ts ¼ 35 ms, 1max ¼ ^0.5 mm, n ¼ 10

Desired position (mm) 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0

Actual position Si (mm) 50.0 50.1 49.8 50.2 49.8 50.5 49.7 49.9 49.9 50.0

Average(mm) �s ¼Pn

i¼1 si=n ¼ 49:99 ðmmÞ

s (mm) s ¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiPni¼1 ðsi 2 �sÞ2=ðn 2 1Þ

q¼ 0:23 ðmmÞ

Position accuracy (mm) Vr ¼ ^3s ¼ ^0:69ðmmÞ , ^1 ðmmÞ




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valves”, Proceedings of the 1997 IEEE International Conference

On Robotics and Automation, pp. 1196-201.Wang, W. and Zong, G. (2001), “Controlling and sensing

strategy for window cleaning robot”, Journal of Chinese

Hydraulics & Pneumatics, No. 1, pp. 4-7.Zhang, H., Zhang, J., Liu, R. and Zong, G. (2004), “A novel

approach to pneumatic position servo control of a glass wall

cleaning robot”, Proceedings of IROS 2004, Sendai, Japan,

September 28-October 2, pp. 467-72.

Further reading

Oyama, O. et al., (1997), “Reduction of ripple in a pneumaticregulator with a solenoid valve”, Journal of the JapanHydraulics & Pneumatics Society, Vol. 28 No. 6, pp. 673-8.

Corresponding author

Houxiang Zhang can be contacted at: [email protected]




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