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.
150
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
Industrial Robot: An International Journal
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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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
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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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
153
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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
154
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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
155
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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
156
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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
157
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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
158
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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J.C. (1998), “REST: a sixlegged climbing robot”, European
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(2002), “Innovative service robot systems for facade
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and Systems EPFL, Lausanne, Switzerland, October 2002,
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G. and Chen, S. (2001), “Climbing service for duct
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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
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
159
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]
A series of pneumatic glass-wall cleaning robots for high-rise buildings
Houxiang Zhang, Jianwei Zhang, Wei Wang, Rong Liu and Guanghua Zong
Industrial Robot: An International Journal
Volume 34 · Number 2 · 2007 · 150–160
160
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