A Cost Effective and Light Weight Unipolar Electroadhesion Pad Technology for Adhesion Mechanism of Wall Climbing Robot

Electroadhesion technique being employed in variety of fields of science and technology is considered as a clamping technique for wall climbing robots. The focus of this research is to present a cost effective and light weight unipolar electroadhesion pad technology for wall climbing robots (WCR) capable of lifting a reasonable weight vertically. The literature demonstrates that most of the research related electroadhesion has been performed on bipolar electrode pads. The research presented in this paper indicates that unipolar electroadhesion pad showed favourable attachment on melamine and wood substrates giving encouragement for the realisation of unipolar WCR. Design considerations along with the attachment of anti-peeling tail are also considered for the realization of WCR. The controlling mechanism for unipolar wall climbing robot was not complex. In conculsion, unipolar electroadhesion pad of copper and aluminium is a feasible technique to develop a cost effective and light weight unipolar wall climbing robot. Keywords—Unipolar electrostatic adhesion, Wall Climbing Robot (WCR), Electrostatic Adhesion (ESA), electrostatic force, unipolar electroadhesive robot technology, unipolar Wall Climbing Robot.


I. INTRODUCTION
ALL climbing robots (WCR) are capable to adhere vertical walls and able to move vertically and horizontally with payload carrying capacity to perform various tasks.As in severe environmental conditions for human being, robots are means for observations and operations [1].These are widely used for maintenance, inspection and surveillance works in places where there human access is difficult or very dangerous due to unfriendly environment of social infrastructures.These infrastructures such as buildings, bridges, nuclear power plants, oil reservoirs, marine structures, and space ships, which play very much important roles in our daily lives [2], [3].To perform various tasks a WCR should be capable of high payload carrying capacity.The substitution of WCR to mitigate human beings, from performing variety of high-risk applications, has much attracted the attention of researchers over the past few decades [2].
Although the electrostatic adhesion technology was known to the researchers since decades but it was first used extensively in industries as electrostatic chucks for lithographic processes and silicon wafer-semiconductors [15], [17].Another industrial application of electroadhesion is for handling fibrous materials [18][19][20].Noticing the strong adhesion force of these electrostatic chucks researchers introduced this adhesion technology as a clamping pad for the wall climbing robots in recent years [16].Since then different kinds of wall climbing robots have been made along with detailed simulation and theoretical modelling study on bipolar electroadhesion pads [2], [21][22].However, there is a little study on unipolar electroadhesion pad for WCR.Geometries and the gaps between the electrodes make the fabrication of the robot difficult.However, the effect of unipolar electroadhesive pad for wall climbing robot is unknown.Previous research in this area has been very limited and very little work regarding the unipolar electroadhesion pad for wall climbing robot has been published.This paper is proposing a new cost effective and light weight unipolar electroadhesion pad for WCR.

II. DEPLOYMENT METHOD OF PROPOSED UNIPOLAR PAD ELECROADHESION TECHNOLOGY
Electroadhesion is an electrically controllable adhesion technology [23].Electrostatic field is the basic principal of ESA (Electrostatic Adhesion).Electrostatic field can provide an attraction force, called electroadhesion [24].However, the electroadhesion force is usually somewhat lower than the similar magnetic force.Therefore, the considerable force still can be produced with a suitable parameters selection of the electroadhesion pad.

W
To begin with the experimentation process the starting positive voltages are + 1000 volts, + 2000 volts, + 3000 volts, + 4000 volts, + 6000 volts, + 7000 volts, + 8000 volts.The deviation of electroadhesion force in kilograms associated with the mentioned factors will be discussed.A simple series of experiment is applied to produce electroadhesion force with respect to voltage plot.First the electroadhesive pad is gently laid on the substrate surface without weight.The electroadhesion pad was then energized with unipolar high voltage provided by self-made AC-HV-DC converter (voltage multiplier).First, all the four pads of different areas were charged with 1 kilo volts and then weight is applied to the pad until it detaches from the surface attached with due to electroadhesion force.The weight or force just before the detachment of the pad is recorded as maximum adhesion force.This test sequence is then for 1 kV, 3 kV, 4 kV , 6 kV ,7 kV and 8 kv and readings were noted shown in Figure 10, 11, 12 and 13.

Lateral Force of the Unipolar Pad
The unipolar electroadhesion pad showed rapid response when +ve HV dc is supplied to it.The unipolar electroadhesion pads showed attachment to the test surfaces within seconds when voltage applied.Weights were applied with gradual increment to overcome the electroadhesion force to the substrates (wall).The maximum forces measured before the unipolar electroadhesion pad gets slipped were considered the main practical unipolar electroadhesion force for wall climbing robots.A hissing sound was also noticeable during the voltage supply to the unipolar pad.The measured experimental results are shown in TABLE II.
From Figure 9, it can be clearly observed that the electroadhesion force, by unipolar pad, increases with the advancement in voltage.The force vs voltage relation is to some extent quadric parabola.Hence, it is possible to increase voltage in order to get high adhesion force.This research voltage limitation is 8 kV.However, increasing the HV supply should be in a limit so that the dielectric breakdown of the dielectric layer may be controlled otherwise leads to the failure of whole unipolar electroadhesion pad.The results depict that the high voltage range from 3 kV to 8 kV produces reasonable unipolar electroadhesion force.

VI. VALIDATION OF RESULTS
This proposed model has been validated experimentally.Figure shows that the valuable unipolar electroadhesion force (lateral force) is experimentally achieved for the development of unipolar electroadhesion WCR.The experimentation results recommend that for larger payload WCR larger unipolar pad area should be considered.

A. Comparison with Experimental Data
The theoretical model values were compared with experimental data.The theoraticall and experimental unipolar electroadhesion force is shown graphically in Figure 10, 11, 12, and 13 which indicates that the proposed model agreement is found to be good.In order to check the validity of the model voltage was changed at six different values in kilo Volts i.e. 1 kV, 3 kV, 4 kV, 6 kV, 7 kV and 8 kV and four unipolar electroadhesion pads were also taken into consideration with different areas.With all these parameters the the result of modal versus experiments were quite acceptable.The acceptable differences in the results may be due to ideal conditions which are difficult to achieve which will be fcused to minimized in future research.However, when the unipolar electroadhesion pads were operated on different non conductive walls with varying permittivity materials of substrate, it showed that walls with high permittivity produces more electroadhesion force than less permittivity.So further investigation of this subject will be carried out in future research in details. Figure 15 shows the forces acting on the WCR.In order to climb for the robot to the wall, the two components lateral force and peeling force must be countered.Lateral force (holding force) can be countered by providing sufficient frictional coefficient between the robot and the wall.Peeling force can be countered by shifting the centre of gravity (CG) towards the wall.However, CG cannot be completely shifted towards the wall.To avoid peeling, anti-peeling supports were used such as tail supports.
There are two wheels, namely, rear wheel and front wheel.The two wheels are attached using the unipolar electroadhesion pad as belt drive, which is the mechanism for the locomotion of the robot.The high voltage power is applied to the unipolar pad, when the robot is in motion.An arrangement is made for this purpose.A wooden shaft is fixed to the skeleton and a ball bearing is attached on the shaft such a way that the ball bearing is always in contact with the belt.Ball bearing rolls as the unipolar electroadhesion pad moves, as both are in contact.The friction between them is less.The applied high voltage on ball bearing gets applied to adhesive pad (by ball bearing arrangement).The unipolar electroadhesion pad and the motors are attached mechanically but are operated separately as given in Figure 16.From the proposed schematic of unipolar electroadhesion WCR in Figure 14 and Figure 15, M is motors, B is ball bearing, W is wheel driver, T is tail and F is wood frame for WCR.A cost effective and light weight unipolar electroadhesion pad technology on wall climbing robot was presented in this paper.The unipolar electroadhesion pad has produced favourable amount of electrostatic adhesion force on vertical substrate.It shows working on non conductive substrates such as melamine wall and glass wall.This success of reasonable unipolar electroadhesion force creation is the encouragement for the unipolar electroadhesion wall climbing robot.Model skeleton for fabrication of WCR is also discussed with design considerations along with tail for anti peeling force.As a whole the complete control approach is not that much complicated and contains only a separate power supply to the unipolar electroadhesion pad.In short, the unipolar electroadhesion technology is feasible technique to make a cost effective , light weight and multiple surface robot capable of adhering to vertical walls making it wall climbing robot.

Figure 8
(a), (b) Potential unipolar electroadhesion pads for WCR, (c) the unipolar electroadhesion pad which can be utilized on Wall Climbing Robot B. Wall Climbing Robot Design Figure 8(c) is the basic skeleton of unipolar electroadhesion robot.It consists of two parallel plates of wood, since it is light in weight and non-conductor.The motors are attached to these plates.Top view and Side view of unipolar electroadhesion robot is shown in Figure 14 and 15, respectively.The unipolar electroadhesion pad wrap around the drive wheel and in contact with the ball bearing.The ball bearing moves as the unipolar electroadhesion pad moves with the wheel drive.

Figure 9
Figure 9 Experimental results of lateral force for unipolar electroadhesion pad of copper on melamine/wood wall surface: (a) P 8cm x 8cm (b) 12cm x 12 cm (c) 15 cm x 15 cm (d) 20 cm x 20 cm.The dotted regions are the lateral force regions which are practicable for Wall Climbing Robot