ae 499 special topics_jared_cokley

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American Institute of Aeronautics and Astronautics

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Electrostatic Adhesion Device for Orbital Debris Removal

Jared M. Cokley1

Embry-Riddle Aeronautical University, Daytona Beach, FL, 32114

Currently there are five methods available which can be used to dock an object to another object of

interest. Chemical adhesion, space applicable suction cups, synthetic cups, mechanical grippers, and

electrostatic adhesion. For the applications related to aerospace engineering, electrostatic adhesion was

chosen as the preferred choice. Electrostatic adhesion involves utilizing high voltage circuit pads, to generate

adhesive force along the pad’s surface area. By assimilating a macro-fiber composite (MFC) as an actuator,

designed copper circuit, Kapton tape, and a strain gage a practical model of adhesive gripping is created.

Simulating the device in a zero gravity SimMechanics environment allows the device's behavior to be

observed.

Nomenclature

A = electrode area of EAD device

C = capacitance

d = normal distance between EAD and object of interest

EAD = electrostatic adhesive device

ERAU = Embry-Riddle Aeronautical University

e = permittivity of material between electrodes

GF = gage factor of strain gage

MFC = macro-fiber composite

N = normal force

R = resistance

µk = coefficient of kinetic friction µs = coefficient of static friction

V = voltage source

W = energy stored in capacitor

Xe = electric susceptibility of the dielectric

I. Introduction

The ultimate goal of the electrostatic adhesion device is to be able to adhere to any surface with feedback from

attached sensors. In order to design and implement this technology a series of milestones demonstrating the

progression of the pads must be established. Static adhesion is similar to the effect caused by rubbing a balloon

against hair. Once the balloon is pulled away from the hair, electrical forces provide small adhesive forces in the

medium between the two objects.

Implementing electrostatic adhesion requires the use of more than one electrostatic adhesive device (EAD) due

to the current technology available. In order to use this type of gripping mechanism, the design, fabrication, and

testing of one device will be researched and applied to a zero gravity environment. Observing the actuation

capabilities of piezo ceramic devices and their compliance with high voltage pads will validate its practical

capabilities. Figures 1 and 2 show the concept of operations for docking using four smaller nanosatellites equipped

with their own EAD.

1 Student, Aerospace Engineering, 800 S. Clyde Morris Blvd Daytona Beach, FL, AIAA Member Grade: N/A

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Figure 1: Concept of Operations for Orbital Debris Removal.

Figure 2: Rocket Body w/ 4 Nanosatellites Attached

II. EAD Design and Fabrication

A. Overview To develop an EAD requires laboratory facilities which allow the circuit design to be printed on copper sheets, a

chemical etching station, high voltage battery supply, and an electrical wiring and strain gage installation station.

B. Equations Observed

F = µk N (1)

F = µs N (2)

C = eA/d (3)

e = (ΔR / R) / GF (4)

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C. In-Lab EAD Testing

In ERAU's Spacecraft Development Lab, EAD copper circuits were printed to determine the best type of design

for adhesive purposes. various designs were created in SolidWorks. Figure 3 shows the results of wax printing on

copper sheets.

Figure 3: Wax Circuit Design Printed on Copper Sheets.

In the Material's Lab, the unnecessary copper not apart of the actual circuit design was etched away using ferric chloride. After removing the wax layer on the pad, the desired copper circuit was revealed (shown in Figure 4).

Figure 4: Etched Spiral Design.

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Figures 5 and 6 show the result of shear force for the spiral design on different material types. The variation

between the two materials show an EAD will behave differently depending on whether the surface is conductive or

an insulator. In these trials, after observing a trained personnel follow strict safety guidelines with operating a 3,000

V powered EAD the highest adhesive force was 11 N.

Figure 5: Shear Force for Spiral EAD on Aluminum.

Figure 6: Shear Force for Spiral EAD on Glass.

D. MFC Implementation

Macro-fiber composites (MFC) are flexible, durable, and reliable piezo ceramic actuators originally developed at

the NASA Langley Research Center in 1996. Using an MFC with the EAD design provides increased strain actuators

efficiencies and conforms to the object of interest’s surface. Figures 7-12 show the application of an MFC and a strain gage. During testing, the maximum deflection of the MFC was near 15°.

Figure 7: Non-Actuated EAD Layout.

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Figure 8: Actuated EAD Layout.

Figure 9: MFC with Back of EAD.

Figure 10: MFC Integrated on Back EAD.

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E. Strain Gage Testing

Figure 11: MFC Attached to EAD in Cantilever Beam Assembly.

Figure 12: Digital Multimeter Used to Measure Strain.

Table 1: EAD Strain Gage Values from Test

Test # GFR_o

(Ω)

R_ave

(Ω)

Delta_R

(Ω)

Applied

Voltage (V)

frequency

(Hz)

Strain

(%)1 2 351.17 351.800 0.630 0-5 square 2 0.090

2 2 351.19 351.120 0.070 0-2.5 square 2 0.010

3 2 352.15 352.165 0.015 2.5-5 square 2 0.002

4 2 352.15 351.798 0.352 0-5 square 4 0.050

5 2 351.19 351.115 0.075 0-2.5 square 4 0.011

6 2 352.16 352.150 0.010 2.5-5 square 4 0.001

7 2 351.45 351.877 0.427 0-5 sine 2 0.061

8 2 351.17 351.075 0.095 0-2.5 sine 2 0.014

9 2 351.53 352.190 0.660 2.5-5 sine 2 0.094

10 2 351.53 351.958 0.428 0-5 sine 4 0.061

11 2 351.18 351.085 0.095 0-2.5 sine 4 0.014

12 2 351.19 352.157 0.967 2.5-5 sine 4 0.138

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III. Developing EAD in a Zero-G Environment

To simulate the EAD's behavior in a zero gravity environment MATLAB's SimMechanics was used. The main

research focus within MATLAB was simulating the adhesive or frictional effects between the pads and the object

of interest.

F. SimMechanics Familiarization

A double pendulum along a linear rail was modeled to become familiar with the SimMechanics interface. In the

figure below the green block travels at a constant velocity in a zero gravity environment. In this experimental

environment, the pendulum doesn't oscillate due to gravitational acceleration equaling zero and the actuated block

moving in a constant velocity.

Figure 13: Constant Velocity Double Pendulum in Zero-G.

Collision effects within SimMechanics were studied to determine viable applications for final simulation. The

bouncing ball example provides a quick review of the behavior of a bouncing ball on Earth. In this model,

gravitation of 9.81 m/s2 was used. By imposing a penalty force within Simulink to counteract the gravitational force

of a falling ball, the ball's velocity attenuates after contact with the ground plane. The penalty force ultimately

reduced the ball's velocity to zero.

Figure 14: Bouncing Ball with Penalty (Impact) Force.

The same ball was used to study the ball's rolling motion. Modeling a rolling ball along a flat surface shows the

behavior of contact forces which is similar to the penalty force observed above within SimMechanics. In the rolling

ball example, the penalty force doesn't produce enough force to propel the ball away from the simulated ground.

Instead it balances the force between the ball's normal force, as it allows only translational motion along the xy-plane

which rotates the ball along the plane.

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G. SimMechanics’s Friction Tools

The first generation of SimMechanics features a small library dedicated to static and kinetic friction. Appropriately

using these blocks permits the ideal simulation of basic frictional force behavior.

H. Velocity Damping from Frictional Effects

Static friction was the best environment to model the behavior of the EAD during adhesive manipulation. This

environment consist of three blocks with the top two blocks generated to have both static and kinetic friction characteristics. The bottom block is considered the actuated block which transfers its momentum to a frictional

block once planar contact is made. A series of experimental tests were conducted to observe the limitations and

capabilities of these frictional blocks.

Initially all three blocks were aligned in the same yz-plane. A sinusoidal input signal was fed to the actuated base

block. The base block was provided an initial position, velocity, and acceleration signal. By varying the signal initial

conditions different block separation positions, velocities, and friction reactions were observed. Offsetting the

location of the base block along the x-axis produced a model which permitted the contact forces to be observed after

only after the time when the blocks become in contact. This trial validated the only acting force on the blocks to be

the result of friction. Eliminating acceleration from the base block removed the possibility to actuate the friction

blocks since an anomaly occurred which applied a velocity to all three blocks instead of only the base block.

Reducing the simulated environment into a two dimensional virtual world provided pure analysis of the

kinematics of the system. frictional effects. Table 2: Initial Conditions Used in SimMechanic Models

Initial Condition Units

µs 0.1

µk 1.65

gE 9.81 m/s2

g 0 m/s2

Figure 15: Initial Offset Frictional Blocks. Figure 16: Elapsed Offset Frictional Blocks.

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Figure 17: Offset Frictional Blocks Under Gravity Velocity (Purple) and Position (Yellow) Graph.

I. EAD Friction

Figure 18: Initial Double Pendulum with EAD. Figure 19: Elapesed Double Pendulum with EAD.

Combining everything learned from the double pendulum, bouncing ball, rolling ball, and frictional block

models created the model seen in Figures 18 and 19. Inputting the same signal used in the frictional block model

to the blue base block created a simulation of the EAD in action when equipped with a manipulator. Replacing

the three sinusoidal inputs for position, velocity, and acceleration with one sinusoidal input modified by a general transfer function block to provide a filtered derivative created a more accurate simulation.

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Figure 20: Double Pendulum with EAD Adhered to Frictional Block Velocity (Purple) and Position (Yellow)

Graph.

IV. Conclusion

By specifying the known adhesive force produced by the EAD, reverse kinematics can be used to determine the

motion required from the EAD's manipulator. This entire intensive process of designing and simulating an electrostatic

adhesive highligted a few areas of concerns. Providing high voltage levels near 3,000 V to only the EAD in the vacuum

of space will be a challenge. While researching the capabilities of SimMechanics modeling of an EAD, there were

instances where a simulation might not provide actual behavior of the docking method. These issues occur when the

EAD's velocity needs to be simulated to become a constant and linear value. Currently the ability to operate a double

pendulum within SimMechanics is based off a sinusoidal signal. If an object of interest is attached to the base of the

pendulum then an acceleration needs to be provided to the entire mechanism otherwise SimMechanics sets the entire system to travel at the constant velocity and not only the actuated block.

Overall this technology is possible, and its continued development will create an innovative way to dock to objects

of interest and can be applied to objects on Earth.

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Appendix

Figure 21: Frictional Blocks Simulink Schematic.

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Figure 22: Double Pendulum with Constant Velocity in Zero-Gravity.

Figure 23: Double Pendulum with EAD Adhered to Frictional Block Simulink Schematic.

Figure 22: Frictional Block Simulink Schematic

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Acknowledgments

I wouild like to acknowledge Dr. Bogdan Udrea for providing educational and motivational guidance throughout

my time at Embry-Riddle, Walter Saravia for primary assistance in testing the technology, and Dr. Kim for assistance

with MFC devices.

References

Saravia, W., Design, Fabrication, and Testing of a Proprioceptive Electroadhesion Pad for Space Applications, Daytona Beach,

Florida: Embry-Riddle Aeronautical University, 2015.

ae 499 special topics_jared_cokley

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