Proceedings of the Multi-Disciplinary Senior Design Conferencepage 1

Multi-Disciplinary Senior Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York 14623

Project Number: P11566

DESIGN AND ANALYSIS OF LOW COST SOLID STATE, EDDY CURRENT VIBRATION DAMPER

Tiffany Heyd Benjamin Hensel Mechanical Engineering Mechanical Engineering Rochester Institute of Technology Rochester Institute of Technology Jacob Norris Thomas Sciotto Mechanical Engineering Industrial and Systems Engineering Rochester Institute of Technology Rochester Institute of Technology

ABSTRACT [Abstract] ITT approached the RIT Senior Design program with NOMENCLATURE the need for a damper whose behavior can adequately be modeled by a finite element analysis software Explanation of equations used package, like Comsol. Key deliverables to a successful project would include a functional prototype Explanation of zeta calculations developed with space applications in mind that when tested would match the predicted performance from a Flexure model of the system. The prototype was to be delivered with appropriate test apparatuses and Stick slip documentation to allow in future development.

Whiskers It was hoped that after the completion of this project there would be a greater understanding of the effects Stewart Platform that go into designing, fabricating and modeling the PROJECT BACKGROUND & CUSTOMER behavior of an eddy current damping system. From the NEEDS onset it was apparent trade-offs would need to be ITT developed a solid-state eddy current vibration made between the customer’s needs and actual design damping system for space applications several years specs due to budgeting and scheduling constraints. ago. They developed a prototype that exceeded their The budget was $2000 and there were only about 25 analytical model by a factor of two and were unsure of weeks to complete the design, construction and testing why their model did not match the calculations made of the project. ITT spent five years developing theirs by finite element analysis. and, probably, more than $2000. It was assumed materials analogous to space appropriate materials The damping system is meant to mount as one of six could be used for fabrication due to the budget trusses on a Stewart platform that mounts between the constraint. A decision was made that it was more bus and payload on a satellite in low earth orbit. The important to develop a prototype that matches the positioning system of the satellite is constantly moving analytical model than a prototype that strictly follows to new orientations is order for satellite images to be the Looking at how ITT went about their design was taken. This induced vibration needs to be damped out useful in developing design concepts for our team. ITT before the sensitive instrumentation on the payload fixed an array of strong magnets and using a “flexure”, can take the images required. allowed a six finned copper vein to oscillate between

Copyright © 2011 Rochester Institute of Technology Proceedings of the Multi-Disciplinary Senior Design Conference Page 2 the gaps in the magnet array as shown in Figure 1. The magnet array is visible in Figure 2 and it becomes apparent that a motion control system is necessary to control rotation about the center of conductive vein (shown in Figure 3).

Figure 3: Motion control “flexure” on fully assembled damper (Photo courtesy ITT)

Functionally speaking, the damper would require between ½” and 1” range of motion (1.27cm to 2.54cm) at 1 Hz of vibration with spikes of 1 inch Figure 1: Conductive copper vein inserted in amplitude at 5 Hz. This was considered an extreme magnet array (Photo courtesy ITT). case scenario and it was to be assumed that the steady state vibration that needed to be damped would be 100 Hz at .005” of amplitude (127 µm). The resonant frequency of the total system could be assumed to be between 5-20 Hz. Another critical design constraint is seeing a damping constant (zeta) of between 10-25%. This was expressed as an optimal resistance measure to allow vibrations to be damped out quickly, but without threatening the wellbeing of any other parts of the system.

Because this system will be mounted on a satellite in space the system needs to be robust enough to function, without failure, for 10 years and because of this extreme environment everything would require a Figure 2: Magnet array (Photo courtesy ITT) factor of safety of two. Also, due to the strength of the magnets in use, it was also expressed that magnetic In discussions with ITT there were certain needs shielding would be required to protect any sensitive expressed that would need to be addressed in order to instrumentation from the potential effects of the strong call this project successful. Chief among them was magnetic field. delivery of a functional prototype, the performance of which could accurately be reflected with a computer model. In order to avoid the hassle of modeling “stick slip,” there should be no rubbing of moving parts in the prototype. Also discussed was the need for the prototype to be designed to parameters appropriate for delivery and use is outer space. It would need to be less than 1 kg (2.2 lbs.) and be able to operate in temperatures from -40°C to 80°C (-40°F to 176°F). Operation needs to occur in a vacuum and because of this no tin, zinc or organic volatiles can be used due to formation of “whiskers” and potential damage from off gassing. The damping system will be one of six struts in a Stewart platform that will need to dampen the vibration of a payload of 60 kg (132 lbs.). Currently the system mounts between the bus and payload using a ball joint system, which it is not within our scope to redesign.

Project P11566 Proceedings of the Multi-Disciplinary Senior Design Conference Page 3

DESIGN METHODOLOGY The first concept involved a rod shaped strong magnet To meet the needs of the customer, a series of moving through a coiled conductor that was help fixed engineering specifications were devised, that is met in place by a protective shroud. The coiling effect was would guarantee success in certain aspects of the explored because of the amplifying effect of the project. These include: solenoid on eddy currents. Figure 4 below illustrates the concept simply, pointing out the magnet (in green) 1. Operating temperature: -40°C-80°C moving freely between the copper solenoid (orange 2. Operating pressure envelope: 0 Pa spiral) and constrained at the ends by some method 3. Weight of system: <1kg (preferably a flexure for all systems). 4. Damping coefficient zeta:10-25% 5. Lifecycle: 158,000 cycles 6. Magnetic Shielding: 20 mG (at 6”) 7. Clearance of flexure movement: +/- .25-.5” 8. Factor of safety: 2 9. Load to damp: 10 kg 10. Frequency of maneuver: 1 Hz 11. Frequency of stationary: 100 Hz

Several options were investigated on how to damp vibrations induced in this situation. Understanding the nature of the vibration and the environment it is operating in are critical to making a choice between different damping options. Because the information Figure 4: Concept based on magnet moving about the nature of the vibration could be assumed to through fixed solenoid be one of a few standard cases and the environment of extraterrestrial space was defined by the customer, it The second concept explored again involved a rod was not necessary to design for multiple environments shaped magnet moving freely within a conductor, but and situations. this time the conductor was a tube. Again the system would be incased in a protective shroud and motion The methods explored of mitigating the disturbance would be constrained. This concept is illustrated included eddy current damping, hydraulic damping, below in Figure 5, with the conductor in orange and friction damping, elastic damping and fluid damping. magnet in green. Because of the harsh temperature fluctuations of space, most fluid and hydraulic damping systems would be rendered useless by boiling off their liquids. The friction system violated the “no stick slip rule” and the elastomer concept seemed to be difficult to make function in an environment that would damage most natural rubbers. The eddy current system seemed to be the best concept to explore.

The remaining considerations to explore would be both protecting the system from the environment it was operating in (making sure no foreign matter ended Figure 5: Concept based on magnet moving up in critical moving parts) and ensuring that the through solid conductive tube. damping system didn’t have any deleterious effects on the function of the satellite payload or bus. The third concept explored had a fixed array of magnets that had a conductor moving between them. From this three concepts were explored in an attempt Again, there is a shroud surrounding the system to to design the optimal system that could be delivered to protect it and has a motion control system keeping it the customer in a short time frame. together.

Due to the intricate design, as well as the thin characteristics of the stainless steel pieces, the flexure was cut via plasma laser. The company (insert company name here) assisted the group with the skill and equipment.

Iron Magnetic Fixture - (28 hours) The iron magnetic fixtures are cast gray iron. Although the fabrication was messy, the magnetic properties are utilized in the system. The iron first had to be milled to size and have parallel sides. After assuring this, each piece was cut to size We ended up choosing the third concept by weighing and milled for accurate size and angles. The sockets the strengths and weaknesses associated with for the magnet were milled to size assuring that the modeling, fabricating, potential damping effect and back of the socket was flat in order to take advantage weight of, concept development, amounts of magnetic of a closed magnetic circuit in the system. After the leakage of and potential customer satisfaction of each magnet sockets were milled out, a threaded hole was system. Reasons why the third concept seemed most placed in the back of the iron magnetic fixture in order appropriate included its low potential level of to secure it to the side of the wall of the aluminum magnetic leakage, similarity to the initial prototype the casing. The thread chosen was a #6-32 thread size. customer made and the potential to make this into the lightest system. Copper Conductor - (7 hours) As this is a sub assembly of the total assembly there were multiple pieces fabricated. The Feasibility analysis/ drawings four conductor pieces were cut to a 7” size. The, 5/16” diameter with 24 threads per inch, threaded rod Risk analysis was ordered and left in an ‘as is’ state. The last part of the copper conductor sub assembly is the copper fixture. These are four pieces, to be evenly spaced on the threaded rod, were milled to attain the high Fabrication accuracy and parallelism that is needed for this specific part. The center was threaded for a 5/16”-24 Fabrication (insert pictures perhaps?) thread The copper assembly makes use of the Casing - (10 hours) threaded rods and JB Weld. Once the four copper Step one was to machine the casing. The fixtures were threaded and spaced 2” apart on the rod, casing, as decided for ease of assembly, disassembly, JB Weld was applied to the copper in order to fix the and testing was to be broken into layers. Thus three copper conductor to the copper fixtures. This was 2” casing layers, one 1.5” casing layer, and 3 .5” done over a course of four days and applied to the four casing layers were called for. Two of the three .5” conductor plates. casing layers are used for clamping the flexure which will be discussed in the assembly section. The other Assembly - (7 hours) layers were used for spacing and supporting the First, the casing was assembled. The angle magnets and iron fixtures. corners were attached to the stacked aluminum tubing From the design, the casing was decided to layers by #6-32 screws and nuts. Not all holes aligned be a 4” by 4” Aluminum tube. This was ordered, cut between the corner angles and the tubing layers, so into layers, and then milled to assure accuracy. After each layer is individually altered to assure the tubing the layers were cut to size, thru-holes were placed in holes match with the corner angle holes. For assembly order to fix the iron fixtures as well as the angle and reassembly purposes, each layer and corner need corners to the sides. to match the original setup. The angle corners were fabricated similarly The magnets were then inserted into the as the layers. These four parts were used to strengthen magnet sockets of the iron magnet fixtures. Due to the the casing layers as well as assemble the layers into magnetic properties of the cast gray iron, the magnets one square tube. The aluminum corners were cut into placed in with relative ease. Magnets are also placed four 9” pieces then milled to assure accuracy. After in alternating order. Opposite poles are facing inward, being cut, thru-holes were placed in the sides in order towards the iron, in each of the iron magnetic fixtures. to line up with the respective thru-holes in the layers. With the casing assembled and the magnets in their fixtures, the next step was to place the iron Flexure - (x hours) magnetic fixtures into the casing. First layer placed in

Project P11566 Proceedings of the Multi-Disciplinary Senior Design Conference Page 5 was the middle one. After the first two were placed [How well did we meet customer needs, ways we opposite each other, the last two of the middle layer could have fulfilled them through substitution of were placed utilizing .25” thick shims. The two materials (use model to justify), and recommendations outside layers were assembled in a similar manner. to future groups] The iron magnetic fixtures were fixed to the aluminum casing by #6-32 screws. REFERENCES The copper assembly was slid into place [refereces in order of appearance] between magnets. A lock-nut was placed on each end of the threaded rod to where the flexures would touch and stop when slid into place. The two end aluminum ACKNOWLEDGMENTS layers were screwed in to clamp down on the flexures. The flexures were finally secured with an additional Our work could not have been completed without the lock-nut at each end, tightly screwed against the assistance of the following people: Dr. Alan R for his flexures. service as our guide and mentor. His seemingly infinite wisdom allowed us to do so much more than Changes to design while fabricating (put in we could have ourselves. Thanks to Mr. Phil Vallone this section?) of ITT in Rochester, NY, for representing his Epoxy vs. solder company and their resource contributions to the No epoxy to the magnets successful completion of this project. Thanks to Rob Larger threaded rod Kraynik of the RIT machine shop for his assistance, guidance and patience in the fabrication of our system. Thanks to Dr. Marca Lam and Dr. Linda Barton for Testing plan their individual roles in assisting with the testing of our system. We would also like to recognize the Modeling plan faculty and students who attended our design reviews, including Dr. Mark Kempski and Dr. P. RESULTS AND DISCUSSION Venkataraman, for their crucial feedback and criticism during the formative stage in the design process. [Results of tests and discussion of similarities to Special thanks also go to Mark Smith and the rest of model. Attempt to explain modeling difference] the staff in the RIT senior design center; the facilities CONCLUSIONS AND RECOMMENDATIONS were a great place to work and the staff was accommodating. engineering specifications.