Magnetic Vibration Damper for Space Applications

PlanningConcept Develop

mentDesign Fabricati

on

Test & Verificati

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Background Principle: When a conductor moves through a magnetic field, an eddy current is generated (like a paddle through water) which dissipates mechanical energy as electrical current through the conductor. The motion of the damper will behave according to the equation of motion for a spring-damper system, shown below. The zeta calculation referenced in customer needs backs out of the ‘c’ damping coefficient.

Concept Generation: • Magnets fixed, conductor mobile• Conductor fixed, magnets mobile

Design Selection: The first method was chosen to minimize magnetic leakage. The magnet array is mounted on a cast iron bridge to amplify the magnetic field strength and allows a copper vane to move between to dissipate the energy in the system. The motion is constrained by a set of laser cut flexures. The design sought to maximize use of off the shelf parts.

The magnets used are rare earth, neodymium magnets, rated at 14,800 Gauss with a pull force of ~40 lbs. Very strong.

Mission: To develop a prototype of a solid state eddy current damper for use in satellite and aerospace applications and to deliver it with an accurate analytical model of system performance and test fixture in 25 weeks.

Team (left to right):Jake Norris (ME)- Fabrication EngineerTom Sciotto (IE)- Lead EngineerTiffany Heyd (ME)- Simulation EngineerBen Hensel (ME)- Test EngineerDr. Alan Raisanen- Faculty Guide

Special Thanks to:Phil Vallone of ITTRob Kraynik and the entire ME shop staffDr. Linda BartonDr. Marca LamDr. Mark KempskiDr. P. Venkataraman

P1156620101 / 20102

Customer Need Parameter SpecificationCritical to deliver prototype that matches analytical model.10-25% Damping Constant Zeta appropriate stiffness of system

Damping Coefficient Zeta 10% to 25%

½" range of motion mandatory, desired 1" Amplitude ±0.25" to ±0.50"

Component for space applications

Operating Temperature -40° C to 80° COperating Pressure Envelope 0 Pa

Has to last 10 years Lifecycle 158,000 cyclesWeight must be less than 10kg Mass <1 kgPayload to be damped is approx. 60 kg (system of 6 dampers) Load 10 kgSystem must not be affected by magnetic field beyond 6"

Magnetic Field Strength @ 6" from <20 mG @ 6"

Need to damp 1 Hz vibration in motion and 100 Hz vibration while

stationary

Frequency (maneuver) 1 HzFrequency (stationary) 100 Hz

No tin, zinc, or organic volatiles

Not suitable for space applications due to "whisker" formation and off

gassing.No Rubbing of Components

Very difficult to model "stick slip" occurrences.

Factor of safety of 2

Copper vane is free to move through magnet array.

Flexure constrains motion

Layers promote easy modification

Cast iron bridges magnetic field, amplifies power greatly

Known issues: • During testing it was difficult to find a consistent method to vibrate

the damper.• While exploring different options and trying different techniques, a

shift in the magnetic array caused rubbing.• It is unknown whether the model matches the prototype, or what

level the prototype was performing at before the array shift happened.

• Unit is very heavy, assumptions were made that the actual unit would contain aero grade materials.

• Unable to test at temperature extremes or in vacuum.

Proposed Work:• Use non-conductive magnetic bridge to make simpler magnetic

field.• Attempt to design to last for proposed life cycle.• Make continuous strides to reduce weight of the unit.• Consider designs that would reduce possibility of rubbing.• Consider trade off of swapping copper for aluminum conductor

(conductivity vs. weight).• Effect on damping coefficient from increasing magnet layers.

Test fixture with unit attached to shaker table …before the test caused the shaker to overheat.

Damping Force (lbf)

Damping Coefficient, c (lbf-s/in)

Spring Constant, k (lbf/in)

Zeta (%)

Experimental 0.65 1.31 82.87 7.25%

Theoretical 1.81 3.62 20.87 13.83%

Difference 64% 64% 297% 48%

Theoretical eddy current produced from conductor moving through a pair of magnets at 0.5 in./sec (from COMSOL).