ENG 0310 Design ProjectContest: Base Isolation System

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ENG 0310 Design Project/Contest Base Isolation
System
Goal design a spring/dashpot suspension system
to hold a laser as steady as possible on a
vibrating base.
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Topics

• Examples Basic Concepts
• Theory
• Design parameters additional notes
• Organization and important dates

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Topics

• Examples Basic Concepts
• Theory
• Design parameters additional notes
• Organization and important dates

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Vibration Control Base Isolation
Soft, Springy Mount
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(No Transcript)
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The Christchurch Arts CenterWith and Without
Base Isolation
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Other Suspension Systems (same idea) Keeps
equipment steady while the supports vibrate!
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Cars
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Printed Circuit Board Manufacture
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Everyday examples
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Commercial Product of Vibration damping
http//www.newport.com/
An optical table is a stiff platform supporting
vibrationsensitive equipment. A typical optical
table is a sandwich structure consisting of two
faceplates and a lightweight honeycomb core. Due
to high stiffness-to-weight ratio, these
platforms are used in a wide variety of
applications in optical research and
high-precision manufacturing, usually in
conjunction with soft pneumatic vibration
isolators. Although good isolation from floor
vibration can be achieved in these systems, the
platform deviates from the ideal rigid-body
behavior at natural frequencies of its flexural
vibrations. These higher frequency flexural
vibrations cause misalignment of optical
equipment installed on the table, which leads to
deterioration of the optical performance.
The table's legs are pneumatic vibration dampers!
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Topics

• Examples Basic Concepts
• Theory
• Design parameters additional notes
• Organization and important dates

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Free vibrations
C

• Vibration occurs at the system-dependent natural
  freqency.
• The oscillations decay exponentially (if
  )
• Initial condidtions x0x(0) and v0 v(0)
  determine the amplitude and phase

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Forced Vibrations Periodic forcing
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Typical Response
Displacement
Time
Transient vibrations xh(t) at the natural
frequency. Depend on I.C. These decay
exponentially with time.
Steady-state Vibrations xp(t) at the forcing
frequency Independent of I.C. These do not decay.
Total response x(t)xh(t)xp(t)
Amplitude of the steady-state vibrations is
(very) large if the forcing frequency is at or
near the system natural frequency.
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The Steady State Response Damped
C
Amplitude X/(F0/k)
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Vibration under base excitation
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Base Excitation
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Base Excitation
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Steady state response
Displacement
Time
Transient vibrations xh(t) at the natural
frequency. Depend on I.C. These decay
exponentially with time.
Steady-state vibrations xh(t) at the forcing
frequency Independent of I.C. These do not decay.
Steady state response
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Amplitude of the steady state response
Isolation
Amplitude X/Y
Amplification
w/wn
Pick a (soft) spring so that (wn)2k/mlt w2/2. Use
light damping
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Topics

• Examples Basic Concepts
• Theory
• Design parameters additional notes
• Organization and important dates

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• Design parameters
• The laser is the Apollo MP2703B Classic Comfort
  Laser Pointer (Figure 2). Its mass is 49 g is
  13 cm long and has a diameter of 1.4 cm.
• The table will vibrate over a range of
  frequencies fw/2p from 0 to 7 Hz, or 0ltwlt14p
  radians/sec. The peak-to-peak amplitude of motion
  for the table is 2Y0.6 cm.
• You must be able to affix your isolation system
  to the square surface of the shake table, which
  has side length 0.3 meters.
• Your laser will project its beam onto a screen
  b1 meter from the table edge.
• When the table is shaken at frequencies of 5 Hz
  or higher, the peak-to-peak amplitude A2X of the
  lasers projection on the screen must be less
  than 0.3 cm. The best designs will hold the laser
  beam to an even smaller displacement
• When the table is shaken at frequencies below 5
  Hz, the peak-to-peak displacement of the lasers
  projection must be less than 2.4 cm.
• Minimize the weight.

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Note on the Spring-Mass Frequency
mg
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Works for any spring system!
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Car Suspension

• Wheel Motion
• Isolation when (wn)2k/mlt w2/2(2pv/L)2/2
• Typical car fn1 Hz wn2p radians/sec
• Isolates for bump-spacing Lltv/ meters. (v in
  meters per second)
• If v25mph10m/sec maximum bump spacing is 7
  meters

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Topics

• Examples Basic Concepts
• Theory
• Design parameters additional notes
• Organization and important dates

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Important Dates

• Monday, November 16 Submit names of group
  members (via email Huajian_Gao_at_Brown.edu) and
  team name on paper before 4pm. Maximum of 6
  students per group.
• Monday, November 23 Submit preliminary design w/
  drawings.
• Fabrication can start as soon as the design is
  submitted.
• Friday, December 11 Final demonstration/contest
  (Prinz Lab) Final reports due.