PROJECTS: SMART STRUCTURE
makezine.com/13/structure
NEGOTIATING A STANDSTILL
HOW IT WORKS
Our aluminum beam “skyscraper”
has 2 piezoceramic actuators
glued flat against its base, on
opposite sides. On one side, just
above, is a piezoceramic sensor.
1 The sensor is smaller and only needs to
be on one side because it detects flexing in
both directions.
2 The actuators are on both sides because
they have more work to do. They flex out of
phase, with one side shrinking as the other
expands. This action applies a moment to
the beam that induces bending.
3 The phase switch swaps the signals to
the actuators to make them move in the
exact opposite direction.
The smart structure’s circuit is based on an
LM324 quad amplifier chip.
4 The lower left amplifier (I/O 2) works as a charge
amplifier, a circuit routinely used to buffer charge
from a piezo onto a capacitor to be measured.
5 The upper left (I/O 1) is a low-pass filter
that boosts the input’s low-frequency vibrations
(~24Hz), which match the beam’s first resonance.
It also converts displacement into velocity by
shifting back the phase, as explained below.
6 The chip’s right side (I/O 3 and 4) forms a
bridge amp that powers the tandem actuators 180°
out of phase, over a range of ±36V.
5
4
6
1
2
2
3
For complete
schematic and wiring diagrams, plus
videos of the smart
structure in action,
see makezine.com/
13/structure.
Our beam exhibits
sinusoidal vibration,
which occurs whenever
something is pulled
back to its resting
position with a force
that’s proportional
to its displacement.
The sensors measure
displacement, but
to damp vibrations
you need to counter
velocity, which is
the first derivative
of displacement. So
our circuit does some
calculus, but with
sinusoidal vibration
this is easy: just shift
the phase back 90°.
Illustration by Nik Schulz
136 Make: Volume 13
