(^128) PART 2 HOW DIGITAL CAMERAS CAPTURE IMAGES
Piezoelectric Supersonic Linear Actuator
Stabilization
A microprocessor inside the camera body receives
movement information from the angular velocity
sensors mounted next to the imaging sensor. One
digital gyroscope is positioned to detect only verti-
cal movement; the other detects only horizontal.
The microchip combines the information to get a
two-dimensional picture of camera motion,
although the microchip cannot compensate for for-
ward and backward motion, which has a smaller
effect on photo sharpness.
The microchip sends electrical signals of its own to two piezoelectric super-
sonic linear actuators—also known as SIDMs, for smooth impact drive
mechanisms. Like the movement sensors,
the SIDMs are mounted at right angles to each
other to handle vertical motion (the Y-axis actuator) and
horizontal motion (the X-axis actuator).
When current reaches an actuator, it’s directed to a
piezoelectric element mounted between a weight and a shaft. The
current causes the piezo to expand or contract, depending on
the direction necessary to make the correction. The shaft moves
slowly at first because the weight is designed to hold it back.
Each of the actuators’ shafts presses against a different plate holding the
image sensor. One plate is free to slide vertically while the other can move hor-
izontally. Only friction connects the shafts to the plates, which is
one reason for the initial slow movement of the shaft—so the
movement doesn’t overcome friction and cause a shaft to lose its grip on the
plate. (Actually, this talk of slowness is deceptive. Because these corrections
happen in a few thousandths of a second, any “slowness” is purely relative.)
When the image sensor is in its new, corrected position, the shaft withdraws
by contracting or expanding quickly so as not to take the correctly positioned
image sensor with it, like a tablecloth being jerked off a table so fast it leaves
the table settings in their places.
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Most digital cameras with anti-shake mechanisms try to
bend the errant light rays as they pass through the lens so
they still strike the correct pixels on the image sensor. It’s
like trying to deflect an arrow on the way to its target. A
year or so before Konica Minolta got out of the camera
business, it patented an attack on the shakes that takes the
opposite tact, as if some poor loser were forced to hold
the target and move it to wherever the arrow’s coming in.
To achieve this, Konica Minolta had to develop new tech-
nology throughout the process—technology now in the
hands of Sony, which bought Minolta’s camera business
and is now showing up in other digicams as well.
Motion Correction
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