Smoothie: Bell-Everman's new Z-axis
Bearing limits tilt to 1 arc-sec and handles travel of 25 mm or
Like a window shade, this Z-axis bearing unwinds thin, 0.003-inch strips, or
flexures, as it moves, achieving high parallelism without backlash, friction, or
rolling contact. Designer Michael Everman Inc. claims that the bearing's top and
bottom surfaces can be held parallel within 1 micron through a stroke. The
bearing can move nearly half the height it stands, making for a compact setup.
Laser welding attaches the flexures to the rollers. Three flexures per roller
are sized and oriented to equalize their spring constants.
Bell-Everman aims the bearings at semiconductor metrology, where optical focusing requires silicon wafers to move vertically in small nanometer increments. Low angles of tip and tilt are necessary to maintaining focus. Today, such optical focusing typically relies on two stages. A wedge screw makes any coarse moves. Then, a piezoelectric stage handles fine moves of up to 0.5 mm. Tilt during translation usually falls between 10 and 15 arc-secs in these stages. The new bearing limits tilt to 1 arc-sec and handles travel of 25 mm or more.
The company plans to offer the bearing with voice coil, piezo, or ball screw drivers. Any driver could be used, but the company recommends one that complements the bearing's knack for working clean and being maintenance-free.
At the Design News webinar on June 27, learn all about aluminum extrusion: designing the right shape so it costs the least, is simplest to manufacture, and best fits the application's structural requirements.
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