Features
The OPTRA
NanoGrid is an XY planar encoder that measures the position of the
sensor head relative to an encoder grid with resolution and
repeatability up to the nanometer level. Unlike laser interferometers,
the NanoGrid is insensitive to air turbulence and is able to provide
extraordinary repeatability in real working environments.
The
NanoGrid Planar Encoder allows both X and Y position measurements to be
made at a single point, using a single laser diode sensing beam. The
relatively large physical separation between the sensor head and the
encoder simplifies installation.
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The NanoGrid A high-resolution planar encoder
consists of a single read head, a glass encoder grid and a two-axis
high-resolution phase processor. The phase processor is a full
size PCI-compatible plug-in card (PC only) that provides fast dual-axis
on-board processing of the analog signals generated in the sensor
head. Position information is available as a 32-bit parallel word
or an A-quad-B output. Parallel data are available via the PC bus
(for easy software access) or two 60-pin headers, for
direct high speed data reads at .305nm resolution.
The glass encoder grid captures the
accuracy of the laser
interferometer during manufacturing. The sensor head illuminates the grid
with a visible laser diode, collects the diffracted light and creates a
fringe pattern on OPTRA's patented tri-phase detector. The
combined system provides a position reading that is repeatable to
better than 2 nanometers.
Due to its relative insensitivity to yaw rotations,
the NanoGrid Planar Encoder can be combined with a second sensor to measure
in-plane rotations up to ±2°, providing a system for directly measuring all possible in-plane motions.
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The NanoGrid B Standard Resolution Planar Encoder features the coupling of the
NanoGrid planar position sensor with OPTRA's PolarFlash signal
processor module. The ASIC-based processor module features fast
dual-axis processing of the encoder position signals. Position information is in the form of an
industry standard A-quad-B digital signal. The edge rate and resolution
are selectable, ranging from 1.25 to 10 MHz and from 20 to 156nm,
respectively.
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OPTRA NanoGrid planar encoder grid plates fundamentally capture the
inherent accuracy of the laser interferometer in their manufacturing
process. The grid grating is a square pattern of 5µm chromium squares
on 10µm centerlines. When manufactured using this high precision
equipment, which is under interferometer control in a tightly
controlled environment, the accuracy of the grid grating can be held to
sub-micron tolerances. Unlike the interferometer, however, the grid
suffers none of the instability problems caused by environmental
perturbations, making it an ideal measurement tool.
A NanoGrid Planar Encoder captures the accuracy of the laser interferometer
in the manufacturing the encoder grid. The sensor head then collects
first-order diffracted light reflected from the encoder grid. Our patented
detector measures the interference pattern and results in an extremely
stable, balanced signal with a interpolation error of less then 10
nanometers.
OPTRA planar encoder grids can be manufactured on a number of different substrates
at various cost and accuracy levels. Standard sizes are available, and
grids can be cut to your exact size requirements for an additional fee.
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