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Voice
coil driven Fast Steering Mirrors (FSM) have been used for several years in
military and aerospace applications for target acquisition, scanning, and beam
steering. These mirrors were
typically low volume – high cost parts. Optics-In-Motion
has engineered a line of fast steering mirrors which have many of the attributes
of the military versions (low noise, high pointing accuracy, and high
acceleration/step speeds) but are available at commercial prices.
Two Inch Glass Fast Steering Mirror
(clear anodized for vacuum applications)
The
100 series fast steering mirror product line consists of a one inch glass
version with a user replaceable mirror/sub-mount, and a two inch glass mirror
version where the mirror is hard mounted to the mirror gimbal, and a elliptical
two inch by three inch metal mirror.
Model
OIM101 Mirror key features:
ü
Uses industry standard 1” x 0.25” (or 1” x 6mm) glass
mirrors
ü
Mirror coating to customer requirements
ü
Mirror mounted into sub-mount using low out-gassing RTV
ü
Additional sub-mount available for user installation of mirror
ü
Wave-front quality 1/10th wave p-v (depends on mirror substrate)
ü
Useable aperture 0.94”
Model
OIM101
(Shown
with the standard 1" aluminized glass mirror)
Model OIM102 Mirror key features:
ü
2” glass mirror mounted to gimbal using low out-gassing RTV
ü
Mirror coating to customer requirements
ü
Wave-front quality ¼ wave p-v
ü
Useable aperture 1.95”
Model OIM102.3 Mirror key features:
ü
2” x 3" metal mirror
ü
Mirror surface either diamond turned or replicated
ü
Mirror coating to customer requirements
ü
Wave-front quality 1/2 wave p-v
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Useable aperture 2” x 3" or 2" at 45 degrees
Both mirror models are driven
by a push/pull configuration of voice coils (similar to speaker coil – magnet
arrangement). However unlike a
speaker the FSM is configured with a moving magnet instead of a moving coil.
This arrangement has several advantages.
The first being that since the coil is stationary the wires do not have
to move which adds greater overall reliability.
The second advantage is that the heat generated by the mirror coils is
conducted to the mirror housing away from the optical mirror substrate.
This prevents thermal distortions of the mirror wavefront quality.
Voice coil actuators are two wire
non-commutated direct-drive, hysteresis-free, cog-free devices used for
providing highly accurate linear and rotary motion. By virute of their high
acceleration and the absence of commutation, they offer numerous advantages in
high precision applications. They deliver infinite position sensitivity, limited
only by the encoder used for feedback. The force-versus-stroke curve is
perfectly smooth. It all adds up to increased throughput for your system.
The mirror is flexurally
suspended in two axes. The flexure
is designed for an infinite fatigue life under normal operation (the absence of
high levels of external vibration). The
mirror rotates in both directions around a single pivot point.
The pivot point for model OIM101 (1” mirror) is located 12mm behind the
mirror surface and for model OIM102 (2” mirror) the pivot point is 9.5mm
behind the mirror surface.
Local Position – the
mirror has a built in optical position sensor.
The position sensor provides mirror feedback information to the
controller which can also be monitored by the user.
The local position sensor outputs a voltage which is proportional to the
mirror angular position. The
position sensor scale factor is 10volts = 1.5 degrees (26.2 mrad) and has a
range from +10 volts (+1.5 degrees mechanical +3.0 degrees optical) to -10 volts
(-1.5 degrees mechanical, -3.0 degrees optical).
External Position –
the mirror controller has inputs for a user supplied control signals.
Typically these signals are from an external quadrant cell which is used
to monitor the position of a beam reflected off the surface of the fast steering
mirror. These external signals (x
and y position angles) are differentially input into the mirror command
connector. A TTL level high input to
the command connector INT/EXT switch controls the source of mirror feedback,
switching it from local to external position control.
The
mirror
controller electronics are housed in a remote enclosure connected to the FSM
via a 6 foot cable. Mirror
commands are input to the controller through a 25 socket D sub-miniature
connector. The commands are
differential signals representing the x and y mirror positions, scaled to the
+/- 10 volt range. Monitor signals
are provided for the actual mirror positions, error signals (feedback error
between commanded position and actual position), and temperature overload (TTL
signal with high representing a mirror thermal overload condition).
The controller is powered by an
external
tabletop +/-15 volt power supply (model number SRP-30A-2005) capable
of 1.5 amps of current. The external power supply is an air cooled
tabletop supply which plug directly into a 110 or 220 volt wall socket.
Mirror Performance:
Here is a typical Bode plot from our 1" glass fast steering mirror.
Closed Loop Bode Plot
3dB Bandwidth = 870 Hz
Gain Peaking = 1.3 dB
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