Schematic overview of the suspended optic with the 6 degrees of freedom shown (yaw, roll, transverse, vertical, longitudinal, and pitch). Centre of mass (CM), the two hexagonals (blue) are local “ground,” and the circle (green) are wire clamps.
An engineering rendering of the tip-tilt mirror.
Single blade units with height adjuster.
A cross section of the aluminium ring with flags and the BOSEMs. Visible in the BOSEM are the photodiode, LED, and coil. The flag is attached to the aluminium ring with the magnet press fitted into it.
Tip-tilt longitudinal transfer function, driving the four BOSEM coils, and reading out the shadow sensors. The coils were driven, and the sensors were readout, uniformly.
Tip-tilt pitch transfer function, the top two coils are driven in a positive direction, while the lower two coils are driven in a negative direction. The shadow sensors are read out differentially between the top pair and the lower pair.
Tip-tilt yaw transfer function, the left two coils are driven in a positive direction, while the lower two coils are driven in a negative direction. The shadow sensors are read out differentially between the left pair and the right pair.
Hysteresis of the tip-tilt mirror suspension measured using the shadow sensors in the BOSEMs, (a) pitch hysteresis and (b) yaw hysteresis. The start and stop position is indicated by an arrow. Offsets were first increased to a positive maximum before cycling through a minimum and back to zero. The turnarounds of the measurements are due to the sensor limits, and do not represent the actual motion of the optic. The residual is shown between the forward and backward offset, when going through the cycle (scale on the right-hand side of each graph).
Tip-tilt mirror suspension pitch and yaw angle per applied coil current (modelled), using ø2 mm × 3 mm long magnets.
Measurement of the viton o-ring damped vertical blade resonance (bounce) as well as the roll mode resonance of a single suspension blade (while installed within the tip-tilt mirror suspension assembly). Included in the graph is the fitted model with the results listed in the legend. The o-ring damping has reduced the vertical mode resonance to 67 (down from 180).
Measured modal response of the tip-tilt structure.
Basic tip-tilt mirror suspension mechanical parameters.
Basic tip-tilt mirror suspension modelled and measured eigenmodes.5
The vertical blade parameters and modelling results.
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