[Yokozawa, Ushiba]

Abstract:

We installed resistances between coil driver and IM coils to reduce the actuator efficiency.
Though actuator efficiency was reduced by -17dB, peak height around 40Hz doesn't seem to be reuced.
So, IM actuator noise doesn't seem to be the noise source around 40 Hz.

Detail:

To confirm IM actuator noise kicks the resonances around 40Hz, we installed the resistances between coil driver and IM actuators (fig1).
Resistance are 940 Ohms for each coil, which corresponding to the actuator efficiency reduction by 150/(940+150) ~ 7.2.

For confirming how much AE reduction happens, we measured the transfer function from COILOUTF excitation to OpLevs.
Since H1, H2, H3 actutor can move the suspension in yaw, TM yaw OpLev signals are used for checking AE reduction.
For V1 and V3, TM pitch signas are used while MN roll OpLev was used for V2 because V2 actuator can excite only roll motion.
I used excitation at 3.5Hz and 2Hz for horizontal and vertical AE measurement, respectively.

Figure 2 shows an example of AE measurement.
Blue and green lines show the TF from COILOUTF excitation to OpLev signals before and after installation of resistances, respectively.
Red line shows the TF from COILOUTF excitation to OpLev signals after the installation with compensation gain at FM9 (gain) of COILOUTF.
The measurements for the other actuators are also stored at the same directry.

The measured AE reduction ratios are about 7.2 - 7.5, which is almost same as we expected from the resistance values.
Then, I compared the DARM error signals before and after installation but no significant change can be observed around 40 Hz.
So, IM actuator doesn't seem the noise source around 40 Hz.