What I did: measure the transfer function from coil magnet actuator to photo sensor.

I measured the Roberts Linkage's transfer function from coil magnet actuator to photo sensor.
First of all, I attached magnets on the suspended mass, and also set a coil.
Fig 1, 2, 3, 4 is a setup of coil magnet actuator.

When I measured the transfer function, the data was measured from 0.1Hz to 10Hz and also measured form 10Hz to 0.1Hz.
The reason is that a resonant osillation of Roberts linkage remained for a while, so I can't measured the trasfer function appropriately after passing throught the resonant frequency.

Fig 5 is the transfer function when I measured it from 0.1Hz to 10Hz.
Fig 6 is the transfer function when I measured it from 10Hz to 0.1Hz.
Fig 7 is combined one.