Inertial Electrodynamic shaker working principle
Inertial Electrodynamic shakers
Inertial electrodynamic shaker is very similar to the voice coil which is used in speakers.
Figure 1: Voice coil cross section
Voice coils work according to the Newton’s second law: F=ma
The inertial shaker is slightly different compared to voice coil but works with the same equation. The armature is the moving mass “m”. IS-40 has an armature weight of 0.16kg. When a signal is passed through the coil, it moves the armature up and down with an acceleration “a”. The multiplication “F” is the force rating of the inertial shaker.
Figure 2: IS-40 cross section
The armature is guided concentrically and suspended with two springs. Thus, it can be used at any orientation.
Figure 3: IS-40 Armature displacement limits
The armature can move up 4mm and down 4mm at most. This is a very important parameter as it limits the low frequency response of the inertial shaker.
Figure 4: Shows the theoretical and measured force response curves of IS-40
The theoretical curve does not take into account for any resonance, damping or impedance increase of coil with frequency. This is the main reason for the variation between them. Furthermore, at low frequencies the stroke of the armature is big. Thus, the spring slows down the armature too much which further reduces the acceleration of the armature and lowers the force levels.
The main reason for not having high force values at low frequencies is due to the displacement limit of the armature. The displacement must be very high if 40N at low frequencies is required. For example, if 40 N at 10 Hz is required then the displacement of the armature must be 64mm upwards and 64mm downwards compared to 4mm.
This is a common problem for electrodynamic shakers. That’s why, for high forces in low frequencies usually hydraulic actuators are used.
Inertial Electrodynamic shaker frequency response plot generation:
The frequency response plots of the Inertial shakers are obtained with a setup given in Figure 5.
