Combination of Fulcrum and FFT module

The com­bi­na­tion of the new Vic-3D FFT-Mod­ule and the known syn­chro­ni­sa­tion / trig­ger device with Ful­crum mod­ule of isi-sys GmbH / Cor­re­lat­ed Solu­tions INC for Vibro­cor­re­la­tion per­mits full modal and vibra­tion analy­sis using con­ven­tion­al low speed cam­eras. It can be applied on objects with high fre­quen­cy exci­ta­tion, which can replace High-Speed (HS) cam­eras, when con­ven­tion­al shak­ers are used for excitation.

 

Excitation signal

A peri­od­ic vibra­tion sig­nal with a wide fre­quen­cy spec­trum (e. g. chirp, fast sweep) is applies to a struc­ture via an elec­tro­dy­nam­ic, hydraulic or piezo shak­er. The cam­eras of a stereo­scop­ic sys­tem are set to a short expo­sure dura­tion (we use 200μs here) and they are trig­gered though the Ful­crum mod­ule of Vic-Snap.

The exci­ta­tion sig­nal is shown in the images below. A pulse is gen­er­at­ed by the func­tion gen­er­a­tor for each cycle of the exci­ta­tion (chirp) sig­nal and con­nect­ed to the syn­chro­ni­sa­tion device below.

Image 1 — Fre­quen­cy spectrum

Image 2 — Exci­ta­tion signal

 

Synchronisation

 

The cam­eras are trig­gered through the stan­dard synchronisation/trigger device  DAQ-STD-8D con­trolled by the Ful­crum Mod­ule for Vic-Snap/ Vic-3D.

 

 

FFT Module Evaluation Examples

The fol­low­ing results show the work­space of the FFT Mod­ule in Vic-3D with ampli­tude (left) and phase (right). Shift­ing the fre­quen­cy val­ue in the graphs below (ampli­tude or phase vs fre­quen­cy) per­mits to select the cor­re­spond­ing mode shape for any analysed fre­quen­cy. The ampli­tudes (left) are dis­played here as 3D plot, oth­er options are e.g. gen­er­a­tion of ani­mat­ed videos of the mode shape vibration.

The results on a sqare plate 140 x 140mm of dif­fer­ent res­o­nance fre­quences are shown in the images below.

Image 3 — Res­o­nance at 263 Hz

 

Image 4 — Res­o­nance at 707 Hz

 

Image 5 — Res­o­nance at 875 Hz

 

 

Application example of the FFT module:

Oper­a­tion mode analy­sis on a mobile phone dur­ing vibra­tion alert