Cabin parts Car Body Vibration

Car Body Vibration

The demand to reduce the overall noise level in and outside the car requires detailed knowledge about the vibration behaviour of the different components. The analysis of car body vibrations is especially laborious, because the large areas require many measuring points. With standard techniques extensive and costly analysis work is used.

Pulsed holography techniques have been used for this purpose, too, but the laborious chemical processing of film material and the rather qualitative data output limited its application in industry. Recently, pulsed holography could be replaced by digital techniques, Pulsed Electronic Speckle Interferometry (PulsESPI), which is a non contact measuring technique and provides full field information about displacements in very short time.
 
Pulsed ESPI

The pulsed ESPI technique allows to record two different states of a vibrating object with very short time intervals and compare these states quantitatively. In order to do so, the object under investigation is illuminated twice by the very short light pulses of a pulsed laser.

A high speed camera records the two images of the laser illuminated object and stores them on a computer. From these two images the quantitative displacements of each object point in the field of view is automatically calculated in few seconds. The measuring sensitivity of the system is ca. 30 nanometer.
 
 
Ruby laser

The most popular laser for PulsESPI applications is a ruby laser, which can fire two laser pulses with between 2 and 800 microseconds pulse separation time. New laser designs nowadays allow the production of relatively small and portable systems. The camera can directly be integrated into the laser head and no adjustment is required for operation. The new laser generation is completely computer controlled and makes the PulsESPI system easy to operate.
 
 
Trigger of laser

The trigger of the two laser pulses with respect to the vibration signal is of great importance for the vibration measurement. Generally, a signal of a local accelerometer or of a vibrometer is used to trigger the laser. Beside  the complete electrical system for triggering of any event is displayed.

If, e.g. in car body vibration analysis the object is excited sinusoidally with a shaker, the signal can directly be used for precise triggering of the laser. The laser pulses can be triggered to the maximum and minimum of the vibration or to any other time required.