The Principle

An essential point in the research and teaching activities are vibration analyses of structures. A wide variety of sensors, actuators including controls and measuring amplifiers are available for determining modal properties. By attaching sensors, an additional mass is applied that influences the vibration behaviour of the object under investigation. This side effect is undesirable when determining or validating model parameters for simulations or when designing controlled systems and is particularly problematic when investigating small, lightweight structures.

For a good non-destructive investigation of small to medium-sized structures, a laser scanning vibrometer (PSV-500-H8) is used which, in addition to the non-contact recording of vibrations, also enables the determination of transfer functions, modal parameters (natural frequencies including the associated damping). With this measuring system, vibration velocities can be determined in the direction of the laser beam - usually normal to the measured surface. The scan head contains an HD video camera and a measuring laser. Via a mirror system, the laser beam can be directed to arbitrarily definable points on the measuring surface ranging from a few mm² to several m² and record the vibrations of the structure. The subsequent analysis enables the display and animation of the individual vibration forms.

Figure: Laser-Scanning-Vibrometer measurement system

Application in Practice

• Materials testing
• Acoustics
• Determination of modal parameters as a basis for modelling and for the validation of simulations

Video: Setup a Measurement with PSV500

The following video shows the basic setup for a measurement with the laser scanning vibrometer. A simple CD-ROM is used as the test object. This was sprayed with a chalk spray before use so that the optical reflection is as strong as possible at all measuring points.

Courses

• LU Mechatronic Systems Lab
• VU Modal analysis

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