Vibration is a back and forth mechanical motion with a steady, uninterrupted rhythm about an equilibrium point. There
are two types of vibration; natural (or free) and forced. Natural vibration occurs as the result of a disturbing force that is
applied once and then removed. Forced vibration occurs as a result of a force applied repeatedly to a system. All
machines have some amount of forced vibration. However, in some cases this vibration can cause damage to machinery.
Understanding vibration is essential for any system that will be exposed to motion. Equipment such as strain gauges and
piezoelectric accelerometers have been adequate in measuring vibration in the past; however, due to increased
performance requirements and subsequent reductions in vibration, these methods are slowly being replaced by laserbased
measurement systems. One reason for the slow transition is that part of the system in these methods must be
mounted on the surface of the object being measured which can change the mass thus alter the frequency and mode
shape of the vibrating object. At this time however, the high expenses to monitor precision vibration is a challenge, and
there is a need for more cost-effective methods of vibration analysis. This paper outlines a lower cost laser-based method
of measuring vibration with minimum surface contact.
The need for improved thermal efficiency of jet engines has led to changes in the design of combustor turbine blades.
Modern turbine stage inlet temperatures now exceed the melting point temperatures of turbine blade materials. Super
alloys, based on nickel, have been developed for use as blades, guide vanes, afterburners etc. To combat and avert blade
failure caused by excessive operating temperatures, film cooling has been incorporated into blade design. In film
cooling, cool air is bled from the compressor stage, ducted into internal chambers of the turbine blades, and discharged
through small holes in the blade walls. This provides a thin, cool, insulating blanket along the external surface of the
turbine blade, and large numbers of shaped holes have allowed designers to maximize the cooling effect.
This paper explores a new design for measuring the presence and depth of blind holes in turbine blade. In the paper, we
examine the inspection techniques currently in use and present a novel optical technique as an alternative. To precisely
locate and measure the holes on the turbine blade, an XYZ translation stage is employed. Using a small collimating tube,
a micro-beam illuminates each hole in a pre-programmed fashion. Depending on the level of reflected intensity and
when it occurs, the presence of a hole bottom is determined. The optical inspection system consists of a laser, motorized
micro-positioning stage, collimating tube, optical detector/amplifier, data acquisition software and a customized fixture for manipulating the samples.