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Inspection of the Integrity of a Multi-Bolt Robotic Arm Using a Scanning Laser Vibrometer and Implementing the Surface Response to Excitation Method (SuRE)

The integrity of a robotic arm was examined remotely via a scanning laser vibrometer (SLV) in order to detect loose bolts. A piezoelectric element (PZT) was bonded on the robot arm for excitation of surface guided waves. A spectrum analyzer generated surface waves within the 20-100 kHz range. The propagation of the waves was monitored with the SLV at the programmed grid points on the robot arm.The surface response to excitation (SuRE) method was used to calculate the spectrums of the signals, and compare the reference scan with the altered scan. Comparisons of before and after the scan showed that after loosening the bolt on the robot arm, spectrums of all the grid points changed to some extent, however, the largest changes occurred in the vicinity of the loosened bolts.The study shows that the SuRE method was capable of detecting the presence and location of loosening bolts using only one PZT element on a complex structure. There are two most important advantages of the SuRE method over the widely used impedance-based technique. The first advantage is the elimination of an expensive impedance analyzer; the second advantage is remotely monitoring capability as long as the surface is excited properly.