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Implementation of robotics into welding is an important step towards higher productivity and better quality control of the fabrication process. However most robots currently perform welding in a "blind" fashion. In order to enhance the intelligence of the robots, several sensing techniques such as laser stripping, through-the-arc sensing and infrared thermography have been investigated. Most of these sensing techniques are capable of monitoring only a single welding parameter. However infrared thermography has shown promise t9 detect several types of impending weld defects. 1,4 The results presented in this paper identify approaches to obtain quantitative relationships to monitor the two major weld parameters, torch position and penetration depth. The asymmetry of the thermal profiles caused by an arc misalignment has been quantified into a torch seam error relationship by comparison of the features of thermal profiles on either sides of the calibrated torch position. To monitor the weld penetration depth the thermal distribution of the plates being welded were fitted to an ellipse using a least squares method. The principle features of the ellipse were found to be sensitive to the penetration depth of the plate being welded.

Penetration depth is a key variable, which needs to be controlled to ensure defect-free welds. One of the major problems involved with adaptive control penetration is the lack of suitable variables which can be viewed directly by the sensor. A proposed sensing technique is to relate the invisible variables, such as penetration depth and thickness of the welded steel plates, to visible variables of thermal images. The sensed infrared information was obtained through digital signal process of the thermal images associated with the high temperature of the molten metal pool and its vicinity during the welding process. Quantitative measurements were conducted to find a relationship between visible and invisible parameters. The thickness of plates being welded was varied and the corresponding changes in both penetration depth and surface temperature distributions were studied quantitatively. A least squares method was used to fit the obtained isotherms to an equation of an ellipse. The penetration depth and thickness of the materials being welded were found to be functions of the minor axes and the area of the ellipse for Gas Tungsten Arc Welding (GTAW). The experimental results can be used to achieve adaptive penetration depth control.

A scalar phase conjugator is used to correct for modal scrambling in a fiber-optic gyroscope using multimode fibers. A proof-of-principle demonstration of rotation sensing is reported.

The temperature dependence behaviour of the microbend-induced birefringences of single mode fibers has been experimentally investigated. It is found that the temperature dependence of the microbend-induced birefringence of an elliptically jacketed fiber is much smaller than that of a non-polarization preserving fiber. In agreement with the theory, measurements show that the temperature dependence of the birefringence can be interpreted using the photoelestic effect of the fiber, and the corresponding stress on the fiber due to the microbending can be deduced from the experimental data.

An all-fiber single-sideband frequency shifter has been demonstrated that uses a traveling acoustic wave incident upon a birefringent fiber at an angle to produce phase-matched polarization coupling. The fiber was helically wound on an aluminum cylinder to form a compact device. Conversion efficiency of 75% at 6 MHz has been obtained using 0.4 W of electrical input power. A 3 dB tuning range of 210 KHz was achieved. Sideband and carrier suppressions of 35 and 20 dB, respectively, have been observed.

A Michelson Interferometer using two photorefractive BaTiO 3 crystals was studied in which one BaTiO3 was used to generate a self-pumped phase-conjugate wave. This conjugate wave forms theone arm of the interferometer and was also used as one of the pumping beams to pump the other BaTiO 3 crystal which generated the other phase-conjugate wave through four-wave mixing. The output from the two arms are therefore both phase-conjugate waves. The interference pattern shows excellent spatial intensity distribution and is insensitive to the reciprocal noises and optical path length. Absolute phase of the phase conjugator was also measured which is a function of the crystal orientation and can be used to bias the interferometer by simply rotating the crystal to obtain an operating point of highest sensitivity and linear response.

Implementation of robotics into welding is an important step toward higher productivity and better quality control of the fabrication process. However most robots currently perform welding in a "blind" fashion. In order to enhance the intelligence of the robots several sensing techniques such as laser stripping, through-the-arc sensing and infrared thermography have been investigated. Most of these sensing techniques are capable of monitoring only a single welding parameter. However infrared thermography has shown promise to detect several types of impending weld defects. 1,2 The results presented in this paper identify approaches to obtain quantitative relationships to monitor the torch position with respect to the seam of the plates being welded. The asymmetry of the thermal profiles caused by arc misalignment has been quantified into a torch seam error relationship. Two principal comparison techniques have been identified. Averaging methods have been implemented to reduce the noise level in the error signals.