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Analysis of a new fiber optic sensor based on the principle of Fresnel reflection is presented in order to develop a robust, flexible, readily embedded, high sensitivity and low-cost cure monitoring tool for intelligent control of composite manufacturing. This approach is distinct from previous work on on-line in-situ monitoring sensors in that the transducer is simply the fiber optic/epoxy interface. This leads to a more simple, less intrusive, and lower cost sensing system. The response of the sensor is a function of the mismatch in refractive index between the fiber optic end/resin interface. The refractive index of the resin is a nonlinear function of the temperature and the cure reaction of the resin. The sensing system detects the mismatch in the refractive index and generates a characteristic profile that gives the chemorheological information about the curing resin. Under isothermal cure conditions, the effect of the temperature on the refractive index mismatch can be eliminated. In this situation, the optical response of the sensor is only dependent on the cure kinetics and the state of the cross-linking in the material. A calibration method has been developed to interpret the optical response directly as the degree-of-cure of the resin. This work provides analysis of the fundamental sensor response and correlates it to the material state (degree-of-cure). These results provide a basis for extending the use of this sensor technology for on-line real-time cure monitoring and control.

Purpose -The purpose of this research is to develop closed-loop control of robotic welding processes. Design/methodology/approach -The approach being developed is the creation of three-dimensional models of the weld pool using stereo imagining. These models will be used in a model-based feedback control system. Fusion of more than one sensor type in the controller is used. Findings -Three-dimensional images can be produced from stereo images of GMAW-p weld pools. This requires coordinating the image capture with the arc pulse to allow observation of the pool. Research limitations/implications -This is a work in progress. The imaging is not being done in real time at this point in time. Future work will address this issue. Also, how the image information is to be used to make corrections within the controller is future work. Practical implications -Closing the loop on GMAW welding will allow robotic automation of welding to proceed to a much broader degree of application. Originality/value -This paper demonstrates that stereo imaging of out-of-position GMAW-p weld pools is possible and the useful information can be obtained from these images. It also provides insights into the analysis required within the model-based controller if one is to close the loop on the process specifically with regard to weld pool stability.