Using a TDI camera in vibration conditions with nonzero viewing angles for surface inspection

A variety of Time Delay and Integration (TDI) arrays have been developed. The TDI image sensor offers significant improvement in performance over a linear CCD-sensor with respect to sensitivity. This is particularly significant in low light level operation since the effective exposure time is increased by a factor which is equal to the number of the TDI stages in the sensor. Our previous work has indicated that the TDI camera can be used with viewing angles up to 30 degrees from the surface normal. The effects caused by vibration of the viewed surface become critical when using a TDI camera at non-zero viewing angles. For this rfeason, a study was made on the vibration effects. This paper reports this study, concentrating on the relation between the vibration of the inspected surface and the sharpness of the image. The contrast perceived by the TDI camera as a function of the vibration amplitude and frequency is measured. The measurements are performed using a special test pattern in a dynamic situation. The results based on the contrast modulation function (CMF) in the vertical and horizontal directions are reported. A hypothesis of the effect of vibration on the CMF was formulated as a rule, which was then tested with measured data. Tentative result support the hypothesis.