The use of collaborative robots (cobots) in the industrial setting has grown and continues to expand globally, especially in the context of the smart factory. Mistrust and stress results, as cobots don’t provide facial, auditory, and visual cues that workers normally use to predict behavior. For quantification of mental stress, physiological, behavioral and subjective measures are integrated, processed and analyzed in a smart factory lab setting. The impact on the human workers as mental stress and fatigue conditions are correlated with the task complexity, speed of work, length of collaborative task and cobot payload etc. Multimodal functional neuroimaging was used to record participants’ neural and cardiac activity, in addition to the standard subjective and behavioral measures as they collaborated with robots in multitasking contexts. Preliminary results show that task complexity is positively correlated with beta and gamma band power, left prefrontal cortex activation, and heart rate, while it is negatively correlated with alpha band power during task performance.