Emotions are the intrinsic or extrinsic representations of our experiences. The importance of emotions during a human-human interaction is immense as it formulates the basis of our interaction framework. There are several approaches in psychology to evaluate emotional states in humans based on the perceived stimuli. However, the topic has been less explored as far as human-robot interaction is concerned. This paper uses an appropriate emotion appraisal mechanism from psychology, generating an emotional state in a humanoid robot on-the-fly during human-robot interaction. Since the exhibition of only six basic emotions is not sufficient to cater to diverse situations, the use of the Circumplex Model in this work has allowed the life-sized robot called ROBIN to experience 28 emotional states in different interaction scenarios. Realistic robot behaviour has been generated based on the proposed appraisal system in various interaction scenarios.