This paper presents a model-based approach to the recognition of discrete state transitions for robotic assembly. Sensor signals, in particular, force and moment, are interpreted with reference to the physical model of an assembly process in order to recognize the state of assembly in real time. Assembly is a dynamic as well as a geometric process. Here, the model-based approach is applied to the unique problems of the dynamics generated by geometric interactions in an assembly process. First, a new method for the modeling of the assembly process is presented. In contrast to the traditional quasi-static treatment of assembly, the new method incorporates the dynamic nature of the process to highlight the discrete changes of state, e.g., gain and loss of contact. Second, a qualitative recognition method is developed to understand a time series of force signals. The qualitative technique allows for quick identification of the change of state because dynamic modelling provides much richer and more copious information than the traditional quasi-static modeling. A network representation is used to compactly present the modelling state transition information. Lastly, experimental results are given to demonstrate the recognition method. Successful transition recognition was accomplished in a very short period of time: 7-10 ms.

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