Sensor location optimization for fault diagnosis in multi-fixture assembly systems

The effectiveness of fault diagnosis in assembly is contingent on the effectiveness of the sensor measurement of assembled parts. Using a diagnosability enhancement methodology for a single fixture, a means to achieve an optimal sensor configuration for a multi-fixture assembly of sheet metal parts is proposed. A Hierarchical Group description of the assembly is used to build a State-Transition representation which, with fixture CAD information, is used in multi-level hierarchical optimization to arrive at the optima. A defined Coverage Effectiveness Index quantifies fault isolation performance. The index also serves to evaluate the performance effectiveness of the measurement station location and change in the sensor number. The approach has significant utility in automotive body assembly where system complexity makes the choice of sensor location vital to fault isolation performance. Examples using multi-fixture simulated and industrial automotive body assembly sequences are provided to illustrate the methodology.