Multisensor-Based Detection of Contact State for Automated Sheet Metal Assembly

Abstract Sensor information is important for the control of automated sheet metal assembly. In this paper a multisensor-based system is developed to detect the contact state of a lap joint between two sheet metal workpieces. The contact states detected are: left end, right end, full contact, and no contact. Detection methods are developed based on the use of a Force/Moment Sensor (FMS), novel Strain Gauge equipped Fingers (SGFs) and sensor fusion of the FMS and SGF information. It is shown that a trade-off exists between the detection time and the detection success rate. The methods are verified in 120 robotic assembly trials. The success rate for the FMS method increased from 63 to 88% when the sheet thickness was increased from 0.69 to 1.88 mm (gauge 23 to gauge 15). Under the same conditions the success rate for the SGF method decreased from 90 to 55%. The sensor fusion method surpassed the best individual performances of the other methods by achieving a 100% success rate for the complete set of sheet thicknesses and contact states.