Determining alignment between threaded parts using force and position data from a robot hand

A technique for determining threaded part alignment using minimal force and angular position data is developed. This technique is based on backspinning a nut with respect to a bolt and measuring the force spike that occurs when the bolt "drops" into the nut. Kinematic models that describe the relationship between threaded parts during backspinning are presented and are used to show how angular alignment may be determined. The models indicate that it may be possible to distinguish between the aligned and misaligned cases between a bolt and a nut by using axial force data only. In addition, by tracking the in-plane relative attitude of the bolt during spinning, data can be obtained on the direction of the angular misalignment. Results from experiments using a bolt held in a Salisbury hand are presented.