Vibratory bowl feeder is the most versatile of all hopper feeding devices for small engineering parts and plays a key role in assembly automation. Decoupled vibratory bowl feeder is its new form, where torsional horizontal vibration and linear vertical vibration of the bowl are generated independently. Their performance very much depends on the driving signal forms. In this paper, a comparison has been made between the conventional vibratory bowl feeder and the decoupled vibratory bowl feeder in driving signals, which indicates that decoupled vibratory bowl feeder has the advantage of higher mean conveying velocity. Different driving signals are studied based on decoupled vibratory bowl feeder, and theoretical results show that square wave form has better effect than sinusoidal and triangular wave forms in terms of the mean conveying velocity.