Presentation control for flat article singulation mechanism and sensors suitable for use therewith

An apparatus and method are provided for controlling the presentation of articles to the singulation head of a system for singulating a stack of edge-mounted articles, for example mixed mail, which mechanism senses the instantaneous pressure at which the lead article of the stack is pressed against the singulation head. A feedback control may be provided responsive to a difference between detected instantaneous pressure and a desired target pressure for controlling at least one drive member in a manner so as to reduce such difference. Where there is a pick window of instantaneous pressure at which singulation can be effectively performed, a control may also be provided to inhibit operation of the singulation head when the instantaneous pressure is outside the pick window. Two vertically spaced pressure sensors may be provided on the singulation head to detect the angle at which the lead article is presented to the head and controls may be provided for the drive mechanism(s) to reduce the difference between the instantaneous angle detected and an optimum angle for singulation and/or to inhibit operation of the singulation head when the instantaneous angle is outside of a range where singulation may be effectively performed. The sensor preferably includes a lever extending from the surface of the singulation head which is moved by a distance dependant on the pressure applied thereto. A servo motor may be connected to the lever to apply a bias pressure thereto which bias pressure is determined by a control signal applied to the motor. The sensor may also include a position encoder generating an output indicative of lever position.