Abstract: A sheet counting apparatus includes a set of rotatably mounted suction spindles mounted for movement past a stack of sheets to be counted. A pump is connected to the spindles whereby a suction spindle passes the stack, a vacuum is supplied to the spindle so that the topmost sheet is deflected from its initial position. A monitoring system monitors the number of deflected sheets by monitoring the degree of vacuum within the suction spindle passing the stack. The monitoring system increments a count on each occasion when the monitored vacuum exceeds a predetermined threshold. The monitoring system terminates the count process when a predetermined period is exceeded without the vacuum exceeding the predetermined threshold, the predetermined period corresponding to the passage of at least two spindles past the stack of sheets, without the spindles deflecting a sheet.

Abstract: Apparatus for sensing the passage of sheets (1) through a nip formed by rollers (5 and 6), includes means for sensing the deflection of one roller relative to the other, the sensing means including an oscillator (18) providing a train of signals the frequency of which varies with the amount of the relative deflection of the rollers, and a counter (19) counting the signals from the oscillator in a fixed time interval. Means (23) are provided for storing counts representing the relative deflections of the rollers in a cycle of movement of the rollers when no sheet is present, and for comparing the difference between a subsequent count and a stored count for a corresponding position in the cycle of rotation of the rollers, with a predetermined threshold, to establish the presence or absence of a sheet between the guide members. The sensing means may comprise a core (14), moving with the shaft of one of the rollers, and a solenoid (15) connected to the oscillator circuit.