Abstract: A jam detector comprising a sensor for producing a first signal which indicates the presence of a document at a predetermined position in a document path and a second signal which indicates the absence of a document at the predetermined position in the document path. The presence and absence indicating signals are sampled at regular intervals of document motion along the document path and the resultant signals are applied in a preferred embodiment to a bidirectional counter to increment for presence signals and decrement for absence signals. These presence and absence signal indications are accumulated in the counter and a jam indication is produced when the accumulated count reaches a predetermined value.

Abstract: A document stacking table is lowered in steps under electronic control as the documents accumulate. A predetermined number of documents are stacked, after which the table is lowered by a predetermined amount. An optical sensing arrangement is used to determine the effective top of the stack of documents within the limits of "light sensed" and the "absence of light". If light is sensed, the count is increased and the table lowered again; in the absence of light the count is decreased and the table is again lowered. Thus the stacking table will be lowered by a fixed amount to the level of least error.