Document detection device responsive to gas stream pressure changes

Claim 2

Apparatus for detecting a document including a support plate with a smooth document supporting surface; at least one linear slot in the surface of the plate, the slot being aligned in the direction of document feed and being closed at one end and open at the other end; a first orifice adjacent to the closed end of the slot such that the application of pressurised gas to the orifice causes a stream of gas to flow along the slot; a second orifice in the slot intermediate the closed and open ends; a pressure detection means responsive to the gas pressure at the second orifice; and means controlled by said detection means to provide an indication of the presence of a document on the plate and over the second orifice.

Claim 3

Apparatus as claimed in claim 1, wherein one end of each said slot is open at one edge of the plate and is closed at its other end by a cover plate which is recessed into the plate to maintain said smooth supporting surface; and wherein the plate is grooved beneath the cover plate thereby to provide a chamber which abuts the closed end of each said slot and also communicate with a gas inlet tube.

Claim 4

Apparatus as claimed in claim 2, wherein the under surface of the cover plate is grooved in alignment with each of said slots whereby a slit like orifice is formed between the edge of the plate and the bottom of each slot.

Claim 5

Apparatus as claimed in claim 2, wherein the pressure detection means is a pressure responsive transducer in operational communication with the second orifice, and wherein the indication producing means includes a trigger circuit arranged to change its switching state in response to a change in pressure in the slot or slots.

Claim 6

Apparatus as claimed in claim 2 wherein the gas flow in the slot is of such a rate as to exert a force on the document towards the surface of the support plate and thereby provide a frictional restraining force, on the document.

Claim 7

Apparatus as claimed in claim 2, and including a pressure detection means in each said slot, the detection means being arranged along a line transverse to the direction of feeding, the arrangement being such as to generate a group of signals each of such signals serving to indicate when the leading edge of the document has reached the associated detector.

Claim 8

Apparatus as claimed in claim 1, and including a signal coincidence detector to determine whether or not the leading edge of the document is skewed relative to the line of detection means.

Claim 9

Apparatus for detecting the presence of two overlapping documents; including first and second plates each having a smooth document contacting surface disposed to define a guide way for the passage of documents therebetween; means for feeding documents through said guideway; each said plate having on its document contacting surface at least one line or slot aligned with the direction of document feed through the guideway and open at one end and closed at the other end, a first orifice adjacent the slot closed end such that application of pressure gas to the first orifice causes a stream of gas to flow along the slot, and a second orifice intermediate the closed and open eNds; means for producing a gas flow in said slots at such a rate as to exert a force on a document towards the surface of the plate and thereby provide a frictional restraining force on the document; first gas pressure detection means responsive to gas pressure at the second orifice of the first plate; first means controlled by the first gas pressure detection means for producing an indication of the presence of a document at the first plate; second gas pressure detection means responsive to gas pressure at the second orifice of the second plate; second means controlled by the second gas pressure detection means for producing an indication of the presence of a document at the second plate; and means responsive to the simultaneous receipt of a said indication from the first and second gas pressure detection means to indicate the presence of overlapping documents in said guideway.

Claim 10

Apparatus for detecting the presence of two overlapping documents; including first and second plates each having a smooth document contacting surface disposed to define a guide way for the passage of documents therebetween; means for feeding documents through said guideway; each said plate having on its document contacting surface at least one line or slot aligned with the direction of document feed through the guideway and open at one end and closed at the other end, a first orifice adjacent the slot closed end such that application of pressure gas to the first orifice causes a stream of gas to flow along the slot, and a second orifice intermediate the closed and open eNds; means for producing a gas flow in said slots at such a rate as to exert a force on a document towards the surface of the plate and thereby provide a frictional restraining force on the document; first gas pressure detection means responsive to gas pressure at the second orifice of the first plate; first means controlled by the first gas pressure detection means for producing an indication of the presence of a document at the first plate; second gas pressure detection means responsive to gas pressure at the second orifice of the second plate; second means controlled by the second gas pressure detection means for producing an indication of the presence of a document at the second plate; and means responsive to the simultaneous receipt of a said indication from the first and second gas pressure detection means to indicate the presence of overlapping documents in said guideway.