USRE28660E

USRE28660E - Discriminating apparatus for moving translucent sheets

Info

Publication number: USRE28660E
Authority: US
Inventors: R S Pettet
Original assignee: De la Rue Instruments Ltd
Current assignee: De la Rue Instruments Ltd
Priority date: 1970-06-04
Filing date: 1973-09-17
Publication date: 1975-12-23

Abstract

Apparatus for discriminating between moving translucent sheets comprising a sheet transportation means adapted to convey the sheets in spaced relationship along a flow-line, a photoelectric detection device sited on one side of the flow-line, a first differential amplifier having an input in circuit with the said detection device and adapted to produce a first output signal every time the photoelectric device detects attenuation of the light source in excess of a first predetermined value, and a second differential amplifier having an input also in circuit with the said detection device and adapted to produce a second output signal every time the photelectric device detects attenuation of the light source in excess of a second different predetermined value.

Description

United States Patent 1191 Pettet 145] Reissued Dec. 23, 1975 1 DISCRIMINATING APPARATUS FOR 3,520,404 7/1970 Pine 209/1117 MOVING TRANSLUCENT SHEETS 3,525,433 8/1970 Babb 209/1 1 117 3,578,315 5/1971 Milford 271/263 Inventor! Ronald Sidney Pettel, Portsmouth, 3,611,887 10/1971 Shibanuma 93/93 c England [73] Assignee: De La Rue Instruments Primary Examiner Ev0n C Bhmk [22] Filed: Sept. 17, 1973 [21] Appl. No.: 397,622

Related US. Patent Documents Reissue of:

[64] Patent No.: 3,731,916

Issued: May 8, 1973 Appl. No; 148,744 Filed: June 1, 1971 [30] Foreign Application Priority Data June 4, 1970 United Kingdom 26,940/70 [52] US. Cl. 271/263; 250/559; 250/560; 271/64 [51] Int. Cl. B6511 7/14 [58] Field of Search 271/263, 262, 258, 64; 209/1l1.7; 250/559, 560, 360; 93/93 C [56] References Cited UNITED STATES PATENTS 3,186,708 6/1965 Hinz 271/263 Limited, London, England Assistant ExaminerBruce H. Stoner, Jr. Attorney, Agent, or FirmBaldwin, Wight & Brown 57 ABSTRACT Apparatus for discriminating between moving translucent sheets comprising a sheet transportation means adapted to convey the sheets in spaced relationship along a flow-line, a photoelectric detection device sited on one side of the flow-line, a first differential amplifier having an input in circuit with the said de tection device and adapted to produce a first output signal every time the photoelectric device detects attenuation of the light source in excess of a first predetermined value, and a second differential amplifier having an input also in circuit with the said detection device and adapted to produce a second output signal every time the photelectric device detects attenuation of the light source in excess of a second different predetermined value.

17 Claims, 5 Drawing Figures Reissued Dec. 23, 1975 Sheet 1 of 3 R6. 28,660

Reissued Dec. 23, 1975 Sheet 2 of3 Re. 28,660

OUTPUT F02 A L m/c/eussszs.

OUTPUT F0 M096 7764 ONE THICKNESS.

PULSE COUN TER GATE T T ER N NSN W was 7 a w Np U5 IN m W m r M n m C H s w W ow 7 Reissued Dec. 23, 1975 shw 3 Ora Re. 28,660

INHIBIT II G. 4-

DISCRIMINATING APPARATUS FOR MOVING TRANSLUCENT SHEETS Matter enclosed in heavy brackets I: 1 appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to apparatus adapted to dis criminate between lengths and thickness of translucent sheet material travelling along a flow-line at high speed and optionally to count some or all of such sheets. More especially, the invention relates to such apparatus which includes a photoelectric detection means and an associated light source disposed on opposite sides of the flow-line in such a manner that the photoelectric means is subjected to variations of light intensity during the passage of the sheets.

BACKGROUND OF THE INVENTION In many sheet feeding machines, for example, in the case of machines adapted to feed and count treasury notes, it is essential that an exact count is recorded of the number of pieces actually delivered. To this end it is usual to provide means which ensure that multiple or superposed notes are not counted as a single unit.

A known method of achieving the above requirement is to feed the notes through a critical gauging throat which may be arranged to hold back superposed notes, or to stop the machine when sheets of abnormal thickness are present, or more preferably to actuate a divertor means which serves to remove multiple notes from the flow-line before they are fed to a counting and delivery stage. An example of the latter arrangement is described in our British Pat. No. 898,7l5 in which the gauging throat comprises a nip of a critical dimension formed between a pair of driven gauging rollers. It is so arranged that normal thickness notes pass through the nip, but multiple or excess thickness-notes cause a displacement of the axis center of one of the rollers which brings into effect a solenoid actuated divertor. Counting is carried out by means of an electrical makeand-break circuit disposed downstream of the divertor which advances a digital counter in an incremental manner. Such an arrangement possesses a finite operating speed because of the mechanical inertia of the detection means and, furthermore, because of the difficulties in differentiating between relatively small differences of thickness at high speed, considerable constructional problems are created. It has been found in practice that the gauging nip must be adjusted within fine limits to promote the desired sensitivity to abnormal thickness and furthermore mechanical wear of certain critical components necessitates careful maintenance to retain the desired degree of reliability.

SUMMARY OF THE INVENTION It is one object of the present invention to provide apparatus for discriminating between sheets of the above-described kinds without the need for a precise mechanical gauging throat.

According to the present invention apparatus for discriminating between moving translucent sheets comprise a sheet transportation means adapted to convey the sheets in spaced relationship along a flow-line, a photoelectric detection device sited on one side of the flow-line and an associated light source sited on the other side of the flow-line, a first differential amplifier having an input in circuit with the said detection device and adapted to produce a first output signal every time the photoelectric device detects attenuation of the light source in excess of a first predetermined value, and a second differential amplifier having an input also in circuit with the said detection device and adapted to produce a second output signal every time the photoelectric device detects attenuation of the light source in excess of a second different predetermined value. Thus in one embodiment of the invention apparatus for handling sheets of a like-kind may be so adapted that the output of the said first differential amplifier controls a first digital counting circuit to record the total quantity of single sheets or groups of adhered-together" sheets fed along the flow-line, and that the output of the said second differential amplifier controls a second digital counting circuit to record solely the number of groups of adhered-together" sheets.

Preferably the apparatus also includes a sheet divertor means disposed downstream of the said detection device and under the control of the said second differential amplifier, the arrangement being such that the divertor, which is normally inoperative, is moved to an operative position every time the said second output signal is created. In a specific embodiment it may be arranged for a count pulse to be inhibited from the said first counting circuit every time the divertor is moved to the operative position thereby to record only the passage of single sheets.

Preferably the apparatus also includes a pulse-counter unit fed from a pulse generator via a gate under the control of the output of the first differential amplifier, said unit being capable of ascertaining the length of a sheet or the overall length of overlapping sheets in the direction of the flow-line thereby, in conjunction with the output of the second differential amplifier, to detect the presence of superposed, partially overlapping or edge-abutting sheets.

Preferably the said pulse generator is driven in unison with the linear travel of the sheets in the flowline. In a convenient form the pulse generator comprises a circumferentially perforated or notched wheel member positively driven by the drive mechanism of the said sheet transportation means, and adapted to influence a transducer which may be of the optical or magnetic kind.

One embodiment of the invention will now be described with reference to the accompanying drawings of which:

FIG. I is a side elevation of a banknote feeding and transportation mechanism showing the basic parts thereof;

FIG. 1a is a fragmentary end view of some of the parts of the mechanism of FIG. 1;

FIG. 2 is a diagram of part of an electrical circuit for performing the optically discriminating aspect of the invention; I: and 1 FIG. 3 is a schematic block plan showing the interconnection of various electronic assemblies useful in the performance of the invention and FIG. 4 is another block plan showing the interconnection ofdigital counters operative by the electrical circuit of FIG. 2.

In FIG. 1, the banknote feeding, transporting and deflecting mechanisms are substantially similar to those disclosed in our British Pat. No. 893,715 and comprise essentially an inclined stack support member 1 adapted to support a stack of banknotes N on edge. The notes are biassed (by means not shown) towards an oscilla- Lory suction arm 2 provided with an angled suction port 3 which contacts the lower central face of the frontnost note in the stack and feeds it into the nip ofa pair 3f

primary feed rollers

4 and 5. The lower roller 5 is )rovided with a cut-away portion 6 to facilitate entry of :he leading side edge of the note. The arm is oscillated )y means of a tubular shaft member 7 which is adapted .o be moved in a bi-rotational manner by a cam system iriven in unison with the

primary feed rollers

4 and 5;

.he interior of the shaft 7 is in communication with a lOUICC of suction (not shown). When the circumferen- .ial surfaces of the feed rollers co-act, the note is pulled rom the face of the suction port 3, and is passed be- .ween a light L1 and an associated photoelectric de- .ector PET, and thence into the nips of three pairs of :onveying rollers 8,9; 10,1]; and 12,13 respectively. The nips of the primary and conveying rollers collecively define a substantially linear flow-line for the iotes which terminates at the arrow 14; delivery means )eyond the arrow form no part of the present inven- .ion.

A note divertor means provided between the conveyng rollers 10,11 and l2, 13 comprises a plurality of spaced fork members [5 rigidly attached to a shaft 16 vhich also includes an actuating lever 17 connected to .he slidable armature 18 of a solenoid l9 by means of 1 connecting link 20. The divertor assembly is biassed .0 an inoperative position, as shown by means of a .ension spring 21. An auxiliary rubber-surfaced driven 'oller 22 is provided above the upper conveying roller l0, and a *reject note hopper 23 is provided above be

rollers

4 and 8 to receive diverted notes. Energizavion of solenoid 19 causes the divertor assembly to nove to the position indicated by the chain-dotted line, whereupon the tips of the fork members descend nto the flow-line thereby to cause a note or notes to be Jropelled around 180 of the circumference of the 'oller l0 and thence into the hopper 23.

To facilitate the passage of notes through the roller iystem a series of parallel guide members, one of which s indicated by symbol 24, are provided below the flowme.

The entire roller system is driven at a constant peipheral speed through a gear train generally indicated it 25, by an electric motor 26 via a two-stage gear 'eduction disposed on secondary shafts 27 and 28. The ihaft 27 (see also FIG. la) mounts a fixedly attached :lisc member 29 which is provided with an equally )itched circumferential row of holes 30. A light source L2 and an assocated photoelectric detector PEZ are jisposed in alignment with the holes 30 on the opposite ;ides of the disc.

The electronic circuitry of the apparatus will now be iescribed with reference to FIGS. 2 and 3. it should be ioted that the two outputs x and y of HG. 2 are coniected respectively to the left-hand side of FIG. 3.

The output of the photoelectric detector PE! is fed nto a linear amplifier the output of which feeds into :wo substantially similar networks, and thence through 'espective differential amplifiers to points x and y. The assembly 1 serves to provide an output signal at x for :ach single note or group of partially or wholly supernosed notes that pass between L] and PEI, and the assembly ll (which is of course pre-set in a different manner), serves to provide an output signal at y for 4 each multiple thickness note or notes, or each single note having an abnormally high opacity that passes between L1 and PEl.

The output of the linear amplifier 50 passes through a rectifier MR which, with a capacitor C1, forms a peak level detection means. When no note is interposed between L1 and PE] the linear amplifier produces a peak output proportional to the intensity of the light falling on the photoelectric detector PB]. The rectifier MR permits only the positive peak to charge the capacitor Cl and effectively prevents reverse flow of current from C1 when the light falling upon PE] is attenuated by the presence of a note.

An R/C network comprising C1, R1, RVl and R2 provides a time-constant sufficiently long to prevent any significant discharge ofCl during the period when light is attenuated. The arrangement is self-compensating insofar that a gradual fall-off of light output created by the ageing effect of the light source, a deterioration in the sensitivity of the photoelectric detector or a reduction of gain of the linear amplifier, is compensated for automatically because the charge of Cl will also reduce at the same rate.

Having charged the peak level detection means up to the voltage produced by the unattenuated light source, a proportion of it is coupled to the inverting input of the differential amplifier via the slider of the potentiometer RV 1. The potentiometer thus provides a presetting means for adjusting the sensitivity of the assembly. The full output of the linear amplifier, taken from a point upstream of the rectifier MR, is connected to the positive non-inverting" input of the differential amplifier. Hence, when the light falling upon the photoelectric detector is unattenuated the voltage to the non inverting" input provides positive feed-back so that the output it of the differential amplifier will be a maximum positive. Conversely. when the light level is attenuated, the output of the linear amplifier will fall to below the level set on the inverting" input with the result that the differential input will be "inverted" thereby to produce a negative output it from the differential amplifier. A positive feed-back loop comprising the resistor R4 ensures that the output x will be a maximum negative.

The assembly II, which terminates at an output y, is substantially similar to that described above and serves to produce an output pulse of changed polarity when the light is attenuated to a greater degree, for example on the passage of a plurality of adhered-together notes.

The means for discriminating between the length of a single sheet and the overall length of superposed sheets, as measured in the direction of the flow-line. will now be described.

Operation of the roller system of the machine also causes, through the medium of the gearing system, the perforated disc member 29 to rotate, with the result that a succession of electrical pulses is created in the photoelectric detector PE2. These pulses are fed into a Pulse Counter via a Latched Gate" (see FIG. 3) which is opened at the commencement of every period of attenuation of PEI, via the electronic assembly 1 and closed after a preset number of pulses have been fed into the Pulse Counter". The number of pulses fed into the Pulse Counter" is directly proportional to the angular displacement of the shafts in the drive mechanism, and hence to the length of the sheet being fed.

The Pulse Counter" provides outputs in accordance with three different preset and ascending numbers of datum counts which permit decisions to be effected in accordance with the overall length of a sheet or sheets passing through the optical system. These counts are routed in the following manner:

COUNT A into a Divert Command Generator" which also receives signals from the electronic assembly II via connection y. The Divert Command Generator" is provided with two alternative outputs viz, a YES output to the divertor solenoid l9 and a Count Pulse Generator", or a NO output to a Warning Generator".

If signals from connections y are received before COUNT A is reached, the YES output is obtained, the divertor solenoid 19 is actuated and an INHIBIT signal is fed to the COUNT PULSE GENERATOR. If COUNT A is exceeded before signals are received from the connection y, the NO- output is energized and the WARNING GENERATOR is energized.

COUNT B into the Warning Generator" (which also receives signals from the x connection during the entire period of the attenuation of the light of LI) and thence to a warning device shown diagrammatically at symbol SI. COUNT C into the Count Pulse Generator (which, as mentioned above, also receives INHIBIT signals when the divertor is actuated) and thence into a digital counter and display unit shown diagrammatically at symbol 52. In addition a RE-SET pulse is fed back to unlatch the LATCHED GATE upon attainment of COUNT C. Actuation of the Apparatus, including examples of correct and incorrect note feeding.

Energization of the driving motor 26 will cause banknotes to be fed sequentially from the front of the stack N into the roller system along the flow-line thereby to attenuate in an intermittent manner the light falling upon the photoelectric detector PEI. Pulses will also be generated by the photoelectric detector PE2 through rotation of the disc member 29.

Case I The passage of a normal length single note will record a counting pulse in the counter unit 52 in the following manner:

When the leading edge of the note attenuates the light source a signal from the all-thickness" assembly I opens the Gate which allows pulses from PE2 to pass into the Pulse Counter. For a note of normal length, the light attenuation signal from x into the WARN- ING GENERATOR" terminates before COUNT B is reached and thus no warning is generated. When the Pulse Counter" reaches COUNT C" a count pulse is generated and a count of one is registered in the counter unit 52.

Case 2 The passage of two superposed or substantially superposed notes will be rejected in the following manner:

In a manner similar to that described in (1) above, the Gate passes pulses to the Pulse Counter" but in this case, a multiple-thickness pulse is generated by the assembly II through the connection y and Divert Command Generator. If the y signal, which is indicative of the commencement of the multiple thickness during the passage of the sheets, is created before COUNT A is reached the sheets are capable of diversion and accordingly the Divert Command Generator generates a YES signal and energizes the solenoid 19 of the divertor thereby to cause the superposed notes to be com veycd into the reject note hopper 23. At the same time the count pulse at COUNT C" is inhibited and no count is recorded in the counter unit 52. If signal y is created after COUNT A is reached, diversion is not possible and the superposed or substantially superposed sheets are treated as partially overlapping sheets (see Case 3 below).

Case 3 The passage of two partially-overlapping notes will be handled in the following manner:

The cycle of operation is initiated as in Case 2 above but in this case COUNT A is reached before the creation of the y signal and the Divert Command Generator does not energize the solenoid 19 of the divertor. This prevents the mechanism from attempting to divert a note, the leading edge of which has already passed below the tips of the divertor fork members 15. Instead, a NO signal is applied to the Warning Gener ator" which give a warning signal and the count pulse is not inhibited.

Case 4 The passage of two edge-abutting notes (viz. with no overlap) is handled as follows:

The cycle of operation is initiated as in Case 3 above, but in this case no multiple-thickness is detected. However, when COUNT B is reached the output of the all-thickness assembly I at connection x into the WARNING GENERATOR is still maintained thus indicating the presence of an abnormally long article. The Warning Generator" initiates a warning and the Count Pulse Generator is activated as in Case 3.

It will be appreciated that the above described apparatus is capable of counting and discriminating translucent sheets at a very high speed, the upper limit of which is dependent only upon the mechanical limitations of the feeding mechanism. Furthermore, the photoelectric detection means and associated circuitry is self-compensating and thus after an initial setting-up, is capable of operating for long periods without attention.

It will further be appreciated that the complete elimination of the need for a critical gauging throat to detect multiple-thicknesses has simplified the mechanical construction of machines of this general type and avoided the need for frequent adjustment and maintenance.

Reference is now made to FIG. 4 wherein a counter circuitry is shown including afirst digital counter 53 and a second digital counter 54. y signals pass into the second digitalcounter 54 to advance the same one increment for each production ofa y signal. x signals pass through the first digital counter 53 to normally advance the same one increment for each production of an x signal. However, the circuitry includes means for producing an IN- HIBIT signal upon each generation of a y signal to prevent the first digital counter 53 for advancing an increment when both x and y signals are generated.

What we claim is:

1. Apparatus for discriminating between moving translucent sheets comprising a sheet transportation means for conveying the sheets in spaced relationship along a flow-line, a single photoelectric detection device positioned on one side of the flow-line and an associated light source positioned on the other side of the flow-line, a first differential amplifier means for producing a first output signal every time the photoclectric detection device detects attenuation of the light source in excess of a first predetermined value and iaving an input in circuit with the said detection device. and a second differcntial amplifier means for reducing a second output signal every time the photo- :lcctric detection device detects attenuation of the ight source in excess of a second different predeter' nincd value greater than said first predetermined value ind having an input also in circuit with the said detecion device and means for receiving and utilizing said iutput signals to discriminate between sheets which proiuce solely saidfirst output signal and sheets which proluce both said first and second output signals.

2. Apparatus as claimed in claim I in which the first )utput signal serves to indicate the passage of (a) each .ingle sheet having an opacity greater than the first redetermined value and less than the second predeter nined value; (h) each folded single such sheet; (c) :ach single sheet having an opacity greater than the second predetermined value; and ((1) each group of )artially or wholly superposed single sheets having an pacity greater than the second predetermined value. ind the second output signal serves to indicate the )assage of any sheet in category (b), (c) or (d).

I: 3. Apparatus as claimed in claim I together with neans for coupling the first output signal to a first ligital counter for actuating the same and means for :oupling the second output signal to a second digital :ounter for actuating the same] [4. Apparatus as claimed in claim 3 together with neans for inhibiting the first output signal to the first iigital counter upon the production of the second out- Jut signal. I

5. Apparatus as claimed in claim 1 in which said neans for receiving and utilizing said output signals ncludes a sheet divertor [is provided in the flowine at a point downstream of the photoelectric detec- .ion device, said divertor being normally inoperative with respect to the sheets, but being operable to move nto the flow-line every time the said second output iignal is produced.

6. Apparatus as claimed in claim 5 in which said neans for receiving and utilizing said output signals additionally] includes length discrimination means "or inhibiting actuation of the sheet divertor if the ength of a sheet, or the overall length of a group of Jartially or wholly superposed sheets in the direction along the flow-line, exceeds a predetermined dimension.

7. Apparatus as claimed in claim [6 in I which I: the said said means for receiving and utilizing said )utput signals includes a digital counter and length discrimination discriminator means [comprises 1 'ncluding [a pulse generator driven in unison with the sheet transportation 1 pulse-generating means, a pulse- :ounting means [,1 and gate-switching means [for directing arranged to be opened by said first output signal and to direct a train of pulses from the pulse gen erator to the pulse-counting means whilst a sheet is present between the light source and the photoelectric detection device, and a count-discriminator for activating the sheet divertor only if less than a predetermined number of pulses are directed into]; the pulse-count ing means being operable to produce successively a first sheeelength-indicative datum count, (1 second sheetlength-indicative datum count and a digital count pulse for advancing said digital counter by one increment.

8. Apparatus as claimed in claim 7 in which the said pulse generator comprises a circumferentially perforated wheel positively driven by the sheet transportation means, a second light source disposed on one side of the wheel in alignment with the said perforations, a second photoelectric-detection means disposed on the other side ofthe wheel in alignment with the said perforations and operable upon rotation ofthc wheel to feed a train of pulses into the said gateswitching means.

9. Apparatus as claimed in claim [5] 7 so constructed that the [creation termination of said first output signal and the termination thereof] before the attainment of the second datum count [and the creation of the said second output signal before the attainment of the first datum count] indicates the passage of one or more sheets having an over-all length within a predetermined range of lengths plurality of overlapping sheets and further adapted to cause said divertor to move into the flow-line upon the passage of such sheets].

10. Apparatus as claimed in claim [5] 7 so can structed that the [creation termination of [the said first output signal [and the termination thereof 1 after the attainment of the second datum count [and the creation ofthe second output signal after the attainment of the first datum count indicates the passage of I: a plurality of overlapping sheets, and further adapted to inhibit the movement of said divertor into the flowline and to actuate a warning means one or more sheets having an overall length in excess ofa predetermined length.

ll. Apparatus as claimed in claim 1 in which each differential amplifier means is provided with manually adjustable means adapted to permit the initial setting up of its output level.

12. Apparatus as claimed in claim 11 in which said input to said differential amplifier means includes one input dependent upon the effect of attenuated light upon said photo-electric device and a second input dependent upon the effect of direct light upon said photoelectric device, said second input including said adjustable means.

I: 13. Apparatus as claimed in claim I which additionally includes length discriminator means including a pulse generator driven in unison with the sheet transportation means, a pulse-counting means, gate switching means for directing a train of pulses to the pulsecounting means during production of said first output signal, the pulse counter being operable to produce successive first and second sheet length-indicative datum counts] 14. Apparatus as claimed in claim 13 so constructed that the creation of the first output signal and the termination thereof after the attainment of the first datum count. but before the attainment of the second datum count, indicates the passage of a sheet of predetermined opacity and length] [15. Apparatus as claimed in claim 13 so constructed that the creation of the first output signal and the termination thereof after the attainment of the second datum count indicates the passage of at least one sheet having an overall length in excess of a predetermined length. I

[16. Apparatus as claimed in claim 15 including warning means operable upon the passage of one or more sheets having an overall length in excess of a predetermined length. I

[17. Apparatus as claimed in claim 13 in which the said pulse generator comprises a circumferentially perforated wheel positively driven by the sheet transportation means. a light source disposed on one side of the wheel in alignment with the said perforations, a photoelectric detection means disposed on the other side of the wheel in alignment with the said perforations and adapted upon rotation of the wheel to feed a train of pulses into the said gate-switching means] 18. Apparatus as claimed in claim 9 which additionally includes a sheet divertor in the flow-line downstream of the photo-electric detection device, said divertor being normally inoperative with respect to the sheets but being available to move into theflow-line everytime the second output signal is produced, and a count-pulse inhibit switch means operable in unison with every said divertor movement to prevent said digital count pulse from ad vancing said digital counter by one increment.

19. Apparatus as claimed in claim 10 additionally including a warning means operable on the passage of one or more sheets having an overall length in excess of the predetermined length.

20. Apparatus as claimed in claim 19 additionally including a sheet divertor in the flow-line downstream of the photoelectric detection device, said divertor being normally inoperative with respect to the sheets but being operable to move into the flow-line upon the production of the second output signal as a consequence of the passage ofa sheet or sheets having an overall length within a predetermined range of lengths LII 21. Apparatus as claimed in claim 20 additionally including a count-pulse inhibit means operable in unison with every said divertor movement to prevent said digital count pulse from advancing said digital counter by one increment.

22. Apparatus as claimed in claim 2] additionally including means operable to maintain said divertor in its normal inoperative position upon the production of the second output signal as a consequence of the passage of one or more sheets having an overall length greater than any length within a predetermined range of lengths.

23. Apparatus as claimed in claim I wherein said means for receiving and utilizing said output signals includes a first digital counter coupled to said first differential amplifier means for receiving said first output signal therefrom and to be actuated thereby, and a second digital counter coupled to said second differential amplifier means for receiving said second output signal therefrom and to be actuated thereby.

24. Apparatus as claimed in claim 23 wherein saidfirst digital counter is coupled to said second differential amplifier means for inhibiting a first output signal to said first digital counter upon the production of a second output signal.

Claims

1. Apparatus for discriminating between moving translucent sheets comprising a sheet transportation means for conveying the sheets in spaced relationship along a flow-line, a single photoelectric detection device positioned on one side of the flow-line and an associated light source positioned on the other side of the flow-line, a first differential amplifier means for producing a first output signal every time the photoelectric detection device detects attenuation of the light source in excess of a first predetermined value and having an input in circuit with the said detection device, and a second differential amplifier means for producing a second output signal every time the photoelectric detection device detects attenuation of the light source in excess of a second different predetermined value greater than said first predetermined value and having an input also in circuit with the said detection device and means for receiving and utilizing said output signals to discriminate between sheets which produce solely said first output signal and sheets which produce both said first and second output signals .

2. Apparatus as claimed in claim 1 in which the first output signal serves to indicate the passage of (a) each single sheet having an opacity greater than the first predetermined value and less than the second predetermined value; (b) each folded single such sheet; (c) each single sheet having an opacity greater than the second predetermined value; and (d) each group of partially or wholly superposed single sheets having an opacity greater than the second predetermined value, and the second output signal serves to indicate the passage of any sheet in category (b), (c) or (d).

5. Apparatus as claimed in claim 1 in which said means for receiving and utilizing said output signals includes a sheet divertor (is) provided in the flow-line at a point downstream of the photoelectric detection device, said divertor being normally inoperative with respect to the sheets, but being operable to move into the flow-line every time the said second output signal is produced.

6. Apparatus as claimed in claim 5 in which said means for receiving and utilizing said output signals (additionally) includes length discrimination means for inhibiting actuation of the sheet divertor if the length of a sheet, or the overall length of a group of partially or wholly superposed sheets in the direction along the flow-line, exceeds a predetermined dimension.

7. Apparatus as claimed in claim (6 in) 1 which (the said) said means for receiving and utilizing said output signals includes a digital counter and length (discrimination) discriminator means (comprises) including (a pulse generator driven in unison with the sheet transportation) pulse-generating means, a pulse-counting means (,) and gate-switching means (for directing) arranged to be opened by said first output signal and to direct a train of pulses from the pulse generator to the pulse-counting means (whilst a sheet is present between the light source and the photoelectric detection device, and a count-discriminator for activating the sheet divertor only if less than a predetermined number of pulses are directed into) ; the pulse-counting means being operable to produce successively a first sheet-length-indicative datum count, a second sheet-length-indicative datum count and a digital count pulse for advancing said digital counter by one increment .

8. Apparatus as claimed in claim 7 in which the said pulse generator comprises a circumferentially perforated wheel positively driven by the sheet transportation means, a second light source disposed on one side of the wheel in alignment with the said perforations, a second photoelectric-detection means disposed on the other side of the wheel in alignment with the said perforations and operable upon rotation of the wheel to feed a train of pulses into the said gate-switching means.

9. Apparatus as claimed in claim (5) 7 so constructed that the (creation) termination of said first output signal (, and the termination thereof) before the attainment of the second datum count (and the creation of the said second output signal before the attainment of the first datum count) indicates the passage of one or more sheets having an over-all length within a predetermined range of lengths (plurality of overlapping sheets and further adapted to cause said divertor to move into the flow-line upon the passage of such sheets) .

10. Apparatus as claimed in claim (5) 7 so constructed that the (creation) termination of (the) said first output signal (and the termination thereof) after the attainment of the second datum count (and the creation of the second output signal after the attainment of the first datum count) indicates the passage of (a plurality of overlapping sheets, and further adapted to inhibit the movement of said divertor into the flow-line and to actuate a warning means) one or more sheets having an overall length in excess of a predetermined length.

11. Apparatus as claimed in claim 1 in which each differential amplifier means is provided with manually adjustable means adapted to permit the initial setting up of its output level.

18. Apparatus as claimed in claim 9 which additionally includes a sheet divertor in the flow-line downstream of the photo-electric detection device, said divertor being normally inoperative with respect to the sheets but being available to move into the flow-line everytime the second output signal is produced, and a count-pulse inhibit switch means operable in unison with every said divertor movement to prevent said digital count pulse from advancing said digital counter by one increment.

20. Apparatus as claimed in claim 19 additionally including a sheet divertor in the flow-line downstream of the photoelectric detection device, said divertor being normally inoperative with respect to the sheets but being operable to move into the flow-line upon the production of the second output signal as a consequence of the passage of a sheet or sheets having an overall length within a predetermined range of lengths

21. Apparatus as claimed in claim 20 additionally including a count-pulse inhibit means operable in unison with every said divertor movement to prevent said digital count pulse from advancing said digital counter by one increment.

22. Apparatus as claimed in claim 21 additionally including means operable to maintain said divertor in its normal inoperative position upon the production of the second output signal as a consequence of the passage of one or more sheets having an overall length greater than any length within a predetermined range of lengths.

23. Apparatus as claimed in claim 1 wherein said means for receiving and utilizing said output signals includes a first digital counter coupled to said first differential amplifier means for receiving said first output signal therefrom and to be actuated thereby, and a second digital counter coupled to said second differential amplifier means for receiving said second output signal therefrom and to be actuaTed thereby.

24. Apparatus as claimed in claim 23 wherein said first digital counter is coupled to said second differential amplifier means for inhibiting a first output signal to said first digital counter upon the production of a second output signal.