GB2257510A

GB2257510A - Photodetector chain for document detection in a printer

Info

Publication number: GB2257510A
Application number: GB9212771A
Authority: GB
Inventors: Paavo Perala
Original assignee: ICL Personal Systems Oy
Current assignee: ICL Personal Systems Oy
Priority date: 1991-06-24
Filing date: 1992-06-16
Publication date: 1993-01-13
Anticipated expiration: 2012-06-16
Also published as: JP2872492B2; DE4219547A1; GB9212771D0; JPH05213486A; GB2257510B; ITTO920536A0; ITTO920536A1; DE4219547C2; ES2070033B1; IT1259592B; FI88133B; ES2070033R; FI913077A0; ES2070033A2; FI88133C

Description

1 A printer or a similar output device The present invention relates to a

printer or a similar output device f or producing characters on a document fed into a paper transfer passage of the device, comprising a means provided in connection with the paper transfer passage for detecting the document, said means comprising one or more sources of light and several photodetectors positioned along the paper transfer passage so that the fed document causes a change in the amount of light received by at least one photodetector.

Conventional printers used in banking, for instance, utilize photoelectric components for detecting the presence of a document. Such components can be used in several ways, typically in three different ways. First, it is possible to provide a light source, such as a LED emitting infrared light, at the bottom of the paper transfer passage, and a photo- transistor at a corresponding point on the upper sur face of the paper transfer passage for detecting the light emitted by the LED when no hindrance, i.e. no document, is positioned between the LED and the phototransistor. The second basic principle is to position both the source of light and the photodetector at the bottom of the paper transfer passage, so that the light is caused to propagate between them when a document with a reflective lower surface is brought above them. The third basic principle is to position both the photoemitter and the photodetector similarly as above, i.e. at the bottom of the paper transfer passage, whereas they are continuously connected with each other through a means reflecting the light beam, such as a prism, positioned on the upper surface of the paper transfer passage. In this case, 2 the connection between the photoemitter and the photodetector is broken when a document is fed into the paper transfer passage. The above- described spotlike detectors are typically provided at the edge of the paper transfer passage in the vicinity of an edge guide. When using this kind of printer, the document has to be positioned against the edge guide, and so it suffices that the document detector is positioned in the vicinity of the edge guide. In such a case, the presence of the document in the paper transfer passage can be detected by a single spot-like detector.

To detect whether the document is straight in the paper transfer passage, that is, whether its back edge is at right angles to the longitudinal direction of the paper transfer passage, more advanced structures based on the above-mentioned basic detectors are used, in which two detectors of the type described above are positioned on the same line, which is at right angles to the longitudinal direction of the paper transfer passage. When only one of these detectors indicates that the document is in the paper transfer passage, one knows that the document is not straight. On the contrary, when both detectors detect the presence of the document, one knows that the document is straight. This, of course, requires that the line on which the detectors are positioned is right at a back edge guide for the document. The purpose of the back edge guide is to ensure that the document is straight before it is fed into the paper transfer passage.

In printers where the feeding of the document is allowed practically at any transverse position of the paper transfer passage, that is, it need not be positioned against the side edge guide, the document 1 can, of course, also be detected by using detectors of the type described above, provided that a sufficient number of detectors are positioned on a line extending transversely across the paper transfer passage. A problem therewith is, however, that the signals of several photoemitters and particularly several photodetectors have to be observed simultaneously. Although it is easy to obverse several photodetectors simultaneously, it increases, with conventional solutions, the demand of wiring and complicates the detection equipment itself. These factors also have importance in view of the competitiveness of the product in printers which are intended for mass production and which should also be as small as possible.

The object of the present invention is to provide a printer or a similar output device in which the document can be fed into the paper transfer passage at any point of the passage, while the detection of the document, however, is performed very simply in spite of the use of several photodetectors. A printer or a similar output device by means of which this object can be achieved is characterized in that the photodetectors are connected in sequence into a chain so that a change in the amount of light received by one detector causes a change in a current flowing through the entire chain, the change being detectable by a signal detector connected to the chain.

In cases where it is to be monitored whether the document is at right angles to the paper transfer passage so that the photodetectors have to be positioned in pairs, the printer or a similar output device according to the invention is characterized in that the photodetectors are connected into two 4 chains, one photodetector of each pair of photodetectors being included in one chain and the other photodetector being included in the other chain, respectively, so that a change in the amount of light received by one photodetector causes a change in a current flowing through the entire chain, the change being detectable by a signal detector connected to the chain, and that the output signals of the signal detectors of the chains are connected to a logic means which gives an output signal indicating that the document is at right angles when both of its input signals change.

Preferably, the detection of the document is realized so that a voltage is connected across the chain formed by the photodetectors, and that a change in the current flowing through the chain is detected on the basis of the voltage acting across a resistor connected as a part of the chain.

In the simplest and most reliable embodiment, the signal detector comprises a comparator arranged to compare the voltage acting across the resistor connected to the chain of photodetectors with a reference voltage.

In one preferred embodiment, the photodetector is a phototransistor, the emitter electrode of a preceding phototransistor in the chain being connected to the collector electrode of the next phototransistor in the chain.

put In the following the printer or a similar o u t device according to the invention will be described in greater detail with reference to the attached drawing, in which Figure 1 illustrates one exemplifying way of detecting a document in the paper transfer passage of a printer; :1 Figure 2 illustrates the way according to the invention for interconnecting photodetectors; and Figure 3 illustrates the way according to the invention for interconnecting photodetectors when the photodetectors are arranged to operate in pairs so as to monitor whether the document is at right angles.

Figure 1 is a schematic view of a paper transfer passage 1 of a printer or a similar output device, a document 1 being positioned at an arbitrary point in the paper transfer passage 1. Sources of light Ul, U2, U3... UN are provided on the lower surface of the paper transfer passage, such as LEDs emitting infrared light. In order that the signal sent by the sources of light would be of a beam width as narrow as possible, an optical mask 3 is positioned on the lower surface of the paper transfer passage 1. Photodetectors Q1, Q2,... QN, such as phototransistors, are positioned on the upper surface of the paper transfer passage 1 opposite to the sources of light. In order that the photodetectors would receive only the narrow light beam sent by the photoemitters, an optical mask 3 is also positioned on the upper surface of the paper transfer passage 1 in front of the photodetectors so that the light propagates to the photodetectors through the openings of the optical mask 3. Typically, the light from the photoemitters is not continuous but modulated appropriately so as to eliminate the disturbing effect of the light falling on the photodetectors from the environment as efficiently as possible. The arrangement of the type shown in Figure 1, comprising several spot-like photoemitter/photodetector pairs, could be realized on one of the wellknown principles referred to above.

In the invention, the photodetectors Q1, Q2, Q3 6 .. QN are connected in sequence into a shown in -Figure 2. In the chain, electrode of a preceding phototransistor to the collector electrode of the chain C, as the emitter is connected next photo- transistor in the chain. A resistor R is connected to the end of the chain, and a voltage VCC is connected across the chain C. As all the photodetectors receive light when the document has not yet been fed into the paper transfer passage but the photoemitters are already in operation, a current flows through the chain C, which causes a relatively high voltage loss in the resistor R as the impedances of the photodetectors are thereby relatively low. The voltage across the resistor R is monitored by a signal detector, in the embodiment of Figure 2, by a comparator COMP, which compares the voltage acting across the resistor R with a reference voltage UREF. When the voltage acting across the resistor R exceeds the reference voltage, there is no document in the paper transfer passage. When a document is then fed into the paper transfer passage, at least one of the photodetectors is covered so that its impedance increases substantially. Thus the current flowing through the chain C decreases significantly, as a result of which the voltage acting across the resistor R also decreases. As this voltage drops below the reference voltage UREF, the output of the comparator COMP changes its state, which indicates that there is a document present in the paper trans- fer passage.

The arrangement shown in Figure 2 enables the feeding of the document to be detected very simply and reliably at any point of the paper transfer passage, provided that the distances between the photodetectors are small enough. The distance between 7 0 the photodetectors is determined mainly by the smallest allowable document width. In spite of the use of several photodetectors, the coupling arrangement effecting the detection is very simple when the photodetectors are connected into a chain in accordance with the invention.

Figure 3 shows the coupling arrangement utilizing the way of detection according to the invention when it is to be monitored whether the document is at right angles to the paper transfer passage. In this case, as mentioned above, the detectors are positioned in pairs, and when both detectors in a pair indicate that the document is present, the document is straight. When utiliz---iig the technique according to the invention, the photodetectors are connected into two chains Cl and C2 so that one chain includes one photodetector Q1, Q3, Q5,_,Q(N-1) of each pair of photodetectors and the other chain includes the other photodetector Q2, Q4, Q6,...' QN of each pair of detectors, respectively. The chains Cl and C2 are utilized similarly as in connection with the embodiment of Figure 2 to detect by means of comparators COMP1 and COMP2 whether a document has been fed into the paper transfer passage so that it covers one of the photodetectors. However, it will not indicated that the document is positioned at right angles in the paper transfer passage unless both photodetectors in the pair of photodetectors detect the document, so that it is required in the arrangement shown in Figure 3 that both comparators COMP1 and COMP2 should give a signal indicating the presence of the document before the document is indicated to be positioned at right angles to the paper transfer passage. For this purpose, the outputs of the comparators COMP1 and COMP2 are connected to a logic 8 means, such as an AND means AND, which produces a signal indicating the straight position of the document at its output when both detector chains Cl and C2 have detected the presence of the document.

The principle according to the invention for detecting a document in the paper transfer passage of a printer or a similar device has been described only in connection with an exemplifying embodiment in which the photodetector is a phototransistor. It is, however, to be understood that the coupling principle described above can also be applied in connection with photosensitive components of other types if only their basic operating principles are taken into account in forming the coupling arrangement. It is essential in the invention that the photodetectors are connected in sequence into a chain so that a change in the amount of light received by one photodetector causes a change in the current flowing throughout the chain, and so the presence of the document can be detected reliably on the basis of this change.

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Claims

Claims:

v 1. A printer or a similar output device for producing characters on a document (2) fed into a paper transfer passage (1) of the device, comprising a means provided in connection with the paper transfer passage for detecting the document, said means comprising one or more sources of light (U1, U2, UN) and several photodetectors (Q1, Q2,..., ON) positioned along the paper transfer passage (1) so that the fed document (2) causes a change in the amount of light received by at least one photo detector (Q1, Q2,..., ON), characterized in that the photodetectors (Q1, Q2,..., ON) are con- nected in sequence into a chain (C) so that a change in the. amount of light received by one detector causes a change in a current flowing through the entire chain (C), the change being detectable by a signal detector (COMP) connected to the chain.
2. A printer or a similar output device for producing characters on a document (2) fed into a paper transfer passage (1) of the device, comprising a means provided in connection with the paper transfer passage for detecting if the document is at right angles to the paper transfer passage, said means comprising one or more sources of light (U1, U2,..., UN) and photodetectors (Q1, Q3,..., Q(N-1); Q2, Q4, ON) arranged in pairs on the same line perpendicular to the paper transfer passage, the photodetectors being arranged along the paper transfer passage so that when the document (2) is at right angles to the paper transfer passage, it causes a change in the amount of light received by at least one pair of photodetectors (Q1, Q3,..., Q(N-1); Q2, Q4, ON), c h a r a c t e r i z e d in that the photo- detectors are connected into two chains (Cl, C2), one photodetector (Q1, Q3,..., Q(N1)) of each pair of photodetectors being included in one chain (Cl) and the other photodetector (Q2, Q4,..., QN) being included in the other chain (C2), respectively, so that a change in the amount of light received by one photodetector causes a change in a current flowing through the entire chain, the change being detectable by a signal detector (COMP1, COMP2) connected to the chain (Cl, C2), and that the output signals of the signal detectors (COMP1, COMP2) of the chains are connected to a logic means (AND) which gives an output signal indicating that the document is at right angles when both of its input signals change.
3. A printer or a similar output device accord- ing to claim 1 or 2, characterized in that a voltage (VCC) (C; Cl, C2), and that through the chain is voltage acting across part of the chain.
4. A printer or a similar output device according to claim 3, c h a r a c t e r i z e d in that the signal detector comprises a comparator (COMP; COMP1, COMP2) arranged to compare the voltage acting across the resistor (R) connected to the chain of photodetectors with a reference voltage (UREF).
5. A printer or a similar output device according to anyof claims 1 to 4, characterized in that the photodetector is a phototransistor ((Q1, Q2,..., QN), the emitter electrode of a preceding phototransistor in the chain being connected to the collector electrode of the next phototransistor in the chain.
6. A printer substantially as hereinbefore described with reference to the accompanying drawings.

is connected across the chain a change in the current flowing detected on the basis of the a resistor (R) connected as a l, 1