JPS61105484A - Method and device for monitoring passage of sheet - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for monitoring the passage of paper sheets through at least one sheet detection assembly of a paper feeder, each detection assembly comprising: Generates an output signal whose level changes depending on the nature of the paper sheet.

[Prior art and problems to be solved by the invention]

A typical method for each detection assembly is to set a single sheet output signal threshold to a level exceeded by the output signal generated by the detection assembly as the sheet passes through the detection assembly, and at least It consists of monitoring said output signal when said threshold value is exceeded. Such a method will be explained below.

An example of the method described above is disclosed in International Patent Application Publication No. WO
-A-82101698. In this arrangement, the expected thickness of the banknote is preset and an appropriate signal is applied to the automatic reference path. The automatic reference circuit adds to the expected thickness a value representing data corresponding to the roller located on the guide surface. As a result, when the banknote passes under the roller which is connected through the arm to the linear variable differential transformer, an output signal is sent to the comparator.

The comparator determines whether a bill is present.

Between the passage of each banknote, the data level is rechecked and
An automatic reference circuit makes appropriate modifications to the reference signal sent to the comparator.

One of the problems with these conventional methods is that, for example, for counting purposes, bundles of sheets of paper with different thicknesses, 9 or 9, the sheets in each bundle have about 11 the same thickness, but When attempting to pass a stack of sheets whose thickness differs from that of other sheets, the operator must recalculate the expected signal level to be exceeded when detecting one sheet. This is something that needs to be set.

In the first form of the present invention, the method of class tII is arranged such that the data output signal level is spaced by a predetermined amount from the data output signal level that operates when no paper sheet is detected. In presetting a first threshold, the predetermined amount is determined such that the first threshold is not exceeded as a result of random noise changes in the output signal to be monitored passing through the detection assembly. The output signal is set to be exceeded during the passage of every sheet of paper that passes the data level; In a second aspect of the present invention, at least An apparatus is provided for monitoring the passage of paper past a detection assembly. The detection assembly produces an output signal whose level varies depending on the nature of the paper industry. The device for monitoring is 1. A storage device for storing a single sheet output signal threshold for each sensing assembly, the threshold being exceeded by an output signal generated by the sensing assembly as a sheet passes through the sensing assembly. a storage device corresponding to a signal level such as; a monitoring device for monitoring the output signal; and a means for storing a first preset threshold; The preset threshold value is a predetermined amount apart from the data output signal level when no paper sheet is detected, and the predetermined amount is such that the first threshold value is within the output signal level. The monitoring means is such that the output signal is not exceeded as a result of random noise variations, but is exceeded when all of the sheets to be monitored pass through the detection assembly. means for storing the first preset threshold, the first preset threshold being used to monitor the size of the output signal relative to the data level when passing the threshold; the monitored size; calculating means for calculating a single sheet threshold value from the threshold value and storing the single sheet threshold value in the storage means.

A significant improvement is obtained by presetting the first threshold. In other words, bundles of sheets having different characteristics such as thickness can be automatically processed without the operator having to manually pre-set a single sheet threshold for each bundle.

In the present invention, the first sheet of the stack fed through the sheet feeder is used to set the single sheet threshold. A further important advantage is that by maintaining the first threshold it is possible to detect the passage of a sheet such that the output signal from the detection means does not exceed said single sheet threshold. It is.

This was not possible with conventional configurations. In conventional arrangements, the passage of such sheets was simply ignored, causing an erroneous +tl count in the counting device.

The key point in this system is that if the first sheet fed is imprecisely fed, such as two sheets stuck together, the single sheet threshold generated will also be This is because it is inaccurate. However, this is detected when the next sheet is fed. The reason is that the single sheet threshold is not exceeded by the output signal from the detection means. In such a situation, the method may further preferably generate an error signal if the output signal exceeds the first threshold but not the single sheet threshold. The error signal may, for example, cause the paper feeder to stop so that the operator can retrieve the incorrectly fed paper.

Typically, the threshold is a positive value, such as a voltage level that is exceeded by the output signal when a sheet of paper passes the detection means.

In a bundle of sheets each having the same properties, there will typically be slight variations in those properties. Preferably, therefore, the single sheet threshold is generated as a ratio of the output signal produced by the detection means when a sheet passes through the detection means.

- As an example, the single sheet threshold is set at 0.625 VC of the monitored output signal.

The method has special application to counting paper sheets. In the simplest example, each time the single sheet threshold is exceeded, the count is incremented by one. The method can be used to cause a paper feeder to feed a specified amount of bundles of sheets and to stop the paper feeder when a certain number is reached. Alternatively, it can be used to simply count the total number of sheets in a bundle.

After all the sheets in the stack have been fed through the paper feeder, the method further calculates all the thresholds (
(except for the first threshold value set in advance). In this way, the method can repeat the processing of further bundles of sheets with different characteristic values using the preset first threshold.

Preferably, the method further comprises generating a double sheet threshold from the monitored size, the level of the output signal from the detection assembly during the passage of two or more overlapping sheets. exceeds the double sheet threshold.

This allows the detection of overlapping sheets and, if these overlapping sheets are unacceptable, generates an error signal, for example stopping the sheet feeding device.

In a more precise arrangement, the device may further consist of generating a triple sheet threshold from the monitored size;
During the passage of one or more sheets, the output signal level from the detection assembly exceeds the triple sheet threshold. This provides particular advantages when used in conjunction with double leaf threshold generation. If the double form threshold is exceeded but the triple form threshold is not,
In some situations, it is assumed that two sheets of paper have been fed, and this may be acceptable. If the count is rising, the count will be incremented by two. However, if the triple leaf threshold is exceeded, an error signal is preferably generated.

Here, "overlapping" means that the paper sheets completely overlap or partially overlap. In either case, at some stage during the passage of the overlapping sheets, at least the double sheet threshold is exceeded.

Preferably, the output signal of each detection assembly changes depending on the thickness of the sheet. Alternatively, other characteristics such as leaf length and opacity can be monitored. In a particularly advantageous arrangement, both the thickness and length of the sheet are monitored.

As used herein, "length" means the dimension of a sheet in the direction of movement.

For example, if a sheet passes through each detection assembly at a substantially constant speed, monitoring the length consists of monitoring the time during which a single sheet threshold is exceeded. Alternatively, the length can be determined by monitoring the output of the timing disk.

When monitoring length, the method comprises generating an error signal if the length of the monitored sheet differs significantly from the monitored length of the first supplied sheet passing through the detection assembly. can.

The method comprises spaced apart two sensing assemblies across a sheet feeding path and monitoring the output signal from each sensing assembly to detect passage of an incorrectly fed sheet. This is desirable. The use of two detection assemblies allows the detection of the passage of obliquely fed filter paper sheets, folded paper sheets, etc.

Each detection assembly can be made of any conventional detection system that provides an output signal that varies depending on some characteristic of the applied filter paper sheet. Preferably, however, each detection assembly consists of a set of guide surfaces defining a gap through which the sheet passes and means for detecting deviations of one guide surface relative to the other. This allows seven digits of sheet thickness to pass through the detection assembly.

An example of a particular suitable detection assembly is described in related Japanese Patent Application No. 59-133488. In this arrangement, the configuration of the guide surfaces when no sheet is fed through the gap between the guide surfaces is generated and stored. The form of this guide surface corresponds to the data level of the invention.

The method and apparatus have particular application in banknote feeding devices, such as banknote counting and storage devices.

〔Example〕

An example of a banknote counting device for carrying out the method according to the invention is described below with reference to the accompanying drawings. The illustrated device is a banknote counting device.

This device consists of a metal storage box 1 that supports an input hopper 40, a base plate 2, and an end plate 3. Two conventional picker wheels 5 are rotatably installed in the storage box IK and have bosses 6 that project radially outward. The posts 6 periodically project through the slots in the pace plate 2 as the picker wheel 5 rotates.

A guide plate 7 with a curved guide surface 8 is pivotably mounted on a projection 9 attached to the end plate 3 by an arm 7'. two separation rollers 10
(only one shown in the figure) are rotatably mounted on the shaft 11. The cantilever arm 12 is connected to the guide plate 7 and includes a spring clip 13. When the guide plate 7 is in the first position shown, the spring clip 13 is located around the fixed shaft 14 VC. If you wish to pivot the guide plate 7 away from the first position, simply remove the clip 13 from the shaft 14 and
A counterclockwise rotation (K as shown in FIG. 1) allows the operator access to the bill supply path and remove the bill jam.

A set of drive rolls 15 is non-rotatably mounted on a drive shaft 16, which in turn is rotatably mounted on storage box 1. Each drive roll 15 has an outer annular portion 17 made of rubber.

Each drive roll 15 contacts a respective auxiliary roll 18 rotatably attached to the shirt 14.

One set of stripping salt rollers 19 is attached to the shirt so that it can be rotated by 20KDO. The shirt 20 is located around the shaft 16 and has a larger diameter than the shaft 16.

The shaft 20 is fixed between the arms 21 of the cradle 2201 set. Cradle 22 is rotatably attached to auxiliary drive shaft 23. Auxiliary drive shaft 2
A picker wheel 5 is installed on top of the picker wheel 3. The cradle 22 has a cam part 24, and the cam part 24 is connected to a cam 25 rotatably installed in the storage box IK. When the cam 25 is manually rotated, the stripping salt roller 19 is connected to the separation roller 10. direction to form a gap of controlled width.

A drive motor 30 (schematically shown in FIG. 1) continuously drives the drive shaft 16 through a drive belt 31.

The connection between the drive belt 31 and the drive shaft 16 is omitted for clarity of illustration. Auxiliary drive shaft 23
is driven by a drive motor 33 via a drive belt 32 and connected to the stripping salt roller 19 by a drive belt (not shown) K.

The guide plate 34 connects the drive roll 15 and the auxiliary roll 18.
from near the gap formed between them to a conventional stacker wheel 35 rotatably mounted on the storage box 1.

The guide plate 34 and the end plate 36 constitute a take-out hopper 37.

The drive roll 15 and the auxiliary roll 18 constitute a paper sheet detection device, which simultaneously detects the passage of two or more banknotes and counts the banknotes. The driving orifice roll and the auxiliary roll are placed at a distance shorter than the width of the counted filter paper sheets.

The apparatus shown in Figure 1 is based on related Japanese Patent Application No. 59-1.
No. 52,224, which is fully described and claimed in No. 52,224.

The shaft 14 is hollow, non-rotatably supported by the storage box 1, and has two auxiliary rolls or roller assemblies 18. These structures are identical and each contacts a respective drive roll 15.

Each roller assembly 18 consists of a roller bearing.

The roller bearing has an annular outer race 38, an annular inner race 39, and a bearing section 40 between the outer race and the inner race. The bearing is mounted coaxially around the shaft 14 and on the annular rubber section 41 . The metal pin 42 contacts the radially inner surface of the inner race 390 and extends through the rubber portion 41 and the opening 43 in the shaft 14 into the shaft.

A molded plastic storage box 44 is installed within the shaft 14 and consists of a central tubular section 45 integral with the end section 4G. Each end 46 has a bore 47 that communicates with tubular section 45 .

A set of light emitting diodes 48 is provided at the inner end of the bore 47, and a 1ffi phototransistor 49 is provided at the outer end of the bore 47. In order to make the diagram easier to separate, a portion of the connecting wire from the light emitting diode 48 and the phototransistor 49 is shown. In fact, these wires
Extending along the shaft 14 to its exterior is the monitor circuitry described below. The monitor circuitry is ready for assembly. All wires extend from the same end of the shaft.

Each of the sections 46 of the storage box 44 also has an opening 50. The opening 50 communicates with the bore 47 and is aligned with the opening 32. Pin 42 extends through opening 50 and into bore 47 .

Details of the circuit elements are shown in FIG. FIG. 4 shows two light emitting diodes 48 and two phototransistors 4.
9, each of which is connected to a power source 51. The part surrounded by the dotted line in the illustrated circuit is the part installed in the plastic storage box 44. The output from each phototransistor 49 is returned to the power supply 51 via a respective voltage comparator 52. The output from comparator 52 is
Microcombiner 531C is sent. Microcomputer 53 is connected to a conventional counter and error indicator 56.

First, the drive roll 15 is rotated, and with no paper between the drive roll 15 and the roller assembly 18, all the deviations of each roller assembly 18 due to the compression of each elastic part 41 adjacent to the drive roll 15 are Detection is performed at 40 equal intervals throughout one revolution of the roller assembly 18 in a manner described below. Each rubber part 4 in the radial inward direction
1 compression involves each bin 420 moving radially inward. Each light emitting diode 48 continuously emits light, which in turn causes each phototransistor 49 to turn on, typically partially. As the pins 42 move radially inward, they gradually cover the optical path from the light emitting diode to the phototransistor 49, increasing the amount by which the phototransistor 49 is turned off. The output from phototransistor 49 (shown in FIG. 5) is sent to voltage comparator 5.
Sent to 2. Using successive approximation techniques, the microcomputer 53 instructs the comparator 52 at 40 sampling positions equidistantly spaced around the drive roll 15 (these are non-rotationally mounted on the shaft 16, not shown). (determined by monitoring the timing disk), the output is compared with the voltage value supplied to comparator 521C via D/A converter 55. This generates 40 sample voltage values which are stored in respective memories 54 as guide surface shapes or data levels. A typical shape is shown by line 57 in FIG. The 40 sampling positions occur between the origin of the graph in FIG. 57' included. FIG. 5 shows the voltage input to the comparator 52 over a number of rotations of the roller assembly 18, and the guiding shape consisting of line 57 and dotted line section 57' is generally the same at each section OA, AB, BC, and CD. It turns out that.

A first voltage threshold is configured and set by a constant difference on line 570. This difference is slightly larger than the expected change in phototransistor output voltage due to electrical noise, but also smaller than the expected change in output voltage due to the passage of what is expected to be the thinnest bill. The first threshold in the shape of the difference on the data level 57 can be set during the manufacturing process of the device or later by the user.

In practice, bundles of banknotes of the same size (same thickness and length) are placed in the input hopper 4. Drive motors 30 and 33 are activated, causing drive shaft 16 and auxiliary drive shaft 23 to rotate. picker wheel 5
The rotation pushes the banknotes out from under the bundle of banknotes towards the gap 38 between the cross-cutting roller 19 and the minute roller 10. As the stripper roller 19 rotates in response to the rotation of the auxiliary drive shaft 230, the stripper roller 19 engages the adjacent banknote and carries it through the guiding surface 8 between the auxiliary roller 18 and the drive roller 15. into the gap 58 formed between the two. Stripping port-219 and separation o-? The width of the gap between the banknotes 10 and 10 prevents one or more banknotes from being fed past the stripping roller 19.

Due to the continuous rotation of the shaft 16, the banknotes are fed between the drive roller 15 and the auxiliary roller 18, and then passed through the guide plate 3.
4 to a stacker wheel 35. The stacker wheel 35 is rotated by the drive motor 30,
The banknotes sent to the take-out hopper 37 are stacked.

Each light emitting diode 48 continuously emits light, and the light waves impinge on a respective phototransistor 49, which conducts collector current at an initial level. Each pin 42 typically partially covers the optical path. banknote 59
is the drive roll 15 and each roller assembly IJ1
8, the banknote is picked up and transported through said gap, and each rubber part 41 receives pressure applied from the outer race 38 through the bearing part 40 and from the inner race 39. compressed radially inward by the pressure. This movement is accompanied by a radially inward movement of each bin 42, which covers the light path from light emitting diode 48 to phototransistor 49, so that the light sent to phototransistor 49 is further attenuated.

At each of the 40 sampling positions, the micro combinator 53 adds a preset difference to the respective voltages stored in the memory 54 and calculates the first
62 and send these to the comparator 52.

An example of a group of output signals generated by the presence of a single bill in gap 58 is shown at line 60 in FIG. It can be seen that a portion of line 60 is the same as line 57, but is substantially different over the sampling area OA. The comparator 52 has a value of 40 and a micro combination.
40 from 53 are sequentially compared, and an output is generated on line 61 (FIG. 4) K as to whether the threshold value 62 has been exceeded. The difference between the signals represented by the two-in 60 and the corresponding portion 57' of the memorized shape is t'ttx uniform, as would be expected from a banknote having a more or less constant thickness. If the threshold 62 is exceeded at a large number (usually less than 40, since the length of the bill is generally less than the circumference of the drive wheel) at a large number of sampling locations, it is assumed that the bill has passed through the gap. When the presence of a banknote is detected by both phototransistors 49, the micro combinator 53
causes device 56 to increment the count by one. Furthermore, in response to the supply of the first banknote, a single leaf sledge drawer 3 is calculated by the microcombinator 53. The single-sheet sledge difference represents the difference between the comparator input and the stored data shape corresponding to a banknote that has a margin of one-half the thickness of the detected banknote. For example, it is 0.625 times the thickness of the detected banknote. You can also use other fractions.

The micro combinator 53 also calculates a double sheet threshold 64 corresponding to a sheet thickness of 1.A and a triple sheet threshold 67 corresponding to a sheet thickness of 2.A, but for other Multiples can also be used.

For the remaining bills in hopper 4, the voltage signal input to comparator 52 is compared to each of the new thresholds at each of the 40 sampling locations to determine which threshold has been exceeded. Ru. The details will be described later.

For banknotes made of typical materials, the phototransistor 49 rarely provides exactly the same output during two consecutive complete rotations of the drive roll 15 and the auxiliary roll 18. This is caused by dust falling from banknotes. Thus, for example, even if no bill is present in gap 58, the subsequent voltage input to comparator 52 will be at line 66 in FIG.
It may have the shape shown below. However, since this change is also smaller than the difference constituted by the difference between the first threshold 62 and the data 57, the micro combinator 53 detects that the threshold 62 is not exceeded and therefore the banknote It is determined that there was no passage.

Furthermore, over a period of time, the output from phototransistor 49 can vary significantly. This occurs by an amount similar to that expected from the passage of banknotes. In order for the device to still function, the micro combinator 53
stores a new shape in the memo 1754K in place of the previously stored shapes 57 and 57' just before a new bundle of banknotes is counted. Since the first threshold 62 is configured by a difference, it is automatically adjusted to KIIMI.

In some cases, a weighed bill is passed through the gap, in which case one comparator 52 will indicate the presence of a bill and the signal sent to the other comparator 52 will indicate that no bill is present. suggest. Microcombinator 53 detects from the signals sent along line 61 that these signals represent different differences and causes device 56 to display an appropriate error message.

The microcomputer 53 can be programmed to detect folded banknotes, as well as banknotes fed diagonally, and even half banknotes@One more important feature determines the length of the banknote fed It is possible.

- Output t from the phototransistor 49 is monitored at 8 or more points, and as the number of points increases, a more accurate determination of the length of the bill to be fed can be carried out. This is particularly important as it yields a time-independent measurement of banknote length.

After supplying the bundle of banknotes, the micro combinator 53
erases the stored differences representing thresholds 63, 64, and 65, but the difference representing threshold 62 remains permanently stored. The device is then ready to process a new bundle of banknotes.

As explained above, when determining the thickness at a number of locations on the first reference banknote being fed, the "length" in the direction of movement can also be determined.

This information is then used in conjunction with the thickness data to aid in later banknote counting and to determine whether overlapping, short or long banknotes have been dispensed.

In particular, the following information is derived by the microcomputer 53:

a) Two banknotes are counted if the measured length of the double-thickness banknote in combination with the length of the single-thickness banknote is equal to two partially overlapping banknotes. Otherwise, an error condition is introduced.

b) If one detector detects double thickness and the other detects single thickness, and the length is correct, it represents a banknote with tape on one side. The effect of the tape can be ignored. Similarly, if a portion of the correct length bill is detected as double thickness, the double thickness output signal may be ignored.

C) When a thickness equal to or more than 2 times the banknote thickness is detected, and the pick output signal exceeds the triple paper leaf threshold 67 over a part of the detection area, the triple paper banknote thickness is detected. An error condition will be displayed as if the

For example, one bill folded in half may be fed sandwiched with another bill.

In some cases, the original banknote may not be the single "correct" banknote, and therefore the length of the fake banknote, the thickness of the banknote, the fake banknote, etc.
and an associated false calculation threshold may be determined. Subsequent processing of the banknote indicates whether the banknote is problematic.

The following is a simplified example; the thickness of a single banknote is rTJ.
The length of a single banknote in the feeding direction is denoted by "L".

[First Example] It is assumed that the banknotes fed first are double-thickness banknotes, for example, two overlapping banknotes, and the thickness is 2T. In this case, the single sheet threshold is set to a value slightly larger than T, and the length is set to LK since the bills are completely overlapped. When the next bill is detected, the single paper threshold 63 is not executed, but
Since the first threshold 62 is exceeded, the presence of paper is detected.

The micro combinator 53 infers from this that it has detected a small banknote (by the single paper threshold) and generates an error. In this state, the microcombiator 53 generates an error signal, causes the device 56 to display an appropriate message, and also stops the drive motors 30 and 33.

Margins Below (Second Example) In this example, the first banknotes to be fed consist of two partially overlapping nine banknotes. Due to thickness averaging, the single sheet threshold will not be greater than the thickness T of the next delivered bill, so the first example situation does not cause an error condition. But in this case, the length of the next banknote is decreasing, so the length of the next banknote is less than the length determined from the length of the first overlapping banknote, and this again causes the error condition to appear. be done.

[Third Example] This example also assumes that the first banknote consists of two partially overlapping banknotes. In the second example, it was assumed that the lengths measured by both detectors were approximately the same. However, due to the nature of banknotes, one or both banknotes may be tilted, and therefore the measured length may be different for each detector. Therefore, the micro combinator 53 compares all the differences in the measured lengths with the threshold value, and if this difference is too large, an error signal can be generated. [Fourth example] , preset the maximum length threshold,
If both detectors detect a length that exceeds this threshold, they generate an error signal.

[Fifth example] If a banknote is detected by only one detector, an error state indicating that the supplied banknote is a half banknote is displayed, for example.

Considering the above example, it can be seen that the threshold set based on the results of the first banknote supplied is reliably representative of subsequent banknotes. If the banknotes following the first banknote are also duplicated or overlapping, a check may also be carried out for at least some of the banknotes following the first banknote.

[Brief explanation of drawings]

Fig. 1 is a schematic side view of the device, Fig. 2 is a partial cross-sectional view of a part of the nine paper leaf detection device with parts omitted for clarity, and Fig. 3 is the same as shown in Fig. 2. 4 is a circuit diagram illustrating a circuit for connecting to the sheet detection device of FIG. 2, and FIG. 5 is a diagram illustrating a representative output signal from the detection assembly. FIG.

Claims (12)

[Claims] (1) A method for monitoring the passage of a sheet through at least one sheet detection assembly of a sheet feeding device, each sensing assembly generating an output signal that varies in level depending on characteristics of the sheet; The method includes setting a single sheet output signal threshold for each of the sensing assemblies at a level that is exceeded by an output signal generated by the sensing assembly as a sheet passes through the sensing assembly; monitoring the output signal when it exceeds a threshold, and presetting a first threshold at a predetermined distance from the data output signal level that is activated when no paper is detected. and the preset amount is set such that the first threshold is not exceeded as a result of random noise variations in the output signal, but when all paper sheets to be monitored pass through the detection assembly. monitoring the size of the output signal relative to the data level when the output signal first crosses a first threshold corresponding to the passage of a first sheet; A method for monitoring the passage of a sheet, characterized in that it generates a single sheet threshold from the monitored size and then monitors when said output signal exceeds said threshold. (2) The method according to claim (1), further comprising: an error when the output signal exceeds the first threshold but does not exceed the single sheet threshold; A method consisting of generating a signal. (3) A method according to claim 1 or 2, further comprising generating a double sheet threshold from the monitored size, wherein two or more sheets A method comprising: when an overlapped sheet passes, the level of an output signal from said detection assembly exceeds said double sheet threshold. (4) The method according to any one of claims (1) to (3), further comprising generating a triple sheet threshold from the monitored size, A method in which the output signal level from the detection assembly exceeds the triple sheet threshold upon the passage of more overlapping sheets. 5. The method of claim 4, further comprising generating an error signal when the output signal level exceeds the triple sheet threshold. (6) In the method of claim (4), when based on claim (3), the output signal level from the detection assembly is such that the double sheet threshold is 2 when exceeding but not exceeding the triple paper leaf threshold.
A method consisting of detecting the passage of overlapping sheets of paper. 7. A method according to any one of claims 1 to 6, wherein the output signal from the detection assembly varies depending on the thickness of the sheet. (8) A method according to any one of claims (1) to (7), further comprising monitoring the length of the sheet passing through each detection assembly. (9) The method of claim (8), wherein a sheet of paper is moved past each of said detection assemblies at a substantially constant speed, and said length monitoring step comprises: A method consisting of monitoring the time during which a leaf threshold is exceeded. (10) In the method according to either claim (8) or (9), further, the monitored sheet length is determined by the length of the first sheet fed through the detector. A method consisting in generating an error signal if the length of the sheet differs significantly from the monitored length. (11) The method according to any one of claims (1) to (10), wherein two detection assemblies are provided laterally at a distance from each other across the sheet supply path. , the method comprising monitoring the output signal from each detection assembly and detecting the passage of an incorrectly fed sheet. (12) An apparatus for monitoring the passage of a sheet through at least one sheet detection assembly, wherein the detection assembly is used to generate an output signal whose level varies depending on characteristics of the sheet; The apparatus stores, for each said detection assembly, a single paper output signal threshold corresponding to a signal level that is exceeded by an output signal generated by said detection assembly as a sheet passes through said detection assembly. a first preset threshold at a predetermined distance from the data output signal level which operates when no sheets are detected; In the means for storing, the preset amount is such that the first threshold is not exceeded as a result of random noise variations in the output signal, but when all sheets to be monitored pass through the detection assembly. It is an amount that is exceeded by
The monitoring means is configured to set the first threshold such that the monitoring means is used to monitor the size of the output signal relative to the data level when the output signal first exceeds the first threshold. Apparatus comprising means for storing and calculating means for calculating a single sheet threshold from the monitored size and storing the single sheet threshold in said storage means.