It is already known to provide apparatus for counting sheets held in a stack, the apparatus comprising a set of rotatably mounted suction spindles mounted for movement past a stack of sheets to be counted, vacuum supply means connected to the spindles, whereby as a suction spindle passes the stack, a vacuum is supplied to the spindle so that the topmost sheet is deflected from its initial position; and monitoring means for monitoring the number of deflected sheets. Such apparatus is hereinafter referred to as of the kind described and is commonly referred to as a "spindle counter".

Most spindle counters require a minimum pressure (vacuum) to be maintained within the system with the counting being achieved by means of external electromagnetic/photoelectric sensors which operate independently of the vacuum system provided the minimum pressure is maintained. An example is described in GB-A-2041888.

Another approach is to detect changes in the pressure or vacuum supplied to the spindles. An increase in vacuum (decrease in pressure) corresponds to a sheet being deflected and this change can be used to implement a count. Examples of such spindle counters are described in GB-A-2238411, GB-A-2238895, and GB-A-1530652.

In some of these known spindle counters, for example those described in GB-A-2238411 and GB-A-2238895, it is necessary to index the spindles to a known position prior to the start of the count process. This is undesirable.

A further problem with systems such as that described in GB-A-2238895 is that if a spindle fails to deflect a note during a count process, the system will stop. This leads to problems in that the whole process has to be restarted.

A problem which is encountered in various sheet feeding systems in which sheets are taken from a stack, but which is particularly significant in the case of apparatus of the kind described, is in controlling the force by which the stack of sheets is urged towards the sheet processing position. Conventionally, this has been under the control of a tension spring as described for example in GB-A-2028282 and US-A-4272067 or a bellows as described in GB-A-2039112. However, in neither case does the force remain constant throughout the feed operation which is undesirable for reasons in connection with monitoring pressure levels.

In accordance with one aspect of the present invention, we provide a method of feeding a stack of sheets to a sheet processing position, the method comprising mounting the stack against a pivoted support plate; and causing a drive motor to pivot the support plate towards the sheet processing position while sheets from the stack are being processed.

In accordance with a second aspect of the present invention we provide apparatus for feeding a stack of sheets to a sheet processing position, the apparatus comprising a pivoted sheet stack support plate against which a stack of sheets is provided in use; and a motor coupled to the support plate to move the support plate towards the sheet processing position while sheets from the stack are being processed.

In the past, a motor has been used to move the support plate from a retracted position in which a stack of sheets can be loaded onto the plate and the processing position where the stack of sheets is ready to be processed. Thereafter, the support, plate has been urged towards the sheet processing position during processing under the control of a spring or bellows. We provide instead a controlled movement of the support plate towards the sheet processing position under the influence of the motor which enables the force with which the stack is urged towards the sheet processing position to be closely controlled and preferably kept substantially constant. By using the same motor which is used conventionally to move the plate between the retracted and processing positions, no additional drive means is required.

Typically, the drive motor is coupled to the support plate via a spring, such as a tension spring. In this case, the end of the tension spring coupled to the drive motor is moved against its tensioning direction to cause the plate to pivot towards the sheet processing position, the spring accommodating small vibrations of the plate.

Preferably, the drive motor is coupled to a rack to which one end of the spring is connected, the other end of the spring being attached to an arm connected to the support plate and pivoted about the same axis as the support plate whereby rotation of the arm causes rotation of the plate. In this case, the arm and plate are conveniently mounted to the same shaft.

The rack may also be rotatably mounted about the same nivot axis as the arm and the plate.

Preferably, the rack includes a laterally extending pin which is received in a slot in the arm whereby the plate is moved to its retracted position by moving the rack so that the pin contacts an end of the slot and thereafter pivots the arm.

Typically, the apparatus further includes a clamp arm which is urged into contact with the stack of sheets on the plate. This is particularly useful where the apparatus is used in connection with a spindle counter of conventional form or in accordance with apparatus described in EP-A-0616300.

It will be understood that all aspects of the invention are suitable for handling and counting sheets of various types but they are particularly suitable for use with banknotes.

An example of a spindle counter according to the present invention will now be described with reference to the accompanying drawings, in which:-

• Figure 1 is a schematic diagram of the apparatus with the head in a first position;
• Figure 2 is a view similar to Figure 1 (with parts omitted) with the head in a second position;
• Figure 3 is a view similar to Figure 2 with the head in a third position;
• Figure 4 illustrates the centre spindle in more detail;
• Figure 5 illustrates a typical count sequence;
• Figure 6 illustrates the variation of sensed pressure against a constant threshold;
• Figure 7 illustrates the variation of sensed pressure against an adaptive threshold; and,
• Figure 8 is a schematic, perspective view of part of the sheet stack control system.

The apparatus shown in Figures 1 to 3 is of substantially conventional form, particularly the construction of the head 1. The head 1 comprises five substantially equally angularly spaced suction spindles 2-6 rotatably mounted to a main support 7 which itself is rotatable under the control of a head motor 8. The support 7 is rotated in use in an anti-clockwise direction (as seen in Figure 1) while the suction spindles 2-6 are rotated in a clockwise direction. The gear assemblies for achieving these rotations are well known and will not be described further.

The support 7 has a central bore 9 extending along its axis and communicating with a set of five ports 10 which communicate with respective suction spindles 2-6. The support 7 rotates about a central spindle 11 mounted within the bore 9 and shown in more detail in Figure 4. The central spindle 11 has a central bore 12 which is connected to an exhaust port 13 at one end which in turn is connected to a head valve 17, filter 18 and a vacuum pump 19. At its end level with the ports 10, the bore 12 terminates in port 16. Circumferentially spaced exhaust ports 14,15 are provided for communication with the ports 10. Between the ports 14,16 is a counting port 20 which communicates through a bore 21 in the central spindle 11 with a pressure transducer 22.

The pressure transducer 22 is of conventional form and generates an electronic signal related to the sensed pressure. This signal is fed to a microprocessor 23 connected to control the head motor 8, a stack motor 24, and a display 25. The operation of the processor 23 will be described in more detail below.

A stack of sheets 26 to be counted are loaded onto a support plate 27 pivoted to a shaft 28 (Figure 2) the end of the stack nearest the shaft 28 being clamped in position by a clamp pin 29 mounted on an arm 30.

In operation, the support plate 27 carrying a stack of sheets such as banknotes is brought to the position shown in Figures 1-3 and the processor 23 is then instructed to control the head motor 8 to start operation. The head motor 8 rotates the support 7 in an anti-clockwise direction thereby causing the spindles 2-6 to rotate in a clockwise direction and the first spindle 2 will arrive at the stack 26 (Figure 1). A vacuum is supplied from the vacuum pump 19 to the port 16 so that as the port 10 associated with the spindle 2 approaches the position shown in Figure 1, the vacuum will be communicated through the port 16 and port 10 to the suction spindle 2. The suction spindle 2 will thus suck the topmost banknote against its outer periphery. Further rotation of the support 7 and spindle 2 draws the topmost banknote (shown at 31 in Figure 2) away from the stack. As the spindle 2 continues to rotate, the port 10 associated with the spindle 2 will move round to overlap the vacuum and counting ports 16,20. This has the effect of connecting the vacuum to the transducer 22 via the bore 21 so that the transducer sees the high level of vacuum. As the head 1 continues to rotate, the port 10 becomes disconnected from the vacuum port 16 remaining connected only to the counting port 20 (Figure 2). Shortly after this, as the head continues to rotate, the port 10 associated with spindle 2 will overlap both the counting port 20 and exhaust port 14. This allows the vacuum present in the sealed spindle to be opened to the atmosphere via ports 14 and 15, cancelling the stored vacuum. This also opens the counting port 20 to the atmosphere. At this time the sheet held by the spindle 2 is released due to the loss of vacuum and further rotation brings the port 10 solely into line with port 14 (Figure 3). As the head 1 rotates further, the sequence repeats for the next spindle 6 and so on.

Due to the overlapping action of the counting port 20 with the vacuum and exhaust ports 16,14, the transducer 22 will see first a rise in vacuum, followed by a drop as the port 20 is connected to the exhaust port 14. This means that for each sheet the transducer will see a pulse, allowing the processor 23 to count these pulses and thereby count the number of sheets in the stack. This number is then displayed on the display 25 which is in the form of a LCD or the like.

Figure 5 illustrates a typical count sequence. Initially, the processor 23 activates the head motor 8 (step 41). The head 1 then begins to rotate and in this case, the first head 2 fails to pick the topmost sheet from the stack. Consequently, as shown in 42, only a small rise in vacuum level is measured. This rise does not exceed a predetermined threshold 43A and consequently no count pulse is generated within the processor 23. The next spindle successfully picks the topmost sheet thus causing a significant vacuum to be communicated into the counting port 20 so that the transducer 22 senses a drop in pressure which exceeds the predetermined threshold 43A. This is indicated at 43 in Figure 5. As soon as the sensed vacuum exceeds the threshold, the processor 23 will generate a count pulse 44 which increments an internal count while the count to date is displayed on the display 25.

This process continues as shown in Figure 5 but where a spindle fails to pick a sheet, as at 45, no count pulse is generated. After the failure 45, the next spindle successfully picks the note so that counting continues until the last sheet is picked as shown at 46. After this, two further spindles will attempt to pick sheets from the stack but since no sheets will be picked, only small changes in vacuum level will be sensed as shown at 47 and 48.

The processor 23 is programmed to expect a count pulse within a certain time period and consequently if the time period passes without a count pulse being generated then the processor decides that the counting process should terminate and switches off the head motor at step 49. The time period will usually be long enough to permit two or three spindles to attempt to pick a note.

It will be seen from this description that there is no need to position the head 1 at a particular index position prior to commencing the count process. Counting is automatically carried out and although it is likely that for an initial period no sheets will be picked as the sheets are being fed towards the spindles on the support plate 27, the processor 22 can accommodate this by not incrementing the count. Providing a note is counted before an initial, predetermined period expires then the process will continue. If for some reason no sheet is detected within that predetermined period then the head motor 8 will be stopped.

The system determines that the end of a count cycle has taken place in a similar way although the predetermined period could be different, usually shorter, than the predetermined period at start-up. For example, the predetermined period at start-up could correspond to the passage of three or four spindles past the stack while the predetermined period at the end of a count cycle could correspond to the passage of two or three spindles.

In the example just described it has been assumed that the vacuum level threshold is constant throughout the counting process. Figure 6 illustrates such an example in which the threshold level is indicated at 50. As can be seen, the vacuum signal drops with time due to the decrease in the pressure with which the stack is urged towards the spindles. This could result in a vacuum level due to a sheet not exceeding the threshold with the result that the sheet is not counted.

To overcome this problem, the processor 23 can monitor and store in a store 100 the last N vacuum threshold levels which exceeded a threshold (N is typically eight) and were used to increment the count and can compute an average of those N levels from which a new threshold is calculated. For example, the processor could compute the average of the last three vacuum levels which exceeded a threshold and define the new threshold as being a proportion, for example 25-50%, of the new average. Figure 7 illustrates a threshold level 51 which is varied using this technique and it can be seen that later pulses although having a smaller absolute vacuum level magnitude, exceed the current threshold by similar proportions to the initial levels.

The sheet stack is, as previously described, mounted on a support plate 27 which in turn is mounted on a feed shaft 28 for rotation therewith. The system for controlling the orientation of the shaft 28 is shown in more detail in Figure 8. The shaft 28 is rotatably mounted in bearings supported in housings 55 which are in turn mounted on a bracket 56. A shaft drive arm 57 non-rotatably mounted to the shaft 28 extends laterally away from the shaft 28 and is positioned adjacent a rack 58 rotatably mounted about the shaft 28. The teeth 59 of the rack 58 engage a drive pinion 60 which is connected to the stack motor 24 (not shown in Figure 8). The arm 57 is connected to the rack 58 via a tension spring 61.

A stop pin 62 extends laterally from the rack 58 into an aperture 63 in the arm 57. The arm 57 also carries an adjustable screw 64.

The shaft 28 also rotatably carries the clamp arm 30 which is connected in use to a torsion spring 65 to urge the clamp pin 29 against a stack held on the support plate.

The operation of the system shown in Figure 8 will now be described. Consider the position in which the plate 27 is in its forward position as shown generally in Figures 1 to 3. Following the counting of a batch of sheets, the motor 24 is activated to rotate the rack 58 in an anti-clockwise direction (as seen in Figure 8) which causes the stop pin 62 to move relative to the aperture 63 in the arm 57 and until the pin engages the lower side of the aperture whereupon the arm 57 is also rotated anti-clockwise until the adjustor screw 64 locates on the brackets 56. When this occurs, a current over limit device (not shown) stops the motor.

The stack of sheets to be counted is then loaded onto the plate 27 on which it is held by the clamp pin 29. The motor 24 is then activated to rotate the rack 58 in a clockwise direction moving the stop pin 62 away from the lower side of the aperture 63. Once the pin 63 reaches substantially the position shown in Figure 8, the tension spring 61 will start to draw the arm 57 in a clockwise direction. This movement continues not only (at a relatively fast rate) to bring the stack of sheets initially into position but also (at a relatively slow rate) during the counting operation with the tension spring exerting a reasonably uniform feed load on the sheets. The speed of the motor 24 is controlled by an over current limiter. Thus, if the note feed is too fast, then pin 62 drives up against the shaft drive arm so increasing the load on the drive motor. This increase in load is measured by a current limiting device which slows down the drive motor. In this way, a substantially constant load is imparted on the stack of sheets throughout the counting operation. The operation of this mechanism to count sheets may be improved with the addition of a damper (66) acting on the feedshaft (28).