GB2298504A - Sheet counter - Google Patents

Abstract

A sheet counter has an elongate element 18 in which is formed a suction port 19. A pin 24 is arranged to orbit around the element 18, and to transfer sheets of paper, one at a time, from the ported side of the element 18 to the other side thereof. A vacuum pump 30 is connected by duct 26 to the port 19, and a differential pressure transducer 35 has its two ports connected to the duct 26, respectively adjacent the pump 30 and the element 18. The output of the differential pressure sensor 35 is used to generate a count signal 38, by detecting when a sheet closes the port 19. To avoid erroneous counts, the sensor output 35 may be combined with a further signal 29, generated only when a sheet may be expected to close the port 19.

Description

SHEET COUNTER This invention relates to a sheet counter, and in particular - but not exclusively - to a counter for sheets of paper.

A known form of sheet counter, primarily intended for counting sheets of paper, has an elongate element which is inserted into the corner region of a stack of paper, the element having on one side a port which is connected back to a low pressure source. An elongate member having its axis substantially parallel to that of the element orbits around the latter and serves to transfer the corner regions of sheets, one at a time, from one side of the element to the other. The corner region of the next-to-be-counted sheet of paper in the stack is lifted from the stack by air drawn through the port until that sheet rests on that element and closes off the port. The element is moved through an acute angle to open a gap for the elongate member, on orbiting round the element, to pass between that sheet and the remainder of the stack and transfer that sheet to the other side of the element.

A pressure sensor is disposed to sense the pressure in the duct leading to the port, as close as possible to that port in order to allow the generation of a count signal. Each time the port is closed off, the pressure in the duct falls significantly below atmospheric pressure, and that pressure fall is detected and used to produce a count signal. In order to reduce the likelihood of an erroneous count, often the count signal resulting from the sensing of the pressure is combined with a position signal, so that a valid count will be generated only if a pressure change is detected at the time a sheet should close the suction port.

Unfortunately, counting errors sometimes occur in sheet counters as described above, on account of significant pressure fluctuations which may arise in the low pressure source. Also, a significant change in atmospheric pressure can affect count reliability.

This leads to a requirement to calibrate the equipment from time to time, and also when it is first installed, especially if the equipment is installed at some geographically elevated site.

It is an aim of the present invention to provide a sheet counter which is able reliably to count sheets which, one by one, close off a port through which air is drawn during operation of the counter.

According to the present invention, there is provided a sheet counter including an element having a suction port over which the sheets to be counted are caused to lie in sequence one after another, a source of reduced pressure, and duct means connecting the suction port to the source of reduced pressure, the sheet counter further comprising a differential pressure sensor having two sensing inputs, one of which is connected to sense pressure within the duct in the vicinity of the suction port and the other of which is connected to sense the pressure at or adjacent the low pressure source, the output of the differential pressure sensor being used to generate a count signal when a sheet closes off the suction port.

In the sheet counter of this invention, a differential pressure sensor is used to sense the pressure drop through the duct arrangement which connects the low pressure source (which usually will be a vacuum pump) to the suction port in the elongate element of the sheet counter. A count threshold may be established, so that a count signal may reliably be generated whenever the suction port is closed off, and no count signal will be generated whenever the suction port is open. This arrangement isolates the counting of the sheets from variations in the pressure of the low pressure source, such as may be caused by the performance of the vacuum pump used to create that source, and also from variations in atmospheric pressure.

In a case where the duct means inter-connecting the low pressure source to the suction port includes a filter, it is preferred for the pressure drop across that filter to be included in the sensing by the differential pressure sensor.

Though one input of the differential pressure sensor is connected to sense the pressure adjacent the suction port, in fact trials have shown that it is possible for the pressure to be sensed at some point distant from the suction port itself, so long as there is still a sufficient length of duct means between the point at which the pressure is sensed and the low pressure source to generate a pressure drop when air flows along the duct means. The greatest pressure differential will be sensed the closer the sensing point to the suction port, but adequate and reliable operation may still be achieved when the differential pressure sensor is arranged to sense a shorter length of the duct means.

The differential pressure sensor may take a variety of different known forms for such a device.

Preferably however, the sensor is a Piezo-resistive device which has an electrically adjustable off-set, to allow the generation of an electrical output when the sensed pressure difference exceeds or is less than a threshold value set by the off-set. The electrical output may then be amplified and processed as required, in order to give a count signal appropriate for the particular equipment within which the sensor is incorporated.

Preferably, the sheet counter is of the design described above, and so has an elongate element for insertion in the corner region of a stack of sheets to be counted, and an elongate member arranged to lie substantially parallel to said element and which member is arranged to orbit around the element. The element has the suction port in the side thereof to which sheets are drawn, before being transferred to the other side of that element by the orbiting member. A sensor for the position of the elongate member which orbits around the element may be provided, and which gives an output at the time a count signal may be expected, which output is combined with the output from the differential pressure sensor so as further to minimise the likelihood of an erroneous count.

By way of example only, one specific embodiment of sheet counting apparatus of this invention will now be described in detail, reference being made to the accompanying drawings in which: Figure 1 is a perspective view of a known form of sheet counter, to which the invention may be applied; Figure 2 shows the known pressure sensing arrangement which conventionally is employed with the sheet counter of Figure 1; and Figure 3 shows the pressure sensing arrangement of the present invention, for incorporation in the sheet counter of Figure 1.

Figure 1 shows a known form of sheet counter comprising a frame 10 which supports an electric motor 11 drivingly connected by means of toothed belts 12 and 13 to two cranks arranged one on each side of the frame, respectively. In Figure 1 only one crank 14 can be seen; the second crank is similar and mounted on the same shaft as pulley 15 driven by belt 13. Crank 14 is connected by a complex linkage 16A, 16B, 16C to a pivoted arm 17 which supports an elongate element in the form of a blade 18, in which is provided a suction port 19. The second crank is connected by a further complex linkage 20A, 20B, 20C to another arm 21 which is itself mounted on a third crank (not shown) driven by pulley 15 through meshing gears 22 and 23. Arm 21 carries an elongate member in the form of a rotatable pin 24 the axis of which is parallel to that of the blade 18.

The arrangement described above is such that the blade 18 performs an essentially rocking movement approximately based on its leading edge 25, while the pin 24 orbits around that blade. Sheets in a stack are counted by inserting the blade 18 in the corner region of the stack and then transferring the sheets one at a time from one side of the blade to the other, by the orbiting action of pin 24. The next sheet to be counted is drawn on to the blade 18 by suction applied to port 19, through pipe 26 connected back to a low pressure source.

A pressure sensor 27 is arranged to sense the pressure in a duct (not shown) within the frame 10, which connects port 19 to pipe 26. A mechanical threshold can be set within the sensor 27, such that a switch is turned on when the detected pressure is below the pre-set threshold.

A ring 28 is attached to gear 23 and carries a magnet, and a Hall-effect switch 29 is mounted adjacent the ring 28, whereby the switch will be turned on each time the magnet passes that switch. Switch 29 is connected in series with the switch of pressure sensor 27, whereby an output signal will be generated only when both switches are turned on. The position of the magnet of ring 28 is set so that the Hall-effect switch 29 will be turned on only when it may be expected that a sheet to be counted will overlie port 19. In this way, the likelihood of erroneous counts may be reduced.

Figure 2 diagrammatically shows the pressure sensing arrangement employed in the counter of Figure 1. A vacuum pump 30 is arranged to draw air along pipe 26 from the port 19 in the suction blade 18. The pressure sensor controls switch 31 whereby that switch is operated dependent upon the sensed pressure relative to atmospheric pressure. The activation of switch 31 depends upon the pre-set threshold of the sensor 27, which threshold lies somewhere between atmospheric pressure and true vacuum. If the atmospheric pressure changes, it follows that the activation point of switch 31 has to change in order to maintain the same differential to atmospheric pressure. In practice, this involves adjustment of sensor 27.

In Figure 3, there is illustrated the embodiment of pressure sensing arrangement of this invention, for use with the counter of Figure 1. Here, a differential pressure sensor 35 is arranged to sense the pressure both at the vacuum pump 30, and also at a position adjacent the suction blade 18. If the vacuum pump 30 includes a filter (as is usually the case), then it is preferred for the pressure sensing at the pump to be on the upstream side of that filter 36.

The output from the pressure sensor 35 is combined in an AND-gate 37 with the signal from a position sensor, which may again be the Hall-effect switch 29.

The output from the AND-gate 37 is the count signal 38, which will be produced only if the port 19 is covered at the time it is expected to be covered, by a sheet to be counted.

When the counter is initially energised, a first reading is taken before the vacuum pump is operated.

This reading represents the condition when the suction port 19 is covered by a sheet and hence near vacuum is achieved. As there is no flow through the pipe 26, there is no pressure drop across the sensor 35.

A second reading is taken when the vacuum pump is operated, but still with the port 19 open. In this case, there is maximum airflow through the pipe 26 resulting in the maximum pressure drop along that pipe and so the maximum pressure differential across the sensor 35. This is therefore representative of the condition where a sheet not corner has been separated by the counting mechanism.

A control arrangement may be arranged to permit setting of a threshold at a some value between the first and second readings. The set value should be such as to ensure reliable counting, having regard to the particular installation.

Claims (8)

1. A sheet counter including an element having a suction port over which the sheets to be counted are caused to lie in sequence one after another, a source of reduced pressure, and duct means connecting the suction port to the source of reduced pressure, the sheet counter further comprising a differential pressure sensor having two sensing inputs, one of which is connected to sense pressure within the duct in the vicinity of the suction port and the other of which is connected to sense the pressure at or adjacent the low pressure source, the output of the differential pressure sensor being used to generate a count signal when a sheet closes off the suction port.

2. A sheet counter as claimed in Claim 1, wherein a filter is provided in the duct means connecting the low pressure source to the suction port, the pressure drop across that filter being included in the sensing by the differential pressure sensor.

3. A sheet counter as claimed in Claim 1 or Claim 2, wherein the differential pressure sensor comprises a Piezo-resistive device.

4. A sheet counter as claimed in any of the preceding Claims, wherein the switching point of the differential pressure sensor is adjustable.

5. A sheet counter as claimed in any of the preceding Claims, wherein the counter includes an elongate element for insertion in the corner region of a stack of sheets to be counted, the element having said suction port formed thereon, and an elongate member arranged to lie substantially parallel to said element and which member is arranged to orbit around the element.

6. A sheet counter as claimed in Claim 5, wherein there is a sensor for the position of the elongate member which orbits around the elongate element, which sensor gives an output at the time a count signal may be expected.

7. A method of setting-up a sheet counter according to any of Claims 1 to 6, wherein a first reading of the differential pressure sensor is taken before the low pressure source is operated, a second reading of the differential pressure sensor is taken with the low pressure source operated but with the suction port open, and then the operating threshold for the differential pressure sensor is set at a predetermined value lying between said first and second readings.

8. An operating method for a sheet counter substantially as hereinbefore described, with reference to the accompanying drawings.