WO1995026920A1

WO1995026920A1 - Pneumatic conveyors

Info

Publication number: WO1995026920A1
Application number: PCT/GB1995/000774
Authority: WO
Inventors: Fraser Crisfield Henderson; Derek Lum
Original assignee: Air Tube Conveyors Limited
Priority date: 1994-04-05
Filing date: 1995-04-04
Publication date: 1995-10-12
Also published as: AU2112595A; GB9406654D0

Abstract

A pneumatic conveyor of the type in which a carrier (12) is transported through tubing (10) by an air flow in the tubing (10) and a carrier detector (20) comprising means (36) for sensing a differential in the air pressure at a pair of locations (30, 34) within the tubing (10) spaced apart lengthwise of the tubing (10). There is also disclosed a detector (20) for use in such a conveyor.

Description

PNEUMATIC CONVEYORS

Background of the Invention

This invention relates to pneumatic conveyors of the type in which a carrier is transported from one station to another through tubing, the carrier being carried by means of air flow through the tubing.

Carrier detectors are used in pneumatic conveyors of the type described above in order to provide a signal indicating the position of carriers within the conveyor. Such detectors are commonly provided close to receiving stations in order to provide an indication that a carrier is about to arrive at the station.

One known type of carrier detector comprises a mechanically operable switch provided outside of the tubing and arranged to be operated by actuator means which extends into the tubing. The actuator means is arranged such that when a carrier passes the detector, the actuator means is deflected by the passing carrier, the deflection of the actuator means operating the switch to provide a signal indicative of the passing of the carrier. It has been found that the actuator means tends to wear or be broken off due to the passing carriers. The detectors are often provided in relatively inaccessible parts of the conveyor and so regular maintenance or repair of the actuator means is difficult or impossible.

An alternative type of detector comprises a light source, for example an LED, provided in the wall of the tubing and a suitable optical sensor provided in the opposite wall of the tubing and arranged to detect the breaking of the light beam emitted by the light source by the passing of a carrier through the tubing. This type of carrier detector has the disadvantage that dust within the conveyor tends to collect in recesses provided in the tubing including on the light source and optical sensor, reducing the effectiveness of the carrier detector. Such detectors are often provided in relatively inaccessible parts of the conveyor, and so regular cleaning of the light source and the optical sensor is not practical.

It is an object of the invention to provide a conveyor in which the above described disadvantages are reduced.

Summary of the Invention

According to the present invention there is provided a pneumatic conveyor of the type described above, the conveyor having a carrier detector comprising means for sensing a differential in the air pressure at a pair of locations within the tubing spaced apart lengthwise of the tubing.

The carriers used in pneumatic conveyors of the type described above include at least one seal element arranged to effect a sliding seal between the carrier and the internal wall of the tubing, in use. In order for the carrier to move along the tubing, the pressure behind the carrier must be greater than the pressure in front of the carrier. It will be recognised that in the absence of a carrier, the air pressure at said locations will be equal but when the seal element of a carrier is between the pair of locations, one of the locations will be subject to the higher pressure behind the carrier whilst the other location will be subject to the lower pressure in front of the carrier. In these circumstances, the pressure differential across the seal element will be sensed providing an indication as to the location of the carrier. Preferably, the means for sensing a differential in the pressure comprises an electrical switch and a housing divided internally by a diaphragm, the chamber defined on one side of the diaphragm communicating with the tubing at one of said pair of locations, the chamber defined on the other side of the diaphragm communicating with the tubing on at the other of said pair of locations, the switch being arranged to be actuated by movement of the diaphragm.

Movement of the diaphragm may be detected mechanically. An alternative is to attach a magnet to the diaphragm and monitor movement of the diaphragm by monitoring changes in the magnetic field, for example using the Hall effect.

The pair of locations may be spaced apart by an amount greater than the axial dimension of the seal element of a carrier to be used in the pneumatic conveyor. Where the carrier includes a plurality of seals, the locations are preferably spaced apart by an amount greater than the axial spacing of the seals.

According to a second aspect of the invention, there is provided a carrier detector for use in a pneumatic conveyor comprising tubing interconnecting a plurality of stations, and means for generating a flow of air along the tubing, the carrier detector comprising means for sensing a differential in the air pressure at a pair of locations within the tubing spaced apart along the axis of the tubing. Brief Description of the Drawings

The invention will further be described by way of example with reference to the accompanying drawing which is a schematic diagram of a carrier detector provided in part of a pneumatic conveyor.

Detailed Description of the Preferred Embodiment

The accompanying drawing illustrates part of a pneumatic conveyor which comprises a plurality of stations (not shown) interconnected by synthetic resin tubing 10 of generally uniform diameter. The conveyor further comprises means for generating a flow of air along the tubing 10. Where it is desired to transport carriers 12 in a single direction only, the means for generating a flow of air within the tubing 10 need only be capable of generating a flow of air in one direction. Where it is desired to transport carriers 12 in either direction along the tubing 10, it is necessary to be able to generate a flow of air along the tubing 10 in both directions.

Carriers 12 for use in the pneumatic conveyor each comprise a generally cylindrical body 14 provided with a pair of circular peripheral seals 16, 18 arranged to provide a sliding seal between the carrier 12 and the inner wall of the tubing 10 receiving the carrier 12. The provision of the seals 16, 18 is important in that it enables a pressure differential to be created along the length of the carrier 12 resulting in the carrier 12 being carried along the tubing 10 by the flow of air through the tubing 10.

In order to provide a signal indicating the passing of a carrier 12 through a particular portion of the tubing 10, a carrier detector 20 is used. The carrier detector 20 comprises a housing 22 divided internally by a diaphragm 36 to define first and second chambers 24, 26. The chamber 24 communicates with the interior of the tubing 10 at a location 30 through a pipe 28, and the chamber 26 communicates with the tubing 10 through a pipe 32 at a location 34 which is downstream of location 30 and is spaced apart therefrom by a distance greater than the length of the carrier 12. Deflection of the diaphragm 36 from a central, rest position effects actuation of an electrical switch, operation of which in use signals the conveyor control system that a carrier has been detected. Movement of the diaphragm 36 may be monitored in a number of ways, for example by a mechanical connection of the diaphragm to the switch. An alternative is to attach a magnet to the diaphragm 36 and monitor change in the magnetic field for example using the Hall effect. When changes in the magnetic field are detected, the switch is operated.

It will be recognised that when the carrier 12 is in the position shown in the drawing, both chambers 24, 26 will be at the same pressure and so the diaphragm 36 will occupy its rest position indicated in the drawing. Movement of the carrier 12 along the tubing 10 towards the detector 20 will not affect this situation until the first seal element 16 of the carrier 12 passes beyond location 30. At this point, the second chamber 26 remains in communication with the interior of the tubing 10 downstream of the carrier 12 whilst the first chamber 24 communicates with the air in the space 38 defined by the outer wall of the carrier 12, the inner wall of the tubing 10 and the seal elements 16, 18. The air pressure in the space 38 is greater than that in front of the carrier 12 by an amount approximately equal to half of the pressure differential between the ends of the carrier 12. The pressure in the chamber 24 thus now exceeds that in the chamber 26 deflecting the diaphragm 36 from its rest position to that shown as a dashed line in the drawing, and so operating the switch to signal the control system that a carrier 12 has been detected adjacent to locations 30, 34.

Further movement of the carrier 12 results in the second seal element 18 passing the location 30. The differential in pressure between the points 30 and 34 is increased, and so if the first pressure differential did not result in the actuation of the switch, the increased pressure differential between the chambers 30 and 34 will.

As the seal element 16 passes beyond the location 34 the pressure differential now detected is that between the pressure in the space 38 and the pressure in the tubing 10 behind the carrier 12. The diaphragm 36 will therefore remain in a deflected position.

Further movement of the carrier 12 results in the second seal element 18 passing the location 34 whereupon both chambers 24, 26 are again subject to the same pressure, the pressure upstream (behind) the carrier 12. The diaphragm 36 thus restores to its rest position reversing operation of the switch and so removing the "carrier detected" signal.

It will be understood that the use of the above mentioned carrier detector enables a signal indicative of the direction of movement of the carrier 12 to be produced if desired, as movement of the carrier 12 in the opposite direction would result in deflection of the diaphragm 36 in the opposite direction from its rest position and such deflection could be used to produce an appropriate signal.

The spacing of the locations 30, 34 preferably exceeds the axial spacing of the seal elements 16, 18 of the carrier 12, but it will be recognised that a functioning detection arrangement can be achieved with lesser spacings. In theory the locations 30, 34 could be spaced by less than the axial thickness of one of the elements 16, 18 but in practice there would be significant disadvantages of such spacing and it is therefore unlikely to be of practical benefit.

Claims

1. A pneumatic conveyor of the type in which a carrier (12) is transported through tubing (10) by an air flow in the tubing, characterized by a carrier detector (20) comprising means (36) for sensing a differential in the air pressure at a pair of locations (30, 34) within the tubing (10) spaced apart along the length of the tubing.

2. A conveyor as claimed in Claim 1, characterized in that the means for sensing said pressure differential comprises an electrical switch and a housing (22) divided by a diaphragm (36) to form first and second chambers (24, 26) said first chamber (24) on one side of the diaphragm (36) communicating with the tubing (10) at one (30) of said pair of locations, said second chamber (26) defined on the other side of the diaphragm (36) communicating with the tubing (10) on at the other (34) of said pair of locations, the switch being arranged to be actuated by movement of the diaphragm (36).

3. A conveyor as claimed in Claim 1 or Claim 2, characterized in that movement of said diaphragm (36) is detected mechanically.

4. A conveyor as claimed in Claim 1 or Claim 2, characterized in that a magnet is attached to the diaphragm (36) and movement of the diaphragm is monitored by monitoring changes in the magnetic field, for example using the Hall effect.

5. A conveyor as claimed in any one of Claims 1 to 4, characterized in that said locations (30, 34) are spaced apart by an amount greater than the axial spacing of the seals of the carrier (12).

6. A carrier detector for use in a pneumatic conveyor characterized by means (22, 24, 26, 36) for sensing a differential in the air pressure at a spaced pair of locations (30, 34) within the tubing (10) of the conveyor.