GB2215476A

GB2215476A - Apparatus for weighing a sample of a product

Info

Publication number: GB2215476A
Application number: GB8804866A
Authority: GB
Inventors: Anthony Raymond Varnde Roberts
Original assignee: C I ELECTRONICS Ltd
Current assignee: C I ELECTRONICS Ltd
Priority date: 1988-03-01
Filing date: 1988-03-01
Publication date: 1989-09-20
Also published as: GB8804866D0

Abstract

Apparatus for use in weighing a sample of a product 11 e.g. a capsule or tablet being discharged from a machine (10) comprises a sample weight unit (16) and an electronic weight display/control unit (17) adjustably mounted on a stand (15), the weighing unit (16) comprising an electronic weighing balance (30) having a weighing pan (27) to which a sample of product (11) is conveyed by a pulse of compressed air from a device (19) actuated by a detector (18) which moves the sample product (11) into a venturi device (22) which also receives a pulse of compressed air through an orifice (25) to entrain air to flow through the venturi device (22) to convey the sample product (11) to the pan (27), the sample product being guided along its path by a perforated wall (26) through which the conveying air flows to atmosphere, and the sample product (11) after being weighed is removed from the pan (27) by a pulse of compressed air supplied through a nozzle (31) and it then falls by gravity through the inoperative venturi (22) back to the flow of product (11) being discharged from the machine (10). <IMAGE>

Description

APPARATUS FOR WEIGHING A SAMPLE OF A PRODUCT This invention relates to apparatus for use in weighing a sample of a product produced in a machine.

Machines used for manufacturing pharmaceutical products such as tablets and capsules usually operate at high speed and it is necessary to control the weight of the product within a narrow range to meet the tolerance imposed by statutory regulations.

The known methods of manual sampling and weight checking are time consuming and wasteful of product, as the sample after weighing is discarded due to possible contamination.

Some tablet-producing machines incorporate means for diverting a sample of the product to an external weighing device or co-relate the main weight of product to a continuous measurement of punch pressure.

According to the present invention there is provided apparatus for use in weighing a sample of a product produced in a machine, comprising air operated means for extracting a sample from a flow of product and conveying the sample to a weighing means, air-operated means for removing the weighed sample from the weighing means and means for conveying the removed weighed sample back to the product flow discharged from the machine.

An embodiment of the invention will now be described, by way of an example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic perspective view of a tablet-compressing machine provided with apparatus for weighing a sample in accordance with the present invention; and Figure 2 is a vertical section through the apparatus for weighing a sample.

The machine 10 is a tablet-compression machine for producing tablets 11 which are discharged from the machine along an exit or discharge chute 12 in uniformly spaced apart relationship, the spacing being dependent on the speed of the machine. The discharged tablets 11 are collected in a container *3. Alternatively, the machine 12 may be a izapsu.e-forr-iing machine.

Located adjacent to the machine 10 is a sample-weighing apparatus 14 embodying the present invention. The apparatus 14 comprises a stand 15 which supports a sample-weighing unit 16 and an electronic control and weight display unit 17.

The sample-weighing unit 16 is located adjacent to the discharge chute 12 and comprises an optical detector 18 having a light beam for detecting a tablet or capsule 11, a transverse orifice 19 from which a pulsed compressed air stream can be discharged for deflecting a sample tablet or capsule 11 into the inlet aperture 20 of an air mover 21. The pulse of compressed air is triggered by the optical detector 18. The air mover 21 consists of a venturi device 22 having an air inlet port 23 which communicates with an annular chamber 24 and which has an annular orifice 25 located at the throat of the venturi device 22.A pulse of compressed air is applied to the inlet port 23 and this air flows through the chamber 24 and out of the orifice 25 when it entrains a much larger volume of air through the inlet aperture 20, carrying with it a sample tablet or capsule 11 directed towards the inlet aperture 20 by the air stream pulsed through the orifice 19.

Aligned with the downstream edge of the venturi device 22 is a curved wall formed by a mesh 26. The mesh 26 may be formed of glassfibre-reinforced plastics material or stainless steel. The sample tablet or capsule 11 follows a trajectory guided by the mesh 26 which directs it to a weighing pan 27. The mesh 26 allows a large proportion of the air stream to pass therethrough into an expansion chamber 28 formed within a cover 29.

The air is exhausted to atmosphere through a filter (not shown) to prevent dust being carried into the atmosphere.

The weighing pan 27 forms part of an electronic balance 30 which converts the weight of the sample tablet or capsule 11 into a digital signal which is displayed on the electronic control and weight display unit 17. The unit 17 may automatically adjust the machine 10 or other processing equipment to maintain a desired mean weight of product, or data on the sample weight can be displayed for action by the machine operator.

After being weighed, the sample table or capsule 11 is ejected from the weighing pan 27 by an air jet supplied through a nozzle 31, which causes the sample tablet or capsule 11 to follow a trajectory indicated by broken line 32 back through the air mover 21 to rejoin the stream of tablets or capsules 11 being discharged from the chute 12.

All parts of the sample-weighing unit 16 which are contacted by the sample tablet or capsule 11 are formed of suitable materials which can be easily cleaned. The metallic parts are preferably formed of stainless steel or anodised aluminium. Preferably the mesh 26 is non-metallic to prevent damage to samples and may be disposable.

The weighing apparatus is designed to provide minimal interferance with the normal operation of the tablet or capsule-producing machine 10 and minimal interferance with the placement of containers 13 for collecting the product. The sampling and weighing unit 16 is adjustably mounted on the stand 15 and the axial distance which the unit 16 occupies beyond the end of the chute 12 is preferably no greater than 50 mm.

Preferably the air flows are pulsed by solenoid valves.

An initial lift is imparted to the sample tablet or capsule 11 by having the air jet mounted below its line of movement directed towards the orifice 25 of the venturi device 22.

The air flow which carries the sample tablet or capsule 11 is diverted away from the weighing pan 27 through the mesh 26 so as to permit accurate weighing of the sample.

The weighing unit 30 is preferably a top-pan force balance which can weigh with a precision of say 1 mg on a 2 gm capacity.

The sample removed from the weighing pan 27 by the air jet 31 falls by gravity back through the inoperative air mover 21.

Claims

1. Apparatus for use in weighing a sample product produced in a machine, comprising a sample weighing means, air-operated means for extracting a sample from a flow of product and for conveying the sample to said weighing means, air-operated means for removing the weighed sample from the weighing means, and means for conveying the removed weighed sample back to the product flow being discharged from the machine.

2. Apparatus as claimed in claim 1, in which the air-operated means for extracting a sample and for conveying the sample to said weighing means comprises detecting means for detecting the presence of a sample being discharged from the machine, means operated in response to the detecting means for producing a pulse of compressed air for moving the sample from said flow of product into the apparatus, a venturi device into which the removed sample is received, means for producing a pulse of compressed air in the venturi device to entrain into the venturi device a flow of air for conveying the sample through the venturi device to the weighing means, and a porous guide wall for guiding the conveyed sample to said weighing means.

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3. Apparatus as claimed in claim 2, in which the porous wall is formed by a mesh through which the conveying air can flow to atmosphere through an expansion chamber.

4. Apparatus as claimed in claim 3, in which the mesh is formed of glass-fibre reinforced plastics material or stainless steel.

5. Apparatus as claimed in claim 3 or claim 4, in which the conveying air is exhausted to atmosphere through a filter.

6. Apparatus as claimed in any one of claims 2 to 5, in which said porous wall is curved.

7. Apparatus as claimed in any one of claims 2 to 6, in which the means for discharging the pulse of compressed air for moving a sample into the apparatus is located below the line of movement of the sample towards the apparatus so as to impart an initial lift to the sample.

8. Apparatus as claimed in any preceding claim, in which the airoperated means for removing the weighed sample from the weighing means comprises means for producing a pulse of compressed air to remove the weighed sample.

9. Apparatus as claimed in any preceding claim, in which the weighing means comprises an electronic balance having a weighing pan and a weight display/control unit.

10. Apparatus as claimed in claim 9, in which the conveying air flow is diverted away from the weighing pan.

11. Apparatus as claimed in claim 9 or claim 10, in which the weight display/control unit is arranged to automatically adjust the machine or other processing equipment to maintain a desired mean weight of product.

12. Apparatus as claimed in any preceding claim adjustably mounted on a stand.

13. Apparatus for use in weighing a sample product produced in a machine, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.