GB2178862A - Weighing apparatus - Google Patents

Abstract

A weighing apparatus, especially but not exclusively for weighing bags in a bag filling apparatus, has a frame (10) for supporting the item (32) to be weighed, the frame being mounted to a support (18) by three equispaced load cells (20) whose axes lie at an angle to the horizontal and to the vertical. <IMAGE>

Description

SPECIFICATION Improvements in or relating to weighing apparatus The present invention concerns improvements in or relating to weighing apparatus, especially but not exclusively weighing apparatus for use in machines for filling large bags and weighing platforms.

There has been proposed in the pasta bag filling machine incorporating a bag weighing arrangement in which a support frame from which the bag is suspended as it is being filled is held by weighing apparatus.

The weighing apparatus has included two load cells but it has been found thatthey have notgiven satisfactorily accurate readings, probably as a result ofthe extraneous stresses built into the machine as a result, for example, ofsupportarrangementsforthe frame.

It is an object ofthe present invention to obviate or mitigate these and other disadvantages.

According to the present invention there is provided a weighing apparatus including a frame for supporting an item to be weighed, the frame being mounted on a rigid support structure by three load cells arranged with their longitudinal axes at an angle to the vertical and horizontal.

Preferablytheframeissuspendedfromthesupport structure by tensile load cells which are preferably mutually equispaced.

Preferably the load cells are arranged at 30 to the vertical.

Preferably the frame is triangular in plan having a load cell pivotally connected to it at each apex.

Preferably the frame carries load support means which may be handles from which a bag to be weighed is suspended or a platform on which a load to be weighed may be supported.

Preferably each cell comprises a plate having pivotal mounting means at each end thereofforfixing to theframe and to the support structure respectively and a reduced thickness centre portion to which is attached at least one strain gauge.

Preferably the meansfor pivotally mounting the plate to the support structure comprises a pin having a reduced diameter centre portion about which the plate is mounted for limited universal movement.

Preferably means are provided on the structure for limiting the movement of the frame relative thereto.

Said means may be upper and lower stops.

Preferably the weighing arrangement is incorporated in a bag filling machine and the frame carries a necksupportforthe bag which is in communication with a hopper discharge valve by way of a flexible connection, for example a fabric stocking.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows purely diagrammatically and not to scale a plan view of a weighing apparatus incorporated in a bag filling machine; and Figure2shows a diagrammatic partial elevation of the apparatus.

Figure3is a sectional plan on the line Ill-Ill of Figure 4ofa modified load cell and its mounting means; and Figure4 is an elevation of the modification.

A bag weighing apparatus comprises a triangular frame 10 having two bag support handles 12 fixed to two of its sides and a necksupport assembly 14 mounted in its centre by spiders 16. The frame is suspended from a support structure 18 (Figure 2) by three load cells 20 only one of which is shown in detail in Figure 1. Each load cell is pivotally mounted to the frame and to the support structure and is arranged with its axis at 30' to the vertical. Each load cell is a rectangular plate having mounting holes 22 at each end thereof.The width of the plate is reduced between its ends such that it has a substantially I-shape and strain gauge 24 is fixed to the reduced width portion in known manner, the electrical leads 26 from the strain gauge being connected to a signalling and computing arrangement which summatesthesignals from the gauges and displays a reading of the weight carried bytheframe.

The enlarged portion of Figure 2 shows a support structure pin 28 about which the load cell 20 is universally pivotally mounted. The pin 28 has a diameter which is slightly greater than the diameterofthe hole 22 in the plate 20 but to allowforthe required universal pivotal movementofthe plate 20 about the pin 28 it has a waisted portion 30 of reduced diameter.

From Figure 2 it can be observed that a bag 32 to be filled is supported by its handles 34 with the neck 36 of the bag being held by the neck support ring 14. The bag is filled with fluent material, for example powder, from a storage hopper (not shown) by means of a valve (not shown) which discharges into a nozzle 38 which communicates with the neck assembly 14 by means of a flexible nylon stocking 40.

The connection ofthe load cells 20to theframe 10 has not been shown in detail but it will be realisedthat this connection should be a universal pivotal connection similarto that shown in the detail of Figure 2 so that movement of the frame, for example tipping movement relative to the support structure 18, does not induce any stresses in the load cell such that the signals given out by the strain gauge are proportional directly to the load applied by way of the handles 12.

To prevent excess tipping movement of the frame due, forexample, to uneven loading ortofracture of one of the loadcells the support structure 18 is provided with upper and lower stop means which may take any convenient form but which are illustrated in Figure 2 as upper and lower abutment members 42, 44 respectively.

Various modifications can be made without departing from the scope of the invention, for examplethe support structure can take any convenient form and the pivotal mounting of the load cells to the frame and supportstructure may be varied provided that univer- sal movement within the operating range can be achieved. The load cell may be modified,forexample, it could comprise a circular cross-section bar having a reduced diameter central portion. More than one strain gauge may be used in each cell.

In the modified arrangement shown in Figures 3 and 4 (wherein equivalent components to those shown in Figures 1 and 2 have geen given the same reference numerals) the load cells are arranged in a plane which intersects the apices oftheframe lOon pins 28 whose axes are horizontal. Figure 3 shows thatthe pivotal connection ofthe cell 20 to the frame 10 is similarto that described with reference to Figure 2, that is by a pin 28 having a waisted central portion around which the cell is mounted. The mounting holes 22 in the cell have a d iameter su bstantial Iy equal to the diameter of the pin. The ends of each pin are mounted in lugs on the frame andsupportandare held in position by split pins.In this modification the upper and lower stops 42,44 are pins fitted in the support structure 18 above and below an extension piece 43 of the frame 10.

In a further modification the frame loins modified such that it provides a platform on which loads to be weighed can be supported. In other words the appar- atus serves as a weighing platform. In the weighing platform modification the load platform may be suspended from a central plinth, from which it overhangs, bythreeloadcellswhoseupperendsare arranged inwards of their lower ends.

In a further modification the load cells may be mod fixed to give load readings by sensing and signalling the shearforces therein, ratherthan the tensile forces described above. Similarly, with suitable structural modification compressive forces in the load cells could be sensed.

Claims (13)

1. Aweighingapparatus including aframefor supporting an item to be weighed, the frame being mounted on a rigid support structure bythree load cells arranged with their longitudinal axes at an angle to the vertical and horizontal.

2. Aweighing apparatus as claimed in claim 1,in which the frame is suspended from the support structure by tensile load cells which are preferably mutual- ly equispaced.

3. Aweighing apparatus as claimed in claim 1 or claim 2, in which the load cells are arranged at30 to the vertical.

4. Aweighing apparatus as claimed in any one of claims 1 to 3, in which the frame is triangular in plan having a load cell pivotally connected to it at each apex.

5. Aweighing apparatus as claimed in any one of the preceding claims, in which the frame carries load support means from which a load to be weighed is suspended.

6. Aweighing apparatus as claimed in any one of claims 2to 5, in which each cell comprises a plate having pivotal mounting means at each end thereof forfixing to theframe andto the support structure respectively and a reduced thickness centre portion to which is attached at least one strain gauge.

7. Aweighing apparatus as claimed in claim 6, in which the meansfor pivotally mountingthe plateto the support structure comprises a pin having are duced diameter centre portion about which the plate is mounted for limited universal movement.

8. Aweighing apparatus as claimed in any one of the preceding claims, in which means are provided on the structure for limiting the movement of the frame relative thereto.

9. Aweighing apparatus as claimed in claim 8, in which said movement limiting means are upper and lower stops.

10. A bag filling machine incorporating a weighing arrangement as claimed in any one of the preceding claims, in which the frame carries a neck supportforthe bag which is in communication with a hopperdischargevalve byway of a flexible connec- tion.

11. Aweighing apparatussubstantiallyas hereinbefore described with reference to the accompanying drawings.

12. A bag filling machine substantially as hereinb- efore described with reference to the accompanying drawings.

13. Any novel subject matter or combination including novel subject matter disclosed in the foregoing specification or claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding claims.