CA1064457A - Weighing apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Apparatus for weighing a continuous flow of powder material, including two separate weighing hoppers, a diverting valve for switching the flow from one hopper to the other and a closure valve for emptying each hopper.
Each hopper is supported for small vertical movements by a suspension system including two pairs of crossed flexible wires at upper and lower levels, with the intersections of the wires lying on a vertical axis through a load cell which thus senses the gross weight of the hopper and its load. An automatic controller with a register totals the successive recorded gross or live weights of the hoppers and subtracts successive readings of the tare weights.

Description

' 10~4457 This invention relates to weighing apparatus, and is particularly though not exclusively app~icable to the weighing of particulate or powdered solid materials, or fluids, delivered in a continuous, semi-continuous, or intermittent flow or stream. The term "particulate" is not intended to be limitative on the size of the particles, which can range from microus to several inches.
Existlng methods for weighing continuous or semi-continuous flows of material suffer from various disadvantages and are notoriously subject to inaccuracies. For example in the case of continuous belt type conveyors any inaccuracy in the weighing of the belt as it passes over a weighing position is cumulative in the sense that the error is continuously added to the sensed reading. Other mechanical systems involving tipping weighing hoppers are also commonly sub;ect ~
to inaccuracies and other disadvantages due to the somewhat insensitive mechanical weighing systems used and also to the fact that weighing takes place while material is being delivered into the hopper rather than statically, and no proper corrections are applied for the weight of any material "in flight", or retained in the weighing equipment.
Accordingly it is an object of the invention to provide an improved weighing apparatus which will overcome or partly alleviate some of the existing dieadvantages.
This application is a divisional application of Canadian application serial No. 250,207, filed April 13, 1976.

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.~ The invention relates to an apparatus for weighing materials, comprising a hopper with an inlet opening at its upper end, and a controlled outlet opening at its lower end.
Means for supporting the hopper to permit limited vertical ~
movement thereof is provided, comprising an upper flexible :
tension element extending horizontally in one direction from a point on the hopper adjacent the upper end thereof, to a :
fixed point at the same level, and a lower flexible tension element extending horizontally in another generally opposite direction from a point on the hopper adjacent the lower end thereof to a fixed point at the same level. ~here is : .
also provided an electro-mechanical transducer for sensing the weight of the hopper, situated at a position offset . laterally from a vertical line through the centre of the hopper. ~

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Preferably the transducer is of f set to one side of the hopper body or platform. The mounting system as defined above permits this without causing any inaccuracy in the sensed weight and this leaves the upper and lower ends of the hopper clear for flow of the material.
Normally the apparatus will include a pair of flexible tension members at the upper and lower levels and conveniently the two members of one pair extend in non-parallel directions as seen in plan. In this way the two members provide a degree of locating in two orthoganal horizontal directions. Preferably also the two tension members of one or both pairs cross, or intersect extended, adjacent to a point on a vertical line through the transducer-. ' ., ' ' ."

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Such a support system may however ~llow the hopper to rotateor twist within small limits about a vertical axis and the apparatus therefore preferably includes a further horizontal tension member or members arranged to prevent appreciable ' ,, rotary or twisting movements of the hopper about a vertical axi~.
~he,apparatus may also include means for adjusting the effective length of one or each tension member, and/or -the vertical position of one or both ends thereof. '; ' The invention may be performed in various ways and ,, one specific embodiment will now be described by way of example with reference to the accompanying drawings, in which: :
Figure 1 is a somewhat diagrammatic perspective side elevation partly broken away, illustrating a pair of weighing hoppers according to the invention, ~igure 2 is a plan view of the apparatus with the '~
upper inlet structure removed, ~ igure 3 is a schematic diagram illustrating the control system used in conjunction with the twin hopper ~' arrangement Or Figures 1 and 2, and Figure 4 i8 a diagram illustrating the sequence '~;
of steps in a weighing cycle.
Referring first to Figures 1 and 2 the weighing apparatus comprises a main casing 10 of truncated pyramid form, containing two separate weighing hoppers 11, 12. In ::
this example the apparatus is designed to weigh in successive batches a continuous flow of a powdered material such as flour which is 6upplied through a vertical duct 1~ above the apparatus and deli~ered through one or other of two di~charge chutes, 14, 15 controlled by a diverter flap or gate 16 actuated by a pneumatic cylinder 17. ~he individual , . ' ~' .

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10ti4~57 hoppers are each provided with a ~lap or gate valve 20 at the lower end controlled by a pneumatic torque actuator 21.
As seen in plan the upper end of each hopper i8 open and i8 of generally triangular shape with a vertical side 25 and two inclined wall6 26, 27. Shorter intersecting inclined wall~ 28 are located at ths three main corners of the triangle. At the lower end of each hopper the profile quare in plan, represented by the lower ends of the three ~hort walls 28 and the lower narrower part of the ba~e wall 25. Each hopper is ~upported and suspended for small vertical movements solely by a system of horizontal flexible tension members which in this instance are in the form of stranded flexible metal wires, but could alternatively be single-strand wires, flexible straps, cha;ns, diaphragms or pivoted links. Adjacent the upper end of the hopper there are a pair of upper horizontal wires 30, 31 each attached to the hopper body at a point 32 and attached to a fixed part of the ~urrounding casing 10 at a point 33. These two wires 30, 31 extend generally to the left as seen in ~igure 1 but as ~een in plan in Figure 2 they lie generally parallel with the two main sides 26, 27 of the hopper, i.e. 90 (ap~rox.) ,. .
to each other. Adjacent the lower end of the hopper there are a further pair Or lower horizontal tension wires, 34, 35, each of which extends fro~ a point 36 attached to the - hopper bod~ to a point 37 attached to the surrounding fixed hopper casing. The wires 34, ~5 are also at 90 (approx.) each other and the restraint provided by these four flexible tension wires 30, 31, 34, 35 permits the hopper to move within ~mall limits in a vertical direction only, and prevents ; ' or severely limits lateral movement. The ends of the wires - are connected to universal pivsting ~nchorages, which ., : ~ :

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1()~'~45'7 incorporate screw adjustments for varying the tension in the individual wires, and also for setting or varying the effecti~e position of each anchorage.
An electro-mechanical load cell tran~ducer 40 i8 : .
positioned below a projecting plate 41 secured to the hopper body, the load cell being mounted on a rigid platform 42 secured to the surrounding fixed casing 10~ It will be noted that this load cell is offset from a vertical through the centre of the hopper and indeed offset to one side of the whole hopper body. This leave~ the hopper clear for the supply and discharge of the material. ~he load cell is also positioned on a vertical line passing through the point where the two tension wires 30, 31 cros~, and also through the point where the extensions of the two lower tension' wires 34, 35, intersect. Any tilting movement of the hopper about a horizontal axis perpendicular to the paper in a clockwi~e direction as seen in Figure 1 will be resisted b~ the flexible tension wires. On the other hand an~ tendency for the hopper to rotate about the said horizontal axis in an anti-clockwise direction will simply cause the weight of the hopper to be applied to the lo~d cell and the cell itself ~cts as a constraint against such anti-clockwise movement.
~he load cell is thus subject to the to~al gross weight of the hopper including any contents. An~ tendency for the hopper to rotate or twist about a vertical axis is re~trained by a further flexible cross wire 46 which extends horizontall~
parallel with the base wall 25 of the hopper and is anchored at both opposite ends to the surrounding casing 10 and f1xed to a centre point of the wall at an anchorage 47.
Thi~ wire need not be excessively taut and thus provides no restraint on the very small verticul movements of the hopper ' , : . ' : , . . .
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~equire~to actuate the load cell but merely prevent~ the twisting movements referred to.
The apparatu~ also includes a control ~nd recording sy~tem as illustrated in ~igure ~. As shown in this figure the output from the two load cells A and B is fed selectively via a switch 50 to an analogue-to-digital converter 51. This unit may be of known type arranged to convert the voltage si~nals from the load cells to a corresponding variable frequency output and this output is passed through a time controlled gate which thus acts to pass a controlled number of pulses, corresponding to the value of the voltage signal received from the respective load cell. From this unit 51 the pulses are passed to a digital register 52 in the form of an electrical addition/subtraction up-down counter. The counter is arranged to count up, or add, when an input is received on line 53 from a sequence controller 54, and to subtract or count down when a signal is received on line 5j. The sequence controller j4 also controls the switch 50 via a control line 56 and control~ the diverter cylinder 17 via an output 58 and actuates the emptying valve torque unit~
21 via lines 59, 60.
~ he s~quence of operations is illustrated diagramatically in Figure 4. At the instant X at the centre of this figure the controller actuates the diverter unit 1~
to divert the flow Or flour from hopper A to hopper B. After a short interval, when no further flour is entering hopper A, the sequence controller actuates switch 50 to connect load cell A to the converter 51 and emits a signal on line 53 which causes this sensed gross weight signal to be added to the existing total (if any) in the register 52. ~he controller then actuate~ the emptying gate unit 21 to c~use the hopper JWJ/JR - 8 - ' ':

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A to be emptied, after which the controller emit~ a ~ignal on line 55 causing the signal then emitted from the load cell A, corresponding to the tare weight, to be subt~acted from the total on the register 52. The difference between these two figures corresponds closely to the actual quantity of flour discharged from the hopper. ~he controller then again actuates the diverter unit 17 causing the flow of flour to be div~rted back to hopper A~ and shortly afterwards the controller reverses the switch 50 to connect the output of load cell B to the converter 51 and applies a signal to line 5~ causing the signal from the converter, which correspond to the gross live weight Or hopper B, to be added in the register 52. ~he sequence then proceeds as æhown in the left hand part of Figure 4, and i8 repeated indefinitely while the apparatus is in use.
Theoretically, to ~easure the contents discharged from a single hopper it would be necessary to sense the tare weight of the hopper before loading, the gross live weight when charged, and the tare weight when discharged.
In a continuous flow system however the continuous repeating cycle described above is accurate to within very fine limits since the tare weight of the hopper is sensed on each occasion when the hopper is charged and again when it is discharged, and the only theoretical error is the difference between the tare weight at the start of the operation, ~nd the tare weight at the end.
~` It is possible to combine a twin hopper system as illustrated with further multiple twin hopper arrangements to form a compound multiple hopper system, the sequencing controller being arranged to actuate the diverter gates of each hopper system in turn and to perform the sequencing -.
operations as described in turn on all the hoppers of the ~ystem within the total cycle time.
Instead of applying a fixed cycling time the apparatus may be arranged to cycle automatically when the sensed weight of each hopper reaches a predetermined value.
~he apparatuæ can also be operated as a dispensing or batching weigher by pre-setting the required total weight .
into the register and subtracting weighings until the regi~ter reaches zero, at which point the batch is complete.
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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for weighing materials, comprising a hopper with an inlet opening at its upper end, and a controlled outlet opening at its lower end, means for supporting said hopper to permit limited vertical movement thereof, comprising an upper flexible tension element extending horizontally in one direction from a point on the hopper adjacent the upper end thereof, to a fixed point at the same level, and a lower flexible tension element extending horizontally in another generally opposite direction from a point on the hopper adjacent the lower end thereof to a fixed point at the same level, and an electro-mechanical transducer for sensing the weight of the hopper, situated at a position offset laterally from a vertical line through the centre of the hopper.

2. Apparatus according to claim 1, in which said transducer is offset to one side of the hopper.

3. Apparatus according to claim 1, including a further horizontal tension member arranged to prevent or limit rotary or twisting movements of said hopper about a vertical axis.

4. Apparatus according to claim 1, including means for adjusting the effective length of one or each tension member, and/or the vertical position of on or both ends thereof.

5. Apparatus according to claim 1, including a pair of flexible tension members at the upper and lower levels.

6. Apparatus according to claim 5, in which the two members of each pair extend in non-parallel directions as seen in plan.

7. Apparatus according to claim 6, in which the said two tension members of one or both pairs cross, or intersect extended, adjacent to a point on a vertical line through said transducer.