GB2026176A - Weighing method and apparatus - Google Patents

Abstract

The mass of articles (13) is determined by feeding them from a feed station (10) to impact a cantilevered spring arm (18) at a weighing station (12) with a common velocity. A transducer (24) provides a signal representative of the momentum of the article on impact with a plate (20) on the arm (18). The signal may be used to provide an absolute or comparative resolution of mass. The mass may be related with a characteristic of the articles, such as radioactivity measured at radiation counters (28), to generate a mass-to- characteristic ratio. The articles can then be graded according to this ratio. The common velocity of the articles can be generated by free fall under gravity or by imparting a significant forward velocity from a conveyor. <IMAGE>

Description

SPECIFICATION Weighing apparatus and method This invention relates to a method of weighing and sorting articles according to their mass or a mass to other characteristic ratio and to apparatus for carrying out the method.

A method of weighing articles according to the invention includes the steps of causing the articles to move at a common velocity; measuring the momentum of the articles and computing the momentum of each article with the velocity to determine its mass or its mass relative to another article.

Preferably, the momentum of the articles is determined by measuring the deflections, velocities or accelerations of a member impacted by the articles.

In one form of the invention the method includes the step of causing the articles to move at a known velocity by allowing the articles to fall a fixed distance under gravity on to the movable member.

In another form the articles can be projected forwardly to impact a movable member.

Further according to the invention the method includes the steps of measuring a characteristic of each article and computing the mass of the article and its measured characteristic to arrive at a mass to characteristic ratio for each article. The measured characteristic of each article may be its radio active radiation which is measured by means of a scintillation counter. The scintillation counter is conveniently located adjacent the path along which the articles fall onto the movable member.

Still further according to the invention the method includes the step of sorting the weighed articles into articles having a mass or mass to characteristic ratio above a predetermined level from those below the predetermined level. The sorting may be accomplished by means of air jets which are directed onto the articles at the weighing station.

Weighing apparatus according to the invention includes means for feeding articles sequentially and at a common velocity to a weighing station, means at the weighing station to measure the momentum of articles arriving at the station and means for computing the momentum of each article with its velocity to determine their mass or their mass relative to another article.

The article feed means may consist of a conveyor having a discharge position which is located at a fixed distance above the weighing station and which is adapted to drop the articles singly under gravity to the weighing station, or a conveyor moving at a substantial, but constant, speed to project the articles forwardly at that speed.

Further according to the invention the weighing station includes a movable member which is positioned to be impacted by articles from the article feed means, and means connected to the movable member for generating a signal proportional to the movement of the movable member when impacted by an article. The movable member is conveniently mounted for resilient movement on a spring and the signal generator may be an electro mechanical transducer for generating an electrical signal proportional to the degree of deflection of the movable member or the velocity of the movable member, of the time integral of the velocity.

In a preferred form of the invention the apparatus includes means for measuring a characteristic of each article and means connected to the characteristic measuring means and weighing station for determining a mass to characteristic ratio for each article. The characteristic measuring means is preferably a scintillation counter for measuring the radio active radiation of each article but could equally well be an arrangement for measuring another characteristic of the articles such as their reflectivity, colour or fluorescence.

Still further according to the invention the apparatus includes means at the weighing station for sorting articles having a mass or mass to characteristic ratio above a predetermined level from those below the predetermined level. The sorting means may be at least one device having means for directing an air jet at the articles to deflect them from the weighing station in one direction or another in dependence on their mass or mass to characteristic ratio relative to a reference.

An embodiment of the invention is now described by way of example with reference to the drawing which is a diagrammatic fragmentary side elevation of the weighing apparatus of the invention.

Detailed description of the preferred embodiment The drawing shows the apparatus of the invention to include an article feeder station indicated generally at 10, and an article weighing station indicated generally at 12.

The feeder station 10 in this embodiment of the invention is a conveyor 14 which may be either a belt or vibrator conveyor along which particles 13 of mined ore fed from a hopper, not shown, which is adapted to deposit the articles singly onto the conveyor.

The weighing station 12 includes a frame 16 which carries a cantilever spring 18 which in turn carries a fixed plate 20. Movement of the spring 18 is damped by a pneumatic or hydraulic dash pot arrangement 22. An electro mechanical transducer 24 is connected between the frame 16 and spring 18 to provide an electrical signal which is proportional to the degree of spring deflection or velocity or time integral of velocity and which is fed to a computer 26.

The free end of the conveyor 14 is so positioned above the plate 20 of the weighing station that particles of ore which fall from the conveyor will land on the plate. Higher speed operation can be achieved if the plate 20 is vertical or has a substantial vertical component and the conveyor 14 moves at a substantial speed so that the particles 13 have a substantial component of constant horizontal velocity.

As the discharge end of the conveyor is located a fixed distance above the plate 20 the ore particles will strike the plate 20 at, for all practical purposes, a constant common velocity. The force/time required for the plate 20 to arrest the momentum of each particle against the bias of the spring is, when computed against the known velocity of the particle, proportional to the mass of the particle.

The weighing only of the particles 13 could be employed to achieve a number of ends. For example, counting together with weighing could be used to resolve mass flow in unit time.

With ores having a radio active component the apparatus includes scintillation counters 28 which are suitably lead shielded and located adjacent the flight path of the particles between the feeder 12 and plate 20. The counters 28 are connected to the computer 26 so that a mass to radiation measurement may be made of each particle. The particles may then be segregated or sorted into a fraction having a mass to radio activity ratio above a predetermined level and a fraction below that level.

The sorting of the particles 13 could be accomplished by means of devices, not shown in the drawing, which are controlled by the computer and adapted to provide air jets to deflect the particles, when weighed, in one direction or another in dependence on their mass to radio activity ratio. The particles could be deflected by the air jets from the plate 20 onto either of two or more conveyors located adjacent the weighing station.

The discharge of the articles from the conveyor 14 could be regulated by a signal from the transducer 24.

The invention is not limited to the precise constructional details as herein described and the spring 18 could, for example, be replaced by a coil spring, a diaphragm or an air spring. The invention may further employ, in place of the scintillation detectors 28 for the radio active measurement of the particles 13, means for measuring another characteristic of the particles such as their reflectivity, colour or fluorescence to arrive at a desired mass to characteristic ratio. The absolute measurement of parameters of the particular may not always be necessary. A comparative measurement may be arranged.

Claims (25)

1. A method of weighing articles including the steps of causing the articles to move at a known or common velocity, measuring the momentum of the articles and computing the momentum of each article with the velocity to determine its mass or its mass relative to another article.

2. A method as claimed in Claim 1 in which the momentum of each article is measured by measuring the deflection of a movable member impacted by the article.

3. A method as claimed in Claim 1 in which the momentum of each article is measured by measuring the velocity of a movable member impacted by - the article.

4. A method as claimed in Claim 1 in which the momentum of each article is measured by measuring the acceleration of a movable member impacted by the article.

5. A method as claimed in any one of Claims 2 to 4 including the step of causing the articles to move at a known or common velocity by allowing the articles to fall a fixed distance under gravity onto the movable member.

6. A method as claimed in any one of Claims 2 to 4 including the step of causing the articles to move at a known or common velocity by projecting the articles to travel forwardly a fixed distance to impact the movable member.

7. A method as claimed in any one of the above claims including the step of measuring a characteristic of each article and computing the mass of the article and its measured characteristic to arrive at a mass to characteristic ratio for each article or relative to other articles.

8. A method as claimed in Claim 7 in which the measured characteristic of each article is its radio active radiation.

9. A method as claimed in Claim 5 in which the measured characteristic of each article is its radio active radiation which is measured by means of a scintillation counter which is located adjacent the path along which the articles fall onto the movable member.

10. A method as claimed in any one of the above claims including the step of sorting the weighed articles into articles having a mass or mass to characteristic ratio above a predetermined level for those below the predetermined level.

11. A method as claimed in Claim 10 including the step of sorting the articles by means of air jets.

12. Weighing apparatus including aweighing station, means for feeding articles sequentially and at a common velocity to the weighing station, means at the weighing station to measure the momentum of articles arriving atthe station and means for computing the momentum of each article with its velocity to determine their mass, or their mass relative to another article.

13. Apparatus as claimed in Claim 12 in which the article feed means is a conveyor having a discharge position which is located at a fixed distance above the weighing station and which is adapted to drop the articles singly under gravity to the weighing station.

14. Apparatus as claimed in Claim 12 in which the article feed means projects the articles forwardly to the weighing station.

15. Apparatus as claimed in either one of Claims 12 to 14 in which the weighing station includes a movable member which is positioned to be impacted by articles from the article feed means, and means connected to the movable member for generating a signal proportional to the movement of the movable member when impacted by an article.

16. Apparatus as claimed in Claim 15 in which the movable member is mounted for resilient movement on a spring.

17. Apparatus as claimed in either one of Claims 15 to 16 in which the signal generator is an electro mechanical transducer for generating an electrical signal proportional to the degree of deflection of the movable member, or the velocity of the movable member, or the time integral of the velocity.

18. Apparatus as claimed in any one of Claims 12 to 17 including means for measuring a characteristic of each article and means connected to the characteristic measuring means and weighing station for determining a mass to characteristic ratio for each article, or a mass to characteristic ratio relative to other articles.

19. Apparatus as claimed in Claim 18 in which the characteristic measuring means is a scintillation counter for measuring the radio active radiation of each article.

20. Apparatus as claimed in any one of Claims 12 to 19 including means at the weighing station for sorting articles having a mass or mass to characteristic ratio above a predetermined level from those below the predetermined level.

21. Apparatus as claimed in Claim 20 in which the sorting means is at least one device having means for directing an air jet at the articles to deflect them from the weighing station in one direction or another in dependence on their mass or mass to characteristic ratio relative to a reference.

22. A method of weighing articles substantially as herein described.

23. A method of sorting articles substantially as herein described.

24. Weighing apparatus for weighing articles substantially as herein described with reference to the accompanying drawing.

25. Apparatus for sorting articles substantially as herein described with reference to the accompanying drawing.