GB2470003A

GB2470003A - A quantitative powder dispensing system

Info

Publication number: GB2470003A
Application number: GB0907585A
Authority: GB
Inventors: Andrew Whitwell
Original assignee: LABMAN AUTOMATION Ltd
Current assignee: LABMAN AUTOMATION Ltd
Priority date: 2009-05-05
Filing date: 2009-05-05
Publication date: 2010-11-10
Also published as: GB0907585D0

Abstract

The invention relates to system for dispensing specific quantities or doses of a powdered or pulverulent material. It comprises a hopper 10 having a dispensing outlet 11 and a vibration means 20 is attached to the hopper 10. A receptacle 40 receives dispensed powder from the hopper 10. A motorised shutter 30 is disposed between the dispensing outlet and the receptacle whereby the motorised shutter is moveable between a position in which the dispensing outlet is fully closed and a position in which it is fully open. An electronic balance 50 operatively engages with the receptacle and is connected to a control unit 80 which is also connected to the vibration means, the motorised shutter and the electronic balance means 50 so that the amount of dispensed material may be controlled.

Description

A Quantitative Powder Dispensing System This invention relates to a dispensing system for powdered and pulverulent materials.

In particular, the invention relates to the accurate dispensing of a specific quantity of a powder.

Powders, for example chemical materials or pharmaceutical ingredients, are often required in very specific measured quantities. The quantity of powder required is often a specific weight within a very tight tolerance: of the order of � 0.00 1g. For some powders, the average particle may have a mass close to, or greater than, this magnitude.

Conventional techniques for measuring the quantity of a dispensed powder have employed a pepper-grinder type dispenser or, as shown in Figure 1, a hopper and an auger configuration.

Referring to Figure 1, a conventional dispensing system includes a hopper I for receiving and dispensing powder 8. The hopper 1 includes a rotatable auger 2 and a baffle 3.

Powder is introduced at the top of the hopper 6 and exits 7 passed the baffle 3 into a receptacle 4. A balance 5 weighs the receptacle 4 and its powder contents 8.

However, a problem arises with this arrangement in that powder particles with a size greater than the opening 9 become lodged between the hopper 1 and baffle 3 causing a blockage. Also, powder particles cluster into groups, which severely limits the possibility of dispensing powder particle by particle.

Another conventional powder feeding system incorporates an auger in a horizontal position without a baffle arrangement.

An object of the present invention is to provide an improved dispensing system that addresses the problems associated with particle sizes and powder blockage.

According to an aspect of the present invention there is provided a quantitative powder dispensing system comprising: a hopper having a dispensing outlet; a vibration means attached to said hopper; a receptacle for receiving dispensed powder from said hopper; a motorised shutter disposed between said dispensing outlet and said receptacle, the motorised shutter moveabte between a position in which said dispensing outlet is fully closed and a position in which said dispensing outlet is fully open; an electronic balance means operatively engaged with said receptacle; and a system control unit interconnected between said vibration means, said motorised shutter, and said electronic balance means.

In a preferred embodiment, the motorised shutter comprises a disc having an off-centre axis of rotation. In another embodiment, the shutter comprises a slider-plate.

Preferably, the motorised shutter includes an aperture, which may be a circular opening, a V-shaped slot, or a substantially crescent-shaped slot.

In a preferred embodiment, the shutter is motorised via a servomotor. Alternatively, a stepper motor may drive the shutter.

Preferably, the vibration means comprises a vibromotor. Alternatively, in addition to a vibromotor, the vibration means may include an offset weight.

In an alternative embodiment, the vibration means comprises a pneumatic vibration device or an acoustic vibration device.

According to another aspect of the present invention there is provided a method of quantitatively dispensing powder from a hopper comprising: providing vibration means for vibrating the powder; providing a motorised shutter between a dispensing outlet of the hopper and a receptacle for receiving dispensed powder; providing an electronic balance means for weighing the dispensed powder in the receptacle; providing a system control unit connected to the vibrating means, the motorised shutter, and the electronic balance means; opening and closing the dispensing outlet via the motorised shutter in response to a control loop feedback mechanism. /

Preferably, the control loop feedback mechanism is controlled via an iterative algorithm. The algorithm may be stored in the system control unit or any alternative device that is in communication with the system control unit, for example a personal computer temiinal.

In a preferred embodiment, the iterative algorithm utilises frizzy logic. Alternatively, the iterative algorithm is a proportional integral derivative (PD) algorithm.

Preferably, the iterative algorithm operates on five variable parameters: target weight of the dispensed powder; maximum flow rate of powder output through the dispensing outlet; tolerance of the target weight; error factor; and flow factor.

According to a further aspect of the present invention there is provided a method of quantitatively dispensing powder comprising the steps of: agitating the powder within a powder container; dispensing the powder through a shuttered aperture into an electronic balance weighing receptacle; wherein the aperture size is varied by operation of a shutter mechanism in response to feedback from the electronic balance.

Embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying schematic drawings, in which: Figure 1 shows a prior art system of dispensing a measured amount of powder; Figure 2 shows an embodiment of the quantitative powder dispensing system of the present invention; Figure 3 shows a detail of art embodiment of a motorised shutter and hopper assembly of the present invention; Figures 4A to 4C show underside views of a shutter progressively covering a dispensing outlet; Figure 5 shows a detail of an alternative embodiment of a motorised shutter and hopper assembly of the present invention; Figure 6 shows a shutter comprising a slider plate with a V-shaped slot; and Figure 7 shows a shutter including a substantially crescent-shaped slot.

With reference to Figure 2, a quantitative powder dispensing system comprises a hopper 10 containing a powder (not shown), the hopper 10 is held upright in a support structure 60. A vibromotor 20 is attached to the external structure of the hopper 10 and provides vibrational agitation of the powder contained within the hopper 10.

As an alternative to the vibromotor, powder agitation can be achieved by the use of either a pneumatic or an acoustic vibrational device.

Beneath the hopper 10, and supported by the support structure 60, is a shutter 30, and below this a receptacle 40 sits atop an electronic balance 50. The shutter 30 is connected to, and driven by, a servomotor 70.

The electronic balance 50 is connected to an electronic balance control unit 55, which is in turn connected to a system control unit 80. As can be seen from Figure 2, the vibromotor 20 and the servomotor 70 are also connected to the system control unit 80.

In operation, the system control unit 80 accesses a database in which powder data is stored. This data comprises the identification of the powder to be weighed, the target weight of powder to be dispensed, the tolerance of the target weight, the maximum flow rate of the powder, the flow factor, and the error factor. in addition to this, the database also holds a flag to indicate the next powder to be dispensed and data related to all previous dispensing operations.

A reservoir of powder is held in the hopper 10 and powder is dispensed from a hopper outlet 11 (not shown in Figure 2) by operation of the shutter 30, the dispensed powder being received in the receptacle 40. To assist the flow of the powder, and to avoid blockages occurring at the hopper outlet 11, the vibromotor 20 imparts vibration to the hopper 10 that in turn agitates the powder held within.

S

During a dispensing operation, the extent to which the hopper outlet 11 is exposed to allow throughput of powder is determined by the relative position of the shutter 30.

The shutter 30 can be disposed in any position between that which exposes the entire hopper outlet 11 to the receptacle 40, and that in which the hopper outlet 11 is entirely closed-off to the receptacle 40. The relative position of the shutter 30 with respect to the hopper outlet 11 is detennined by operation of the servomotor 70.

The system control unit 80 incorporates a memory unit and a processor for storing and executing an iterative feedback algorithm that varies the exposure size of the hopper outlet in real time during a dispensing operation. The system control unit 80 also includes a vibromotor system control unit, for example a relay, for controlling the operation of the vibromotor, and a communications interface enabling connection to, and communication with, an external computer or communications network.

The system control unit 80 is connected to the electronic balance control unit 55.

During a dispensing operation the system control unit 80 can calculate the precise weight of powder present in the receptacle 40 at any given instant. In actual operation, the weight of powder in the receptacle is being constantly updated; this information is processed by the iterative feedback algorithm enabling real-time adjustment of the extent to which the hopper outlet Ii is exposed to the receptacle 40.

In a typical operation, the hopper outlet 11 will initially be fully exposed to allow a fast flow rate of powder into the receptacle 40. As the target powder weight is neared, the system control unit 80, in response to iterative feedback data, responds by reducing the exposure of the hopper outlet 11 to the receptacle 40 via actuation of the servomotor 70. This process is repeated continuously until the weight of powder in the receptacle 40 is within the tolerance of the target weight, e.g. Target Weight [g] � tolerance [g].

An algorithm, preferably stored in the system control unit 80, processes iterative feedback data. However, it should be noted that since the control unit 80 includes a communications interface (not shown), the feedback algorithm could be stored at other locations. For example, the algorithm may be stored on a personal computer It connected to the control unit 80, or it may be located on a remote server and be accessible through a network.

In a preferred embodiment, the algorithm used is based on frizzy logic. Alternatively, a proportional integral derivative (P11)) algorithm can also be employed.

The algorithm is executed on the basis of five system variables: * the predetermined target weight of the powder to be dispensed * the maximum flow rate of powder from the hopper (i.e. when the outlet is frilly exposed) * the allowed tolerance of the target weight * error factor(s) * flow factor(s) During the dispensing process it is vital that the powder contents of the hopper 10 are continually agitated so that particles of a size less than that of the currently exposed size of the hopper outlet are able to migrate towards, and ultimately flow out of, the hopper outlet. In this way, the system can actively home-in' on the desired weight of powder, and no individual powder particles can become stuck in the hopper outlet causing a blockage.

Referring now to Figure 3. Here, an embodiment of a motorised shutter and hopper assembly is shown in isolation from the overall system.

In this embodiment, the shutter 30 comprises a circular disc 31 rotatable by the servomotor about an off-centre axis 32. The hopper 10 comprises a powder canister 12 arid feeder section 13. The feeder section 13 includes a hopper outlet 11 (shown as a broken-line tube).

Figure 3 is not drawn to scale, but in practice it has been found that the hopper outlet 11 has an optimal size of between 1 and 2mm in length, and a diameter of 10mm.

The powder canister 12 is secured to the feeder section via a screw thread 14. An ideuitical screw thread 14' enables a lid 15 to be secured in place as shown. In practice, the canister 12 can be used either way up, since the threads 14 and 14' are the same.

Once the canister 12 has been charged with powder and, if necessary the lid 15 has been secured in place, dispensing can commence.

Referring now to Figures 4A to 4C. Figure 4A shows, from an underside view, the circular disc 31 in a position where the hopper outlet 11 is fully exposed. Figure 4B shows the same view as Figure 4A after a partial turn of the circular disc 31 about the off-centre axis 32. Here, the hopper outlet 11 is partially obscured. Consequently, the size of particle that can be dispensed has been reduced. Further rotation of the circular disc 13, as shown in Figure 4C, leads to the hopper outlet 11 being totally obscured, thus terminating further powder output.

An alternative embodiment of a motorised shutter and hopper assembly is shown in Figure 5. Here, the shutter 30 comprises a slider-plate 33 driven reciprocally by the servomotor 70. The slider-plate includes a V-shaped slot (see Figure 6) axially aligned with a diameter of the hopper outlet 11. Left to right movement of the slider plate (as viewed in Figure 6) increases the extent to which the hopper outlet 11 is exposed and, conversely, right to left movement reduces the exposure of the hopper outlet Il.

As an alternative to the circular disc 31, and as shown in Figure 7, the shutter 30 includes a circular disc 35 that incorporates a substantially crescent-shaped slot 36. In contrast to the circular disc 31 as shown in Figures 3,and 4A to 4C, the circular disc is rotated about the geometric centre 37 of the disc by the servomotor 70. Here, since diverging waIls delineate the slot, movement between a fully closed and a fully open hopper outlet is achieved by rotation about the actual centre of the disc.

Claims

Claims 1. A quantitative powder dispensing system comprising: a hopper having a dispensing outlet; a vibration means attached to said hopper; a receptacle for receiving dispensed powder from said hopper; a motorised shutter disposed between said dispensing outlet and said receptacle, the motorised shutter moveable between a position in which said dispensing outlet is fully closed and a position in which said dispensing outlet is fully open; an electronic balance means operatively engaged with said receptacle; and a system control unit interconnected between said vibration means, said motorised shutter, and said electronic balance means.
2. A quantitative powder dispensing system as claimed in claim 1, wherein the motorised shutter comprises a circular disc.
3. A quantitative powder dispensing system as claimed in claim 2, wherein the circular disc has an off-centre axis of rotation.
4. A quantitative powder dispensing system as claimed in claim 1, wherein the shutter comprises a slider-plate.
5. A quantitative powder dispensing system as claimed in claim 2 or 4, wherein the motorised shutter includes an aperture.
6. A quantitative powder dispensing system as claimed in claim 5, wherein the aperture is a V-shaped slot or a substantially crescent-shaped slot.
7. A quantitative powder dispensing system as claimed in any preceding claim, wherein the motorised shutter is driven by a servomotor.
8. A quantitative powder dispensing system as claimed in any claim 1 to 6, wherein the motorised shutter is driven by a stepper motor.
9. A quantitative powder dispensing system as claimed in any preceding claim, wherein the vibration means comprises a vibromotor.
10. A quantitative powder dispensing system as claimed in claim 9, wherein the vibration means includes an offset weight.
ii. A quantitative powder dispensing system as claimed in any claim I to 8, wherein the vibration means comprises a pneumatic vibration device or an acoustic vibration device.
12. A method of quantitatively dispensing powder from a hopper comprising: providing vibration means for vibrating the powder; providing a motorised shutter between a dispensing outlet of the hopper and a receptacle for receiving dispensed powder; providing an electronic balance means for weighing the dispensed powder received by the hopper; providing a system control unit connected to the vibrating means, the motorised shutter, and the electronic balance means; opening and closing the dispensing outlet via the motorised shutter in response to a control loop feedback mechanism.
13, A method of quantitatively dispensing powder from a hopper as claimed in claim 12, wherein the control loop feedback mechanism is controlled via an iterative algorithm.
14. A method of quantitatively dispensing powder from a hopper as claimed in claim 13, wherein the iterative algorithm is a proportional integral derivative (P11)) algorithm.is. A method of quantitatively dispensing powder from a hopper as claimed in claim 13, wherein the iterative algorithm utilises fUzzy logic.16. A method of quantitatively dispensing powder from a hopper as claimed in any claim 13 to 15, wherein the iterative algorithm operates on five variable parameters: target weight of the dispensed powder; maximum flow rate of powder * 10 output through the dispensing outlet; tolerance of the target weight; error factor; and flow factor, 17. A method of quantitatively dispensing powder comprising the steps of; agitating the powder within a powder container; dispensing the powder through a shuttered aperture into an weighing receptacle associated with an electronic balance; wherein the aperture size is varied by operation of a shutter mechanism in response to feedback from the electronic balance.18. A quantitative powder dispensing system substantially as hereinbefore described with reference to and illustrated by the accompanying drawings.19. A method substantially as hereinbefore described with reference to and illustrated by the accompanying drawings.