Improvements in vibratory feeders

Abstract

A vibrating feeder having a feeder plate comprising a layered structure of a solid material and a material comprising voids, such as a metal foam, a sintered metal or glass, a ceramic, a foam polymer, an aerogel or an arrangement of spacers. Also particularly described is a mitre plate.

Description

TECHNICAL FIELD

[0001] The present invention relates to improvements in vibratory feeders, and in particular to improvements in feeder plates for use as part of such feeders. The invention also relates in particular to vibratory feeders using bevelled plates. BACKGROUND

[0002] It is a common requirement in the process industry to continuously feed a required amount of a powdered component, particularly when the manufacturing process is continuous in nature rather than batch processed. Vibratory feeders are a common way of performing this operation. Vibratory feeders are well known in the art and comprise a powder hopper which feeds powder onto a plate. The plate is typically vibrated by an electromagnet which is provided with an alternating voltage which acts on a magnetically sensitive element attached to the plate which is mounted on a flexible support. The vibrations induced in the plate cause the powder to move along the plate and fall off the edge, thereby depositing the powder in or on a process stream. The flow rate of the powder can be varied by varying the magnitude or frequency of the applied voltage.

[0003] In some set ups, the powder stream is added to a through stream of other components which are then mixed. An example of this process operation can be, for example, the addition of sugar to a through stream of granular foodstuff, such as breakfast cereal, which can then be shaken or otherwise mixed to evenly distribute the sugar.

[0004] However, in other set ups, the powder stream is deposited directly on a process stream in which the powder adheres to other components and no further mixing takes place. An example of this process operation can include the addition of a powdered material to a web of material which is then laminated. In the food industry, another example can be the addition of a flavouring to the surface of a flat foodstuff which is then packaged without further significant agitation of the product. In these processes, the lack of further mixing causes any unevenness in the spatial distribution of the powdered ingredient on the product stream to be reflected in the unevenness of that ingredient in the final product. This is particularly a problem in relation to unevenness in the distribution of powder across the width of the vibratory feeder plate.

[0005] In US 3,199,664 and US 3,123,203, vibratory feeders are provided in which an internal material (spheres or foam) transmits motion, i.e. the top and bottom layers move relative to each other, such that by imparting motion to the top layer relative to the bottom layer, the product moves along the top layer. However, allowing relative motion between the top and bottom layers allows an additional degree of freedom of motion which is undesirable for the uniform delivery of granules.

[0006] It is an object of the present invention to provide a vibratory feeder in which the required motion is transmitted without variation to the top surface on which granules are delivered, thereby enabling more uniform delivery of granules.

[0007] It is also an object of the present invention to provide a vibratory feeder having reduced variation in powder feed rate. SUMMARY

[0008] Accordingly, the present invention provides a vibratory feeder comprising a feeder plate comprising a laminate formed of two different layers: (a) a first solid layer; and (b) a second layer comprising voids.

[0009] Preferably, the feeder plate further comprises a third solid layer of material arranged on the side of the second layer opposite the first solid layer.

[0010] In either case, preferably the second layer comprises a metal foam.

[0011] Alternatively, preferably the second layer comprises a sintered metal.

[0012] Alternatively, preferably the second layer comprises a ceramic.

[0013] Alternatively, preferably the second layer comprises a porous matrix.

[0014] Alternatively, preferably the second layer comprises a spacer arrangement.

[0015] Alternatively, preferably the second layer comprises a foam polymer.

[0016] Alternatively, preferably the second layer comprises a glass, for example a sintered glass.

[0017] Alternatively, preferably the second layer comprises an aerogel.

[0018] In any aspect of the invention, preferably the stiffness of the feeder plate is greater than the stiffness of a feeder plate of the same mass formed of the solid material of the first layer.

[0019] In any aspect of the invention, preferably the stiffness of the feeder plate is in a plane perpendicular to the feed surface of the vibratory feeder.

[0020] Alternatively, preferably the stiffness of the feeder plate is in a plane parallel to the feed surface of the vibratory feeder.

[0021] Further alternatively, preferably the stiffness of the feeder plate is isotropic.

[0022] Further, in any aspect of the invention, preferably the feeder plate is a mitred plate.

[0023] BRIEF DESCRIPTION OF DRAWINGS

[0024] The application is described with reference to the accompanying drawings, in which:

[0025] Figure 1 is a perspective view of a known vibratory feeder plate;

[0026] Figure 2A and Figure 2B is an elevational view of a known vibratory feeder plate;

[0027] Figure 3 is a perspective view of a known vibratory feeder skid plate;

[0028] Figure 4A and Figure 4B is an elevational view of a known vibratory feeder skid plate;

[0029] Figure 5 is a plan view of a vibratory feeder skid plate depositing powder onto an item on a conveyor belt;

[0030] Figure 6 is a graph showing measured and predicted values of displacement of a point on a skid plate in the vertical (Y) direction and the side-to-side (Z) direction;

[0031] Figure 7 is a graph showing variation in powder deposition weight across a known skid plate;

[0032] Figure 8 is a simulation showing variation in total displacement across a known skid plate;

[0033] Figure 9 is a graph showing maximum total displacement on a skid plate formed of different stiffness materials;

[0034] Figures 10 to 12 shows various layer arrangements in a vibratory feeder plate of the application; and

[0035] Figure 13 is a plan view of a portion of a porous material forming part of a vibratory feeder plate of the application.

[0036] Figure 14 shows the profile of displacement, velocity and acceleration of a conventionally manufactured vibratory feeder plate, where stiffness is imparted by folds in the metal. The profile is taken at 0.067 seconds in a simulation driven at 48 Hz.

[0037] Figure 15 shows the profile of displacement, velocity and acceleration of a vibratory feeder plate of the application comprising a 50mm honeycomb layer (vertical honeycomb) between first and third solid material layers. The profile is taken at 0.067 seconds in a simulation driven at 48 Hz.

[0038] Figure 16 The profile of displacement, velocity and acceleration of a vibrating feeder plate of the invention is shown, comprising a 100 mm honeycomb layer between a first solid layer and a third solid material layer, wherein the honeycomb layer is rotated such that the tubes formed by the honeycomb are parallel to the first and second solid layers (rotated honeycomb). The profile is taken at 0.056 seconds in a simulation driven at 48 Hz.

[0039] Figure 17 The profile of displacement, velocity and acceleration of a vibrating feeder plate of the invention is shown, comprising a 50 mm vertical honeycomb layer between a first solid layer and a third solid material layer. The profile is taken at 0.056 seconds in a simulation driven at 48 Hz.

[0040] Figure 18 A preferred vertical honeycomb structure is shown. DETAILED DESCRIPTION

[0041] Figure 1 A part of a known vibrating feeder is shown in perspective view, generally designated by 1. The feeder 1 comprises a feeder plate 2, which is surrounded on three sides by walls 3. Powder is deposited on the feeder plate 2 as indicated by arrow 4. Vibration of the plate along its long axis causes the powder to flow towards the open edge of the feeder plate 2, as indicated by arrow 8, where the powder falls and is deposited on the process line.

[0042] Figure 2A and Figure 2B A vibrating feeder of the invention is shown in front view. Figure 1 The electromagnet 5 is arranged to impart a cyclic force to the feeder plate 2, which is mounted on a flexible mount 6, which causes the feeder plate to oscillate as indicated by the curved arrow 7. The walls 3 of the feeder 1 provide the feeder plate 2 with a degree of structural stiffness.

[0043] Figure 3 A part of a different known vibrating feeder is shown in perspective view, generally designated by 1. Similar elements already described with reference to Figure 1 are numbered accordingly and will not be described further. In this feeder, the feeder plate 2 is shaped such that the open edge 9 of the plate 2 is at an angle, i.e. not perpendicular to the direction of flow of the powder. A downwardly extending skirt 10 is also provided at the edge 9 of the feeder plate 2. The skirt 10 as well as the walls 3 of this feeder further provide the feeder plate 2 with a degree of structural stiffness. This configuration of the feeder plate 2 with an angled edge 9 is known in the industry as a “bevelled plate”.

[0044] Figure 4A andFigure 4B In Figure 2A and Figure 2B a manner related to Figure 1 a front view of a vibratory feeder. Similar elements that have been described in connection with the previous figures are numbered accordingly and will not be discussed further. Figure 3

[0045] One known advantage of the inclined apron form of vibratory feeder is that the inlet hopper from which powder is deposited onto the feeder plate 2 can be positioned to one side of the production line, such as a conveyor belt, allowing the whole feeder system to be positioned more conveniently and for the feed material to be removed from the production line more easily for cleaning, for example. In Figure 5 a plan view of this type of arrangement is shown. The figure shows a portion of a vibratory feeder 1 positioned above a conveyor belt 11 moving in the direction of arrow 12. Powder is deposited on the inclined apron 2 as shown by arrow 4. The powder flows down the inclined apron in the direction of arrow 8, falls over the edge 9 and falls onto the product 13 on the conveyor belt 11. As the product passes the edge 9 of the inclined apron 2, powder is deposited on the surface of the product 13 as shown.

[0046] In the example described above, the motion of the feeder plate 2 can be surmised by a simple circular oscillation as shown by arrow 7. This oscillatory motion has the effect of lifting particles and propelling them along the plate as shown by arrow 8. Random dispersal of particles perpendicular to arrow 8 would be expected to result in an even distribution of particles across the plate. If this were the only motion, then a uniform dose of particles across the width of the open edge of the plate would be expected. However, experimental observations suggest that this is not the case and there are significant differences in the flow rate of powder leaving the plate 2 at different positions along the edge.

[0047] To investigate this phenomenon, the inventors have investigated the motion of the plate. A high speed, high resolution camera system was used to monitor the displacement of the surface of the vibratory feeder plate at multiple locations and with various excitation zones by using digital image correlation (DIC). The inclined apron geometry was chosen and reflective dots were added to the surface of the inclined apron to aid imaging. The results of the imaging show that the motion of the inclined apron surface is much more complex than a simple oscillatory motion, but the flexing of the plate creates a complex pattern of vertical displacement across the plate surface.

[0048] A detailed mathematical model of the inclined apron was developed, combining plate eigenfrequency analysis and modal superposition and compared to experimental data from DIC analysis. The predictions of the model match the experimental data very well and show the resonance of the plate and the complex displacement pattern across the plate. Figure 6 ​Only one example of measured and predicted displacement along the Z axis (vertical displacement - hollow circle) and along the Y axis (left-right displacement perpendicular to the main body flow of powder - hollow triangle) is shown.

[0049] An experiment was then performed to measure the powder flow across the width of the scarf plate by collecting powder from each of a number of "channels" spanning the width of the edge 9 of the scarf plate. The width was divided into 18 such channels and powder was collected over a set time interval. Figure 7 The results of this experiment are shown in a graph. The solid line shows the mass of powder collected from each channel, and the dashed line shows the target required powder loading. It can be seen that there is considerable variation in powder delivery across the width of the device. If the target required powder loading is the minimum powder requirement, then all material delivered above this target would be characterised as waste.

[0050] Figure 8 Contour plots are shown which illustrate the distribution of total displacement across the scarf plate predicted by the model. It can be seen that there is a tendency for greater displacement at the larger channel numbers (towards the distal end of the plate), as shown by the experimental data.

[0051] The correspondence between the model predictions and the surface displacements measured by the DIC, and the correspondence between the model predictions and the powder flow experimental measurements, gives confidence that the model provides a good prediction of the performance of the vibratory feeder.

[0052] Based on this, the model was used to predict the maximum displacement of the surface of the scarf plate 2 as the stiffness of the scarf plate material was varied. Three different materials were considered: a low stiffness material (e.g. polymer), a medium stiffness material (e.g. aluminium) and a high stiffness material (e.g. steel). Figure 9 The results of the simulation for these three materials are shown in a graph. It can be seen that for the material with the lowest stiffness, the displacement 14 is greatest and the primary resonance frequency is higher. The material with the highest stiffness shows the smallest displacement 15 and the lowest primary resonance frequency. The material of intermediate stiffness shows a corresponding intermediate displacement 16.

[0053] This analysis shows that increasing the stiffness of the cleated plate reduces the maximum displacement of the cleated plate surface, resulting in the most uniform motion of the plate surface across the plate width. In other words, increasing the stiffness of the cleated plate minimizes the distortion of the cleated plate surface (in this case, distortion is defined as the distance an object is bent or twisted from its original position relative to other points on the surface of the cleated plate 2, not including rigid motion of the object imposed by external forces), resulting in the most uniform motion of the plate surface across the plate width. As a result, the initial consideration might lead a designer to simply select a material with inherently high stiffness (e.g., selecting steel over aluminum or polymer). However, in practice, materials with increased stiffness often have higher density. The result of this is that the cleated plate will have greater mass, and more power will be required to oscillate the plate.

[0054] However, the present inventors have found that, by using a composite material, an increase in the stiffness of the vibratory feeder's dosing plate can be achieved without a corresponding increase in mass.

[0055] Figure 10 A cross-sectional view of the present dosing plate is shown, generally designated by 2. The plate 2 includes a first, upwardly facing (in use) layer 17 of solid material that is attached to a second, downwardly facing layer 18 formed of a material having voids that reduce its bulk density. The top solid layer 17 provides a powder contact surface that can be easily cleaned and is less likely to harbor microbial contamination. This would be important if the vibratory feeder were to be used, for example, in a food processing environment. The second layer 18 provides stiffness through its microstructure, rather than through the inherent mass of the loose material from which it is formed. Exemplary materials include metal foams, sintered metals, and ceramics. If a closed cell metal foam is employed, it provides greater resistance to possible intrusion of contaminants. Overall, this construction provides a vibratory feeder plate 2 that is stiffer than a dosing plate of the same mass formed of the solid material of the first layer 17. The second layer 18 imparts stiffness to the laminate, which enables the top layer 17 and the second layer 18 to move together in the same direction to minimize distortion of the top layer surface.

[0056] Figure 11 An alternative dosing plate of the present invention is shown again in cross-sectional view, generally designated by 2. In this embodiment, the dosing plate includes a first, upwardly facing (in use) layer 17 of solid material that is attached to a second, downwardly facing layer 18 formed of a material having voids that reduce its bulk density. The top solid layer 17 provides a powder contact surface that can be easily cleaned and is less likely to harbor microbial contamination. This would be important if the vibratory feeder were to be used, for example, in a food processing environment. The second layer 18 provides stiffness through its microstructure, rather than through the inherent mass of the loose material from which it is formed. Exemplary materials include metal foams, sintered metals, and ceramics. If a closed cell metal foam is employed, it provides greater resistance to possible intrusion of contaminants. Overall, this construction provides a vibratory feeder plate 2 that is stiffer than a dosing plate of the same mass formed of the solid material of the first layer 17. The second layer 18 imparts stiffness to the laminate, which enables the top layer 17 and the second layer 18 to move together in the same direction to minimize distortion of the top layer surface. Figure 10two layers 17, 18 as described in embodiments of the invention, and an additional third layer 19 comprising solid material, optionally comprising the same material as the top layer 17. In this way, the exposed face of the feeder plate 2 is effectively sealed against contamination. The first solid layer and the third solid material layer do not have to be parallel, in some embodiments the third solid material layer is not parallel to the first solid layer. In preferred embodiments, the distance between the third solid material layer and the first solid material layer is narrower at the open edge of the feeder plate. The angle at which the distance between the third layer and the first layer narrows is chosen to minimize mass where rigidity is not required.

[0057] In embodiments where a third solid material layer 19 is present, the second layer 18 imparts rigidity to the stack, which enables the top layer 17 and the second layer 18 to move together in the same direction, and minimizes distortion of the top layer surface.

[0058] Figure 12 A third embodiment of a feeder plate of the invention is shown, also generally indicated by 2. In this embodiment, solid layers 17, 19 are provided at the top and bottom of the feeder plate, and these sandwich an inner layer 20 of porous material, i.e. material having regularly shaped gas-filled holes therein. Figure 13 The porous material is shown in plan view (not to scale) with voids 21 in the form of hexagonal prisms separated by walls 22 of solid material. This structure is similar to that of a honeycomb, and is preferably arranged so that the voids extend vertically from the upper layer 17 to the lower layer 19.

[0059] Figure 14 The profiles of displacement, velocity and acceleration of a conventionally manufactured vibratory feeder plate (skewer) are shown, in which the rigidity is imparted by folds in the metal. The profiles are taken at 0.067 seconds in a simulation driven at 48 Hz.

[0060] Figure 15 The profiles of displacement, velocity and acceleration of a vibratory feeder plate (skewer) of the invention comprising a 50mm honeycomb layer (vertical honeycomb) between the first and third solid material layers are shown. The profiles are taken at 0.067 seconds in a simulation driven at 48 Hz. By comparison Figure 14 and Figure 15 it can be seen that the skewer of the invention with a honeycomb second layer has a more uniform vibration pattern than Figure 14 the conventional skewer.

[0061] Figure 16The displacement, velocity, and acceleration profiles of a vibratory feeder plate of the present application are shown, including a 100 mm honeycomb layer between first and third solid material layers, where the internal honeycomb structure is rotated 90°, so that the tubes formed by the honeycomb are identical to the many features of the vertical and rotated honeycombs, but the displacement pattern in the rotated honeycomb is more non-uniform than the displacement pattern in the vertical honeycomb for several periods of time throughout the cycle. For comparison, Figure 17 A vertically oriented honeycomb is shown at the same time marker (0.056 seconds), which shows a more uniform profile. This leads to the conclusion that the vertical honeycomb is preferred, as Figure 18 shown. It can be said that the stiffness of the feeder plate is preferred in a plane perpendicular to the conveying surface of the vibratory feeder. However, in some embodiments, the stiffness of the feeder plate can be in a plane parallel to the conveying surface of the vibratory feeder. In other embodiments, the stiffness of the feeder plate is isotropic.

Claims

1. A vibratory feeder comprising a feeder plate, the feeder plate comprising a laminate of two different layers: (a) a first solid layer facing upward; and (b) a second layer facing downward comprising voids; wherein the second layer imparting stiffness to the laminate, which enables the first and second layers to move together in the same direction to minimize distortion of the first layer.

2. The vibratory feeder of claim 1, wherein, the feeder plate further comprising a third solid layer of material arranged on an opposite side of the second layer from the first solid layer.

3. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a metal foam.

4. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a sintered metal.

5. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a ceramic.

6. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a porous matrix.

7. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a spacer arrangement.

8. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a foam polymer.

9. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises a glass.

10. A vibratory feeder according to claim 1 or 2, wherein, the second layer comprises an aerogel.

11. A vibratory feeder according to claim 1 or 2, wherein, the stiffness of the feeder plate is greater than the stiffness of a feeder plate of the same mass formed from the solid material of the first layer.

12. A vibratory feeder according to claim 1 or 2, wherein, the stiffness of the feeder plate is in a plane perpendicular to a conveying surface of the vibratory feeder.

13. A vibratory feeder according to claim 1 or 2, wherein, the stiffness of the feeder plate is in a plane parallel to a conveying surface of the vibratory feeder.

14. A vibratory feeder according to claim 1 or 2, wherein, the stiffness of the feeder plate is isotropic.

15. A vibratory feeder according to claim 1 or 2, wherein, the feeder plate is a beveled plate.

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