Computer combination weighing apparatus

Abstract

A flexible collective discharge chute, arranged to receive articles from weigh hoppers of a combination weigher / CCW and flex upon receipt of those articles. The chute has a substrate 44 having a first surface 46 which receives the product, and a second opposed surface 48 arranged to face an air space 52 such that the substrate flexes into the air space in response to articles P being received by the first surface. The flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa·m3. The thickness of the substrate is preferably less than 5mm. The discharge chute is positioned below the weigh hoppers. The substrate of the chute is preferably plastic e.g. polyvinyl chloride, and is transparent. The chute may have a rigid chute portion 50 which may be made of metal e.g. steel. The articles maybe food products e.g. crisps, nuts, seeds, popcorn, dried fruits, bread products and confectionery.

Description

FIELD OF THE INVENTION The invention relates to a computer combination weighing apparatus. The invention also relates to a method of operating a computer combination weighing apparatus. BACKGROUND In the formation of packages of food product, such as bags of potato crisps or chips or trays of meat or poultry, many production lines involve the use of a feeder system that receives a supply of food product in bulk and feeds this product to a plurality of measuring units that measure out partial batches of that food product. Such systems are often referred to as dispersion feeder systems and may be incorporated as part of a system that combines the partial batches of product into complete batches meeting pre-set criteria. An example of a system that may form batches in this way would be a multihead weigher or computer combination weigher (CCW). A CCW is typically employed to form batches of food product having predetermined criteria as to weight by identifying a suitable combination of two or more partial batches measured by the weighing hoppers and dispensing these partial batches so that they can be packaged together. For example, a CCW may be set to form batches of potato crisps having a weight of 30 grams, and will look for weight combinations from the weighing hoppers that add up to approximately 30 grams. Batches of food product are dispensed by the weighing hoppers into a discharge chute which is positioned below the weighing hoppers. The discharge chute is typically made of metal and is arranged to guide the received food product to a common discharge point at the centre axis of the CCW. However, in conventional discharge chutes it has been found that food product often bounces upon contact with the surface of the discharge chute, thereby scattering the food product across the discharge chute. This increases the amount of time that it takes for an entire batch of food product to reach the common discharge point after being dispensed from the weighing hoppers. The scattering can also lead to breakage or damage of the food product. Furthermore, when the CCW is running at a high cycle speed, the scattering of food product may result in sequential batches of food product overlapping and interacting within the discharge chute. This means that a batch collected at the common discharge point may also include food product from a previous or subsequent batch, resulting in the collected batch weight differing from the target batch weight. The scattering of food product within discharge chutes has been found to be particularly prevalent for small batches of particular types of food product, such as confectionery, dried fruits, and nuts. An object of the present invention is to address one or more of these issues. SUMMARY OF INVENTION According to a first aspect of the invention, there is provided a computer combination weighing apparatus, comprising: a plurality of weighing hoppers; and a collective discharge chute positioned below the plurality of weighing hoppers, wherein the collective discharge chute comprises a flexible substrate having a first surface and an opposed second surface, wherein the first surface of the substrate is arranged to receive articles dispensed from the plurality of weighing hoppers, wherein the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3, and wherein the second surface of the substrate is arranged to face an air space such that the substrate is configured to flex into the air space in response to articles being received by the first surface of the substrate. In this way, articles dispensed from the weighing hoppers will be cushioned upon receipt by the flexible substrate such that the scattering of articles within the collective discharge chute is significantly reduced. In particular, as the substrate is able to flex into an air space, the kinetic energy of the dispensed articles is absorbed thereby providing an effective bounce reduction mechanism. This contrasts with, for example, collective discharge chutes having a rigid surface (e.g. metal) for receiving articles, which are prone to causing significant scattering of articles. By reducing the scattering of articles, this results in reduced article damage and breakage, increased production speed, and batches of articles collected at the common discharge point having a weight which more accurately corresponds to a batch target weight. Moreover, the simple construction by which a flexible substrate is allowed to flex into an air gap makes the cost of the discharge chute low compared to rigid chute provided with cushioning means, and allows existing systems to be conveniently retro-fitted with the new discharge chute. In some cases, the first surface of the substrate may receive articles falling under gravity directly from the weighing hoppers. In other cases, one or more pool hoppers may be arranged downstream of each weighing hopper and configured to temporarily store articles received from the weighing hopper while a decision is being made on a selection of the articles to be dispensed. Preferably, the substrate is arranged such that the first surface of the substrate directly receives articles falling under gravity from one or more of the weighing hoppers and / or from one or more pool hoppers arranged downstream of respective ones of the weighing hoppers. The collective discharge chute may thus be solely responsible for receiving the dispensed articles and directing them to a common discharge point. Preferably each hopper configured to dispense articles that are directly received by the first surface of the substrate comprises a hopper with a doubleopening door. Double-opening door hoppers, i.e. those having two doors that move substantially simultaneously to dispense product, dispense product quickly and typically substantially vertically, but are most prone to inducing scattering of product. Nonetheless, the present arrangement may also be used with singleopening door hoppers. The substrate may be also referred to as a sheet. Preferably, the substrate comprises or consists of plastic. In this way, the build cost of the collective discharge chute may be significantly reduced compared to, for example, using a collective discharge chute which comprises or consists of a metal such as steel. Preferably, the plastic is polyvinyl chloride, polyurethane, polypropylene or polyethylene. Preferably, the substrate is transparent. More specifically, the substrate is transparent such that at least a section of the collective discharge chute is also transparent. In this way, it is possible for machine operators to observe the articles being received and directed by the collective discharge chute. This can assist with the diagnosis of any issues with the computer combination weighing apparatus, e.g. blockages can be observed. As indicated above, the flexural rigidity of the substrate at an environmental temperature and pressure of 20°C and 101.325 kPa is less than 10 Pa m3 Flexural rigidity can be measured experimentally by measuring the force required to bend the substrate by one unit of curvature. Alternatively, as the surface of the chute approximates a plate, the flexural rigidity may be determined using the equation: 12(1-v2) where D is the flexural rigidity, E is the Young's Modulus of the material forming the substrate, t is the thickness of the substrate, and v is the Poisson’s ratio of the material forming the substrate. Preferably, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa m2, preferably less than 2 Pa m3, more preferably less than 1 Pa m3 most preferably less than 0.5 Pa m3 A lower flexural rigidity improves the cushioning action of the chute and further reduces scattering. Preferably, the flexural rigidity of the substrate at20°C and 101.325 kPa is greater than 0.0001 Pa m3, preferably greater than 0.001 Pa m3, more preferably greater than 0.005 Pa m3, most preferably greater than 0.01 Pa m3. A flexural rigidity above these lower limits provides a good balance between durability and scattering reduction. Preferably, the thickness of the substrate is at most 5 mm, preferably at most4 mm, more preferably at most 3mm, most preferably at most 2mm. Providing a substrate of a low thickness is a convenient way to contribute to achieving a low flexural rigidity. Preferably, the thickness of the substrate is at least 0.1 mm, preferably at least 0.2 mm, more preferably at least 0.5mm, most preferably at least 1 mm. Again, ensuring that the thickness of the substrate is above these lower limits helps ensure good durability. Preferably, the Young’s modulus of the substrate at20°C and 101.325 kPa is less than 15 GPa, preferably less than 10 GPa, more preferably less than 5 GPa, most preferably less than 3GPa. These materials can conveniently be formed into chutes with the required flexural rigidity at preferred thicknesses. Preferably, the Young’s modulus of the substrate at 20°C and 101.325 kPa is greater than 0.01 GPa, preferably greater than 0.05 GPa, more preferably greater than 0.1 GPa, most preferably greater than 1GPa. Again, these lower limits provides a good balance between durability and scattering reduction. Preferably, the flexural modulus of the substrate at 20°C and 101.325 kPa is less than 15 GPa, preferably less than 10 GPa, more preferably less than 5 GPa, most preferably less than 3GPa. Preferably, the flexural modulus of the substrate at 20°C and 101.325 kPa is greater than 0.01 GPa, preferably greater than 0.05 GPa, more preferably greater than 0.1 GPa, most preferably greater than 1GPa. In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3 and greater than 0.0001 Pa m3 In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa-m3 and greater than 0.001 Pa m3 In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 2 Pa m3 and greater than 0.005 Pa m3. In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3, and the thickness of the substrate is at least 0.2 mm and / or at most 4 mm. In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa m3, and the thickness of the substrate is at least 0.5 mm and / or at most 3 mm. In another example, the flexural rigidity of the substrate at20°C and 101.325 kPa is less than 2 Pa m3, and the thickness of the substrate is at least 0.5 mm and / or at most 3 mm. In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3, and the Young’s modulus of the substrate is less than 15 GPa and / or greater than 0.01 GPA. In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3, and the Young’s modulus of the substrate is less than 10 GPa and / or greater than 0.05 GPa. In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa m3, and the Young’s modulus of the substrate is less than 5 GPa and / or greater than 0.1 GPa. In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3, the thickness of the substrate is at most 4 mm and / or the Young’s modulus of the substrate is less than 10 GPa. In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa m3 the thickness of the substrate is at most 3 mm and / or the Young’s modulus of the substrate is less than 5 GPa. In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 2 Pa m3, the thickness of the substrate is at most than 2 mm and / or the Young’s modulus of the substrate is less than 5 GPa In one example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3 and / or greater than 0.0001 Pa m3, the thickness of the substrate is at most 3 mm, and the Young’s modulus of the substrate is less than 10 GPa. In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa m3 and / or greater than 0.001 GPa, the thickness of the substrate is at most 2 mm, and the Young’s modulus of the substrate is less than 5 GPa. In another example, the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 2 Pa-m3 and / or greater than 0.005 Pam3, the thickness of the substrate is at most 2 mm, and the Young’s modulus of the substrate is less than 5 GPa. It will be appreciated that for isotropic materials the Young’s modulus is equivalent to the flexural modulus. Advantageously, the above parameters result in particularly effective cushioning of articles received by the substrate. Preferably, wherein the substrate comprises a first layer and a second layer, the first layer comprising a first material and the second layer comprising a different second material. For example, the first material may be a polyvinyl chloride sheet, and the second layer may be a coating applied to a surface of the sheet. In further examples, the substrate may comprise more than two layers. Preferably, the collective discharge chute further comprises a rigid chute portion, wherein the rigid chute portion has a flexural rigidity that is greater than the flexural rigidity of the substrate, and optionally wherein the substrate is coupled to the rigid chute portion. Preferably the rigid chute portion has a flexural rigidity that is at least double the flexural rigidity of the substrate, preferably at least ten times the flexural rigidity of the substrate, most preferably at least 100 times the flexural rigidity of the substrate. Preferably, the air space is defined between the substrate and the rigid chute portion. In this way, the enclosed or partially enclosed air space acts as an air cushion which further improves the cushioning effect provided by the flexible substrate. Preferably, the average air space between the substrate and the rigid chute portion is at least 5 mm, preferably at least 10 mm, most preferably at least 20 mm. Preferably, the substrate is arranged to be substantially coextensive with the rigid chute portion. In other words, the substrate is arranged to extend over substantially the entire area of an inner surface of the rigid chute portion. In this way, the extent of the substrate means that the scattering reduction of articles is optimised. Advantageously, such a system may be switched between different applications by selectively installing or removing the flexible chute portion. It is also possible to achieve this arrangement by retrofitting existing computer combination weighing apparatuses. Alternatively, the substrate may be arranged to be substantially coextensive with an upper area only of the rigid chute portion and / or may extend above the rigid chute portion. Preferably, the substrate and the rigid chute portion are arranged such that an upper section of the collective discharge chute and a lower section of the collective discharge chute are provided by the substrate and the rigid chute portion respectively. In this way, the substrate is located to directly receive articles dispensed from the weighing hoopers where maximum cushioning is particularly advantageous. Further cushioning is less important at the lower section of the collective discharge chute, so a rigid chute portion is used to ensure that the articles are reliably guided to the common discharge point. Preferably, the rigid chute portion comprises or consists of metal. For example, the metal may be steel. Preferably, the flexural rigidity of the rigid chute portion at 20°C and 101.325 kPa is more than 10 Pa m3, preferably more than 20 Pa m3, more preferably more than 100 Pa m3, most preferably more than 500 Pa m3. Preferably, the first surface of the substrate defines a substantially parabolic surface. Such a surface is particularly suited to introducing lateral movement into the vertically falling product in order to bring the product to a common discharge point. Furthermore, the sorts of flexible materials used to form the substrate may conveniently be formed into parabolic shapes for any particular system. According to a second aspect of the invention, there is provided a method of operating a computer combination weighing apparatus, the apparatus comprising a plurality of weighing hoppers and a collective discharge chute positioned below the plurality of weighing hoppers, the collective discharge chute comprising a flexible substrate having a first surface and an opposed second surface, the first surface of the substrate being arranged to receive articles dispensed from the plurality of weighing hoppers, and the flexural rigidity of the substrate at 20°C and 101.325 kPa being less than 10 Pa m3, wherein the method comprises: dispensing articles from the plurality of weighing hoppers; receiving the articles by the first surface of the substrate, wherein the second surface of the substrate is arranged to face an air space such that the substrate flexes into the air space in response to articles being received by the first surface of the substrate. Preferably, dispensing the articles from the plurality of weighing hoppers comprises: dispensing the articles from the plurality of weighing hoppers in batches of less than 200g, preferably less than 100g, more preferably less than 50g, most preferably less than 30g. Small batches of product are particularly prone to scattering, as there is less opportunity for collision between the articles to disperse kinetic energy. In this way, the flexible substrate is used to cushion small batches of articles which are particularly prone to scattering. Preferably, the articles comprise one or more of: crisps (also referred to as chips, particularly potato or com chips); popcorn; nuts; seeds; dried fruits; confectionery; and breaded products. In this way, the flexible substrate is used to cushion types of articles which are particularly prone to scattering. Preferably, each article weighs less than 10g, preferably less than 5g, more preferably less than 2g, most preferably less than 1g. In this way, the flexible substrate is used cushion light articles which are particularly prone to scattering. Preferably, each article has a maximum dimension of less than 5cm, preferably less than 3cm, more preferably less than 2cm, most preferably less than 1 cm. In this way, the flexible substrate is used cushion small articles which are particularly prone to scattering. Preferably, the articles comprise a particulate coating, such as a coating of breadcrumbs or sugar. Such articles have an increased chance of disintegrating when received by a collective discharge chute, so it is particularly advantageous to cushion these articles using a flexible substrate. The second aspect may include one or more of the preferable features of the first aspect. According to a third aspect of the invention, there is provided a computer combination weighing apparatus, comprising: a plurality of weighing hoppers; and a collective discharge chute positioned below the plurality of weighing hoppers, wherein the collective discharge chute comprises a flexible substrate having a first surface and an opposed second surface, wherein the first surface of the substrate is arranged to receive articles dispensed from the plurality of weighing hoppers, wherein the Young’s modulus of the substrate at 20°C and 101.325 kPa is less than 15 GPa, wherein the thickness of the substrate is at most 5 mm, and wherein the second surface of the substrate is arranged to face an air space such that the substrate is configured to flex into the air space in response to articles being received by the first surface of the substrate. The third aspect may include one or more of the preferable features of the first aspect. In particular, preferably, the Young’s modulus of the substrate at 20°C and 101.325 kPa is less than 10 GPa, more preferably less than 5 GPa, most preferably less than 3GPa. Preferably, the Young’s modulus of the substrate at 20°C and 101.325 kPa is greater than 0.01 GPa, preferably greater than 0.05 GPa, more preferably greater than 0.1 GPa, most preferably greater than 1GPa. Preferably, the thickness of the substrate is at most 5 mm, preferably at most 4 mm, more preferably at most 3 mm, most preferably at most 2 mm. Preferably, the thickness of the substrate is at least 0.1 mm, preferably at least 0.2 mm, more preferably at least 0.5 mm, most preferably at least 1 mm. In one example, the thickness of the substrate is at most 4 mm, and the Young’s modulus of the substrate is less than 10 GPa. In another example, the thickness of the substrate is at most 3 mm, and the Young’s modulus of the substrate is less than 5 GPa. In another example, the thickness of the substrate is at most 2 mm, and the Young’s modulus of the substrate is less than 5 GPa. In one example, the thickness of the substrate is at most 4 mm, and the Young’s modulus of the substrate is less than 10 GPa and / or greater than 0.01 GPa. In another example, the thickness of the substrate is at most 3 mm, and the Young’s modulus of the substrate is less than 5 GPa and / or greater than 0.05 GPa. In another example, the thickness of the substrate is at most 2 mm, and the Young’s modulus of the substrate is less than 5 GPa and / or greater than 0.1 GPa. In one example, the thickness of the substrate is at most 4 mm and at least 0.2 mm, and optionally the Young’s modulus of the substrate is less than 10 GPa. In another example, the thickness of the substrate is at most 3 mm and at least 0.5 mm, and optionally the Young’s modulus of the substrate is less than 5 GPa. In another example, the thickness of the substrate is at most 2 mm and at least 1 mm, and optionally the Young’s modulus of the substrate is less than 3 GPa. In one example, the Young’s modulus of the substrate is less than 15 GPa and greater than 0.01 GPa, and optionally the thickness of the substrate is at most 5 mm. In another example, the Young’s modulus of the substrate is less than 10 GPa and greater than 0.05 GPa, and optionally the thickness of the substrate is at most 4 mm. In another example, the Young’s modulus of the substrate is less than 5 GPa and greater than 0.1 GPA, and optionally the thickness of the substrate at most than 3 mm. According to a fourth aspect of the invention, there is provided a method of operating a computer combination weighing apparatus, the apparatus comprising a plurality of weighing hoppers and a collective discharge chute positioned below the plurality of weighing hoppers, the collective discharge chute comprising a flexible substrate having a first surface and an opposed second surface, the first surface of the substrate being arranged to receive articles dispensed from the plurality of weighing hoppers, wherein the Young’s modulus of the substrate at 20°C and 101.325 kPa is less than 15 GPa, wherein the thickness of the substrate is at most 5 mm, wherein the method comprises: dispensing articles from the plurality of weighing hoppers; receiving the articles by the first surface of the substrate, wherein the second surface of the substrate is arranged to face an air space such that the substrate flexes into the air space in response to articles being received by the first surface of the substrate. This corresponds to a method of operating a computer combination weighing apparatus according to the third aspect of the invention. All of the preferred features of the second aspect may be provided in this context. According to a fifth aspect of the invention, there is provided a computer combination weighing apparatus, comprising: a plurality of weighing hoppers; and a collective discharge chute positioned below the plurality of weighing hoppers, wherein the collective discharge chute comprises a flexible substrate having a first surface and an opposed second surface, wherein the first surface of the substrate is arranged to receive articles dispensed from the plurality of weighing hoppers, and wherein the second surface of the substrate is arranged to face an air space such that the substrate is configured to flex into the air space in response to articles being received by the first surface of the substrate, wherein the Young’s modulus and thickness of the flexible substrate are selected such that the flexible substrate may be elastically deformed between a curved state while the substrate is arranged to receive articles dispensed from the plurality of weighing hoppers and a substantially flat state when the substrate is removed for cleaning. These embodiments take advantage of the fact that chutes formed of flexible substrates may be removed from the combination weigher and deform elastically into a flat state for cleaning. This makes maintenance significantly easier. It will be appreciated that the preferred features described in accordance with the preceding first and third aspects also apply in this context. According to a sixth aspect of the invention, there is provided a method of operating a computer combination weighing apparatus, the apparatus comprising a plurality of weighing hoppers and a collective discharge chute positioned below the plurality of weighing hoppers, the collective discharge chute comprising a flexible substrate having a first surface and an opposed second surface, the first surface of the substrate being arranged to receive articles dispensed from the plurality of weighing hoppers, wherein the Young’s modulus and thickness of the flexible substrate are selected such that the flexible substrate may be elastically deformed between a curved state while the substrate is arranged to receive articles dispensed from the plurality of weighing hoppers and a substantially flat state when the substrate is removed for cleaning, wherein the method comprises: dispensing articles from the plurality of weighing hoppers; receiving the articles by the first surface of the substrate, wherein the second surface of the substrate is arranged to face an air space such that the substrate flexes into the air space in response to articles being received by the first surface of the substrate. BRIEF DESCRIPTION OF DRAWINGS The present invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a perspective view of a computer combination weighing apparatus; Figure 2 is a schematic view of the computer combination weighing apparatus of Figure 1; Figure 3 is a schematic cross-sectional view of a collective discharge chute according to another embodiment of the invention; and Figure 4 is a schematic cross-sectional view of a collective discharge chute according to another embodiment of the invention. DETAILED DESCRIPTION Figure 1 shows a computer combination weighing apparatus 100. The combination weighing apparatus 100 includes a dispersion table 10, a plurality of feeder troughs 11, a plurality of pool hoppers 20, a plurality of weighing hoppers 30, and a collective discharge chute 40. As shown in Figure 2, food product P is received onto the dispersion table 10, which acts as the supply position for the food product. It will be appreciated that articles other than food product P may also be received by the dispersion table 10. The dispersion table 10 is configured to rotate about a vertical central axis C to move the food product P to the edge of the dispersion table 10 and to distribute food product P to the plurality of feeders 11. Each feeder trough 11 comprises a respective vibratory motor 12 coupled to the trough. In use, the vibratory motor 12 is made to vibrate with certain parameters, e.g. amplitude, frequency and time, in order to transport product P along the feeder trough 11 and into a pool hopper 20. In general, more product P will be transported along the feeder trough 11 with a larger vibration amplitude and a longer vibration time. Each vibratory motor 12 of the vibratory feeder is coupled to a controller 50 (also referred to as a control unit), which is able to control when the feeder transports food product P to the pool hopper 20 and the operation parameters of the motor 12 used to transport the food product P. Each pool hopper 20 is configured to temporarily hold the food product P supplied by the feeder 11. Each pool hopper 20 has a gate 21 at its lower end and opening said gate allows the product P to be dispensed into the corresponding weighing hopper 30 located therebeneath. Each pool hopper 20 is connected to the controller 50, which controls when the pool hopper 20 dispenses food product P into the weighing hopper 30. Each weighing hopper 30 is configured to temporarily hold food product P received via the pool hopper 20 from the feeder 11. Each weighing hopper 30 has a gate 31 at its lower end for dispensing product P. Any product P dispensed from a weighing hopper 30 is received in the discharge chute 40, which brings all product P to a common discharge point 42 typically at the centre axis of the system. Each weighing hopper 30 is coupled to a load cell 32, which weighs the hopper and so is able to determine the weight of the contents of the hopper. The load cell 32 is coupled to the controller 50 so that the controller can obtain the weight value of the product P in the weighing hopper 30. The gate 31 of each weighing hopper 30 is also connected to the controller 50 so that the opening and closing of the gate 31 can be controlled by the hopper 50. In practice, the controller 50 will identify a number of weighing hoppers 30 that contain product P whose total weight best corresponds to predetermined criteria for a batch of food product. The controller 50 will then open the gates of the corresponding weighing hoppers 30 to bring the partial batches of food product P together. The controller 50 will then cause the pool hoppers 20 corresponding to the weighing hoppers 30 that were just emptied to dispense their product into the corresponding weighing hoppers 30, which will then weigh the new partial batch of product R The controller 50 will also cause the feeders 11 to feed new product into the pool hoppers 20 that were just emptied. The controller 50 will then repeat the process with the set of partial batches in the weighing hoppers 30. The collective discharge chute 40 comprises a substrate 44 having a first surface 46 and an opposed second surface 48. The first surface 46 is arranged to directly receive product P dispensed from the weighing hoppers 30. That is, following opening of the gate 31, the first surface 46 will be the next surface that the dispensed product P contacts. The substrate 44 may also be referred to as a sheet. The substrate 44 is arranged to slope towards the common discharge point 42 such that the product P is conveyed towards the discharge point 42 under the force of gravity. In one example, the substrate 44 may be shaped to define a paraboloid, e.g. the first surface 46 forms a truncated conical surface. The second surface 48 of the substrate 44 is arranged to face towards an air space 52. In particular, in the embodiment illustrated in Figure 2, the air space 52 is arranged immediately adjacent the second surface 48, i.e. the second surface 48 interfaces with the air space 52. The substrate 44 is configured to have a flexural rigidity (at 20°C and 101.325 kPa) of less than 0.5 Pa m3 This configuration of the substrate 44 means that the substrate 44 is able to substantially flex into the air space 52 in response to product P being received by the first surface 46. Advantageously, this provides a cushioning effect which prevents the scattering of product P across the collective discharge chute 40. By reducing the scattering of product P, product P is less likely to become damaged within the collective discharge chute 40, the time taken for an entire batch of product P to reach the common discharge point 42 after being dispensed is reduced, and the likelihood of consecutive batches of product P becoming mixed up in the collective discharge chute 40 is also reduced. In contrast, for example, conventional collective discharge chutes are typically made from metal sheets which are rigid and / or are not able to substantially flex when product is dispensed onto the collective discharge chute, thereby resulting in significant bouncing and scattering of product. It will be understood that the flexural rigidity of the substrate 44 is dependent on the thickness and material type of the substrate 40. In particular, the flexural rigidity, D, may be determined based on the following equation: Ei3 where E is the Young’s modulus of the substrate, t is the thickness of the substrate, and v is the Poisson’s ratio of the substrate. The flexural rigidity may also be referred to as bending stiffness. Of course, it will also be appreciated that the flexural rigidity can also be determined experimentally using bending testing methods that are standard in the art, e.g. involving the application of a fixed load or deflection to a sample of substrate and measuring the resulting deflection or load respectively. An appropriate flexural rigidity for providing a significant cushioning effect may be achieved by selecting the substrate 40 to have a thickness approximately 1 to 2 mm, and a Young’s modulus of less than 3 GPa. Examples of particularly suitable material types for forming the substrate 44 with these properties include polyvinyl chloride, polyurethane, polypropylene or polyethylene. Another advantage of using a substrate of this sort is that it may be removed from the combination weigher and deformed elastically into a substantially flat state for cleaning. In particular, a 1 to 2 mm film formed of polyvinyl chloride, polyurethane, polypropylene or polyethylene can be removed from the supports holding it in position below the weighing hoppers and flexed into a flat state without plastically deforming the film. In one example, the substrate 44 may be transparent. Advantageously, this means that product P within the collective discharge chute 40 can be observed through the substrate 44 which can assist with the diagnosis of issues with the computer combination weighing apparatus 100, e.g. blockages can be observed. It is also possible for the substrate 44 to comprise a plurality of layers, such as a first layer comprising a first material and a second layer comprising a different second material. In one example, the first material may be a polyvinyl chloride sheet, and the second layer may be a coating applied to a surface of the sheet. The collective discharge chute 40 described with reference to Figure 2 corresponds to a basic embodiment of the collective discharge chute 40. Various other embodiments of the collective discharge chute 40 are also possible, for example as will now be described with reference to Figure 3 and 4. Figure 3 is a schematic cross-sectional view of a collective discharge chute 40 according to another embodiment of the invention. In this embodiment, the collective discharge chute 40 comprises a rigid chute portion 50. The rigid chute portion 50 has a flexural rigidity that is greater than the flexural rigidity of the substrate 44, e.g. the flexural rigidity of the rigid chute portion 50 (at 20°C and 101.325 kPa) may be more than 1000 Pa m3 In one example, the rigid chute portion 50 may be made of stainless steel of 5mm thickness. It will be appreciated that the substrate 44 in this embodiment has the same properties and general configuration as discussed above with reference to Figures 1 to 2. The rigid chute portion 50 is configured to support the substrate 44. For example, as illustrated in Figure 3, the substrate 44 is coupled to the rigid chute portion 50 by upper and lower supports 54, which may be small spacing elements arranged at regular intervals around the periphery of the rigid chute portion 50, preferably along the upper and lower edges of the rigid chute portion 50 and adhered to the facing surfaces of the rigid chute portion 50 and the substrate 44. While this arrangement is shown here for illustrative purposes, it will be appreciated that the specific support mechanism and coupling between the substrate 44 and rigid chute portion 50 may vary, e.g. only one continuous support 54 may be used along the upper and / or lower edge of the rigid chute portion 50. The substrate 44 and rigid chute portion 50 are arranged such that the air space 52 is defined or located between the substrate 44 and rigid chute portion 50. The air space 52 may thus be referred to as an air gap between the substrate 44 and rigid chute portion 50, i.e. the air space 52 is enclosed or partially enclosed by the substrate 44 and the rigid chute portion 50. When product P is received by the substrate 44, the substrate 44 flexes into the air gap which acts as an air cushion such that the scattering of product P is further reduced. It will be appreciated, however, that in some embodiments additional layers or sheets of material may be present in the air gap 52 between the substrate 44 and rigid chute portion 50, e.g. the rigid chute portion 50 may have a coating layer. In the illustrated embodiment, the substrate 44 is arranged to coextend with the rigid chute portion 50. That is, the substrate 44 extends substantially across the same area as the rigid chute portion 50. In other embodiments this arrangement may differ, e.g. the substrate 44 may only extend across an upper area of the rigid chute portion 50. The substrate 44 and the rigid chute portion 50 are formed in substantially the same shape, e.g. the substrate 44 and the rigid chute portion may both define paraboloids which are offset from one another. The substrate 44 and the rigid chute portion 50 may therefore be described as being substantially parallel. It will be appreciated, however, that the substrate 40 and the rigid chute portion 50 may not necessarily be arranged parallel to one another, and the distance between the substrate 40 and the rigid chute portion 50 (i.e. the width of the air gap) may vary. For example, if only the upper support 54 is used to secure the substrate 44 to the rigid chute portion 50, the substrate 44 may be arranged to directly contact (i.e. rest against) the rigid chute portion 50 at a lower section of the rigid chute portion 50. Figure 4 is a schematic cross-sectional view of a collective discharge chute 40 according to another embodiment of the invention. In this embodiment, the collective discharge chute 40 may be described as having an upper section 54 and a lower section 56. The upper section 54 is provided by the flexible substrate 44 and the lower section 56 is provided by the rigid chute portion 50. The flexible substrate 44 may be supported by its upper edge by a ring-shaped frame that surrounds the CCW, and which itself is supported by a number of arms extending from vertical support poles. In other words, the substrate 44 (or upper section 54) is arranged to receive product P directly from the weighing hoppers, and the rigid chute portion 50 (or lower section 56) is arranged to receive product P from the substrate 44 and guide the product to the common discharge point 42. The flexible upper section 54 provides maximum cushioning, whereas the rigid lower section 56 provides reliable guiding of product P to the common discharge point 42. In the illustrated embodiment, the substrate 44 and the rigid chute portion 50 partially overlap. In other embodiments, the rigid chute portion 50 may be arranged to extend adjacent the second surface 48 of the substrate 44 over substantially the entire upper section 54, such as described above with reference to Figure 3. The rigid chute portion 50 may be used to support the substrate 44, or the substrate 44 may be supported by other elements of the apparatus 100. Again, it will be appreciated that the substrate 44 and rigid chute portion 50 in this embodiment have the same properties and general configuration as discussed above with reference to Figures 1 to 3. Use of the collective discharge chute 40 described above is particularly advantageous for types of food product P which are prone to bouncing and scattering, such as crisps; popcorn; nuts; seeds; dried fruits; confectionery; and breaded products. More generally, it has been found that the collective discharge chute 40 is particularly advantageous for articles weighing less than 10g, preferably less than 5g, more preferably less than 2g, most preferably less than 1g. It has also been found that the collective discharge chute 40 is particularly advantageous for articles dispensed from weighing hoppers in batches of less than 200g, preferably less than 100g, more preferably less than 50g, most preferably less than 30g. It has also been found that the collective discharge chute 40 is particularly advantageous for articles having a maximum dimension of less than 5cm, preferably less than 3cm, more preferably less than 2cm, most preferably less than 1 cm. Reducing bouncing and scattering is also particularly important for articles comprise a particulate coating, as such articles have an increased chance of disintegrating when received by a collective discharge chute.

Claims

1. A computer combination weighing apparatus, comprising:a plurality of weighing hoppers; anda collective discharge chute positioned below the plurality of weighing hoppers, wherein the collective discharge chute comprises a flexible substrate having a first surface and an opposed second surface, wherein the first surface of the substrate is arranged to receive articles dispensed from the plurality of weighing hoppers, wherein the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 10 Pa m3 and wherein the second surface of the substrate is arranged to face an air space such that the substrate is configured to flex into the air space in response to articles being received by the first surface of the substrate.

2. The computer combination weighing apparatus of claim 1, wherein the substrate comprises plastic.

3. The computer combination weighing apparatus of claim 2, wherein the plastic is polyvinyl chloride.

4. The computer combination weighing apparatus of any preceding claim, wherein the substrate is transparent.

5. The computer combination weighing apparatus of any preceding claim, wherein the flexural rigidity of the substrate at 20°C and 101.325 kPa is less than 5 Pa m3, preferably less than 2 Pa m3, more preferably less than 1 Pa m3, most preferably less than 0.5 Pa m3.

6. The computer combination weighing of any preceding claim, wherein the flexural rigidity of the substrate at 20°C and 101.325 kPa is greater than 0.0001 Pa m3 preferably greater than 0.001 Pa m3, more preferably greater than 0.005 Pa m3, most preferably greater than 0.01 Pa m3.

7. The computer combination weighing apparatus of any preceding claim, wherein the thickness of the substrate is at most 5 mm, preferably at most 4 mm, more preferably at most 3 mm, most preferably at most 2 mm.

8. The computer combination weighing apparatus of any preceding claim, wherein the Young’s modulus of the substrate at 20°C and 101.325 kPa is less than 15 GPa, preferably less than 10 GPa, more preferably less than 5 GPa, most preferably less than 3GPa.

9. The computer combination weighing apparatus of any preceding claim, wherein the substrate comprises a first layer and a second layer, the first layer comprising a first material and the second layer comprising a different second material.

10. The computer combination weighing apparatus of any preceding claim, wherein the collective discharge chute further comprises a rigid chute portion, wherein the rigid chute portion has a flexural rigidity that is greater than the flexural rigidity of the substrate, and wherein the substrate is coupled to the rigid chute portion.

11. The computer combination weighing apparatus of claim 10, wherein the air space is located between the substrate and the rigid chute portion.

12. The computer combination weighing apparatus of claim 11, wherein the substrate is arranged to be substantially coextensive with the rigid chute portion.

13. The computer combination weighing apparatus of claim 10 or claim 11, wherein the substrate and the rigid chute portion are arranged such that an upper section of the collective discharge chute and a lower section of the collective discharge chute are provided by the substrate and the rigid chute portion respectively.

14. The computer combination weighing apparatus of any of claims 10 to 13,wherein the rigid chute portion comprises metal.

15. The computer combination weighing apparatus of claim 14, wherein the metal is steel.

16. The computer combination weighing apparatus of any preceding claim, wherein the first surface defines a substantially parabolic surface.

17. A method of operating a computer combination weighing apparatus, theapparatus comprising a plurality of weighing hoppers and a collective discharge chute positioned below the plurality of weighing hoppers, the collective discharge chute comprising a flexible substrate having a first surface and an opposed second surface, the first surface of the substrate being arranged to receive articles dispensed from the plurality of weighing hoppers, and the flexural rigidity of the substrate at20°C and 101.325 kPa being less than 10 Pa m3, wherein the method comprises:dispensing articles from the plurality of weighing hoppers;receiving the articles by the first surface of the substrate, wherein the second surface of the substrate is arranged to face an air space such that the substrate flexes into the air space in response to articles being received by the first surface of the substrate.

18. The method of claim 17, wherein dispensing the articles from the plurality of weighing hoppers comprises:dispensing the articles from the plurality of weighing hoppers in batches of less than 200g, preferably less than 100g, more preferably less than 50g, most preferably less than 30g.

19. The method of claim 17 or claim 18, wherein the articles comprise one or more of: crisps; popcorn; nuts; seeds; dried fruits; confectionery; and breaded products.

20. The method of any of claims 17 to 19, wherein each article weighs less than 10g, preferably less than 5g, more preferably less than 2g, most preferably less than 1g.

21. The method of any claims 17 to 20, wherein each article has a maximum dimension of less than 5cm, preferably less than 3cm, more preferably less than 2cm, most preferably less than 1 cm.

22. The method of any of claims 17 to 21, wherein the articles comprise a 5 particulate coating.

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