Weighing apparatus

Abstract

A computer combination weigher (CCW) (fig 1) having a weigh container i.e. weigh hopper with an associated load cell. The load cell is calibrated via tare weight or zero-balancing and a first weight v

Description

FIELD OF THE INVENTION The invention relates to a weighing apparatus, such as a computer combination weighing apparatus. The invention also relates to a method of controlling a 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 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. The weighing hoppers in a CCW typically use load cells to measure the weight of product. A load cell is a sensor which converts an applied force into a signal that can be measured to determine the weight of product held by the weighing unit. During operation of a CCW, the CCW will tend to heat up which causes the zero point of each load cell to undergo thermal drift. It is possible to compensate for this thermal drift by regularly resetting the zero point of each load cell during operation, e.g. by measuring the signal output by each load cell immediately following the discharge of product from the associated weighing hopper and updating the zero point based on this “no-load” signal. Resetting the zero point in this manner also compensates for the presence of any dirt or product which adheres to the weighing hoppers during operation. However, if a CCW pauses for an extended period of time, the zero point of each load cell will also undergo thermal drift due to cooling of the CCW. As the zero point of each load cell is only reset following the discharge of product during operation, this means that the weight of product calculated upon resumption of operation will often be inaccurate. This has been found to negatively impact the control of CCWs, e.g. inaccurate combinations of product may be dispensed from the weighing hoppers leading to increased wastage and giveaway. Accordingly, an object of the present invention is to address this problem. It will be appreciated that this problem is not limited to CCWs and also applies to other types of weighing apparatus which utilise load cells. SUMMARY OF INVENTION According to a first aspect of the invention, there is provided a weighing apparatus comprising: a weighing element configured to receive and hold articles; a load cell associated with the weighing element, wherein the load cell is configured to generate weigh signals based on the weight of articles held by the weighing element; and a control unit communicatively coupled to the load cell, wherein the control unit is configured to: control, in a first mode of operation, at least one aspect of the weighing apparatus based on a first weight value calculated based on a zero point of the load cell and a first weigh signal that is generated by the load cell substantially at the time of the control; when operation of the weighing element is paused, store, in a storage unit, a second weight value calculated based on the zero point of the load cell and a second weigh signal that is generated by the load cell before operation of the weighing element is resumed; and when operation of the weighing element is resumed, control, in a second mode of operation, at least one aspect of the weighing apparatus based on the stored second weight value. In this way, by utilising the stored second weight value to control the weighing apparatus upon resumption of operation, it is ensured that the weighing apparatus is controlled based on a weight value which more accurately reflects the weight of articles held by the weighing element, compared to previous methods. For example, if the weighing apparatus is a computer combination weighing apparatus, it is ensured that the weight values of articles used for combinatorial calculations are more accurate, such that the correct amount of articles can be discharged from the computer combination weighing apparatus. In contrast, for example, following resumption of operation for a conventional computer combination weighing apparatus, the apparatus will be controlled based on a weight value calculated using a previously determined zero point of the load cell and a weigh signal generated by the load cell at the time of control. As the computer combination weighing apparatus will have cooled in temperature during the pause in operation, the (true) zero point will have shifted meaning that the weight value calculated based on the predetermined zero point will be inaccurate. This can result in inaccurate combinations of product being dispensed by the computer combination weighing apparatus. The invention overcomes this issue by, following resumption in operation of the weighing element, controlling the apparatus based on the stored second weight value which is calculated and stored prior to resumption. The second weight value calculated before operation is resumed will more accurately reflect the weight of articles held by the weighing element compared to a weight value that is calculated using the previously determined zero point and the current weigh signal upon resumption, as further cooling of the weighing apparatus will take place by the time that operation is resumed. This means that by using the second weight value to control the apparatus when operation is resumed, the apparatus can be controlled based on a more accurate weight value of articles and the impact of zero point thermal drift will be lessened. It will be understood by the skilled person that the weigh signal output by the load cell is proportional to the force applied to the load cell, which includes the weight of the weighing element itself and the weight of articles held by the weighing element. Hence, the zero point of the load cell refers to an offset which can be applied to the weigh signal to enable calculation of the weight of the articles held by the weighing element only. The zero point is determined by measuring the weigh signal output by the load cell when the weighing element is not holding any articles, e.g. following discharge of articles from the weighing element but prior to any new articles being received by the weighing element. The zero point may also be referred to as a zero balance, a zero offset, or a zero point value. It will also be understood by the skilled person that “substantially at the time of the control” means at the same time or slightly before the time of control, e.g. no more than 0.01, 0.05, 0.1,0.5 or 1 second before the time of control. Preferably, the second weigh signal is generated by the load cell no later than 60 seconds after pausing, preferably no later than 30 seconds, more preferably no later than 10 seconds, most preferably no later than 5 seconds after pausing. More preferably, the second weigh signal is generated by the load cell substantially at or before the time of pausing. In other words, the second weight value may be calculated prior to any cooling of the weighing apparatus such that the predetermined zero point remains appropriate to use and the second weight value therefore accurately represents the weight of articles held by the weighing element. This means that any thermal shift in the (true) zero point which occurs during the pause in operation will not have any impact on the control of the weighing apparatus when operation is resumed. It will be understood that the second weight value relates to articles held by the weighing element at the time of the pause. More preferably, the second weigh signal is generated by the load cell substantially at the time of pausing. It will be understood by the skilled person that “substantially at the time of pausing” means at the same time or slightly before or slightly after the time pausing, e.g. no more than 0.01,0.05, 0.1,0.5 or 1 second before or after the time of pausing. A particularly preferred form of weighing unit is a weighing hopper. It will be appreciated that the storage unit is a data storage unit which may form part of the weighing apparatus or may be located remotely with respect to the weighing apparatus. Preferably, controlling in the first mode of operation at least one aspect of the weighing apparatus based on the first weight value comprises: causing the weighing element to discharge the articles held by the weighing element based on the first weight value, and controlling in the second mode of operation at least one aspect of the weighing apparatus based on the second stored weight value comprises: causing the weighing element to discharge the articles held by the weighing element based on the stored second weight value. Preferably, the weighing apparatus is a computer combination weighing apparatus, and controlling in the first mode of operation at least one aspect of the weighing apparatus based on the first weight value comprises: performing one or more first combinatorial calculations based on the first weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus; based on the one or more first combinatorial calculations, identifying a first selection of weighing elements holding articles having a combined weight meeting one or more requirements with respect to a first target weight; and causing the weighing element to discharge the articles held by the weighing element in response to determining that the first selection includes the weighing element, and controlling in the second mode of operation at least one aspect of the weighing apparatus based on the stored second weight value comprises: performing one or more second combinatorial calculations based on the second weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus; based on the one or more second combinatorial calculations, identifying a second selection of weighing elements holding articles having a combined weight meeting one or more requirements with respect to a second target weight; and causing the weighing element to discharge the articles held by the weighing element in response to determining that the second selection includes the weighing element. In one embodiment, the one or more requirements with respect to the first target weight may comprise at least one of: the combined weight of articles held by the first selection of weighing elements being within a threshold of the first target weight; and the combined weight of articles held by the first selection of weighing elements being closer to the first target weight than a combined weight of articles held by each other selection of weighing elements. Similarly, the one or more requirements with respect to the second target weight may comprise at least one of: the combined weight of articles held by the second selection of weighing elements being within a threshold of the second target weight; and the combined weight of articles held by the second selection of weighing elements being closer to the second target weight than a combined weight of articles held by each other selection of weighing elements. It will be understood that the computer combination weighing apparatus comprises a plurality of weighing elements and associated load cells, each configured to be controlled by the control unit in a corresponding manner to the weighing element of the first aspect. In this regard, it should be noted that switching between the first and second modes of operation for each weighing element may be independent. For example, generally, before a pause all weighing elements will be operating in the first mode of operation and immediately upon resuming after a pause all weighing elements will be operating in the second mode of operation; however, individual weighing element may switch back from the second mode of operation to the first mode of operation at different times, depending on the nature of the control of the computer combination weighing apparatus. For example, in some embodiments, the second mode of operation is used only while the weighing element holds the articles that were held at the time of the pause, and so as each weighing element discharges its articles, it will switch back to the first mode of operation. Preferably, the control unit is configured to switch from the first mode of operation to the second mode of operation in response to: operation of the weighing element being paused; or operation of the weighing element being resumed. Preferably, the control unit is configured to switch from the second mode of operation to the first mode of operation in response to at least one of: determining that articles have been discharged from the weighing element; determining that the zero point of the load cell has been reset; determining that a threshold amount of time has passed since resumption of operation of the weighing element; and determining that a threshold number of controls have been performed using the weighing element. It will be understood that determining that articles have been discharged by the weighing element comprises determining that the articles held by the weighing element during the pause in operation have been discharged from the weighing element. In some embodiments, the control unit switches from the second mode of operation to the first mode of operation once the articles held by the weighing element at the time of the pause are dispensed, with any subsequent articles received by the weighing element being handled in accordance with the first mode. However, in other embodiments, the second mode of operation may continue for subsequent articles received by the weighing element, as will be described in more detail below, with a return to the first mode occurring only once the zero point of the load cell has been reset or after it is determined that the apparatus has been resumed long enough to counteract any thermal drift. In this way, the control unit stops using the stored second weight value for controlling the weighing apparatus once it becomes more appropriate to use a weight value calculated based on the current weigh signal. For example, once the zero point of the load cell is reset, i.e. determined based on a weigh signal output by the load cell following discharge of articles from the weighing element, the current weigh signal in combination with the reset zero point can be used to accurately calculate the weight of articles held by the weighing element. In addition, once a threshold amount of time has passed or number of controls has been performed since resumption of operation of the weighing element, the weighing element may have heated up to a temperature similar to the temperature of the weighing element prior to the pause in operation, such that accurate weight values can once again be calculated based on the current weigh signal and the previously determined zero point. In one embodiment, controlling in the second mode of operation at least one aspect of the weighing apparatus based on the second stored weight value comprises: controlling at least one aspect of the weighing apparatus independently of the weigh signal generated by the load cell substantially at the time of control. In other words, control of the weighing apparatus in the second mode of operation in respect of articles held by the weighing element during the pause in operation is not dependent on the current weigh signal output by the load cell. For example, when the weighing apparatus is a computer combination weighing apparatus, the one or more first combinatorial combinations may be performed by summing the first weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus, and the one or more second combinatorial combinations may be performed by summing the second weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus. It will be appreciated that this method of controlling the apparatus independently of the weigh signal generated by the load cell substantially at the time of control may only be used for first articles that were in the or each weighing element at the time of the pause, i.e. whilst the weighing element is holding articles associated with the stored second weight value. Once the or each weighing element has discharged that first articles and received new articles, the weigh signal generated by the load cell will need to be used; however, this can be adjusted based on the weigh signals generated before and after the pause, as will be described below. In particular, controlling in the second mode of operation at least one aspect of the weighing apparatus based on the second stored weight value may further comprise: calculating an adjusted zero point of the load cell based on the stored second weight value and a third weight value calculated based on the zero point of the load cell and a third weigh signal that is generated by the load cell after the second weigh signal, wherein preferably the third weigh signal is generated by the load cell substantially at or after the time of the resumption, the second and third weight values relating to articles held by the weighing element at the time of the pause; and controlling at least one aspect of the weighing apparatus based on a fourth weight value, wherein the fourth weight value is calculated based on the adjusted zero point of the load cell and a fourth weigh signal that is generated by the load cell substantially at the time of the control. In these embodiments, the second mode of operation may be used for one or more sets of articles after the resumption by adjusting the zero point to account for any observed drift. In this case, control of the weighing apparatus depends on the stored second weight value and the current weigh signal output by the load cell, i.e. the weigh signal output by the load cell substantially at the time of control. For example, when the weighing apparatus is a computer combination weighing apparatus, one or more combinatorial combinations may be performed by summing the fourth weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus. It will be appreciated that the fourth weight value may relate to subsequent articles received and held by the weighing element after the articles held by the weighing element during the pause in operation have been discharged by the weighing element or, alternatively, may relate to articles held by the weighing element at the time of pausing. In one embodiment, calculating an adjusted zero point of the load cell may comprise calculating the adjusted zero point based on the difference between the stored second weight value (for example, obtained substantially at or before the time of the pause) and the third weight value (for example, obtained substantially at the time of resumption). In this way, a single adjustment of the zero point may be performed upon resumption to account for any drift observed during the pause. In another embodiment, the adjusted zero point may be iteratively calculated, e.g. during the pause. For example, an intermediary adjusted zero point may be calculated based on the difference between the stored second weight value and an intermediary weight value calculated based on the zero point of the load cell and an intermediary weigh signal that is generated by the load cell during the pause in operation, and the adjusted zero point may be calculated based on the difference between the second intermediary weight value and the third weight value. It will be appreciated that the number of intermediary adjusted zero points may vary. Preferably, the third weigh signal is generated by the load cell no later than 0.1, 0.5, 1, 2, 5 or 10 seconds after resumption. Notably, the third weigh signal is generated before the weighing element discharges the articles held by the weighing element during the pause in operation. It will be understood that the adjusted zero point is a temporary zero point, and will not be used when the control unit switches to the first mode of operation. For example, the adjusted zero point may be replaced upon a zero point reset operation. Preferably, the control unit is configured to: after operation of the weighing element is paused, schedule the zero point of the load cell to be reset dependent on the duration of the pause. The level of cooling of the weighing apparatus will depend on the duration of the pause in operation, i.e. a longer pause will be accompanied by greater cooling of the load cell. This means that the drift in the zero point will be greaterfor longer pauses, such that the urgency to reset the zero point will also be greater. For a shorter pause, the cooling of the load cell may not be particularly significant, such that it may be appropriate to use the previously determined zero point shortly after resumption. Hence, by scheduling the zero point to be reset based on the length of time that operation of the weighing element is paused, it is ensured that weight values can be accurately calculated when the control unit switches back to the first mode of operation. Preferably, the control unit is configured to: after operation of the weighing element is paused, schedule the zero point of the load cell to be reset dependent on the duration of the pause and the number of times that articles have been discharged from the weighing element since the last time that the zero point of the load cell was reset. In this way, adhesion of articles to the weighing element and other changes to the zero balance force applied to the load cell which arise during normal operation are also taken into account when scheduling the reset. In one example, the control unit may be configured to: when operation of the weighing apparatus is paused, increment a counter stored in the storage unit based on the length of the time that operation of the weighing element has been paused; and in response to determining that the counter exceeds a threshold count, schedule a zero point reset for the load cell. The control unit may be further configured to: in response to determining that articles have been discharged from the weighing element, increment the counter. Preferably, the control unit is configured to schedule the zero point of the load cell to be reset at a timing after articles are next discharged from the weighing element and before articles are next received by the weighing element. In one embodiment, the control unit is configured to: when operation of the weighing element is paused, monitor the weigh signals generated by the load cell; and in response to determining that weight values calculated from the monitored weigh signals exceed a threshold fluctuation in weight values, switch to the first mode of operation. A small gradual change in the weigh signals during the pause in operation would be expected due to thermal drift, but a sudden or significant change in the weigh signals may be indicative of the amount of articles in the weighing apparatus changing, e.g. due to tampering. In the latter case, the saved weight value can no longer be trusted. Hence, by switching to the first mode of operation if a threshold fluctuation is detected, it is ensured that the second stored weight value is only used for controlling the weighing apparatus if the amount of articles held by the weighing element remains unchanged during the pause in operation. In one example, the threshold fluctuation may refer to an absolute variation in the magnitude of the weight values. In another example, the threshold fluctuation may refer to a relative variation in the magnitude of the weight values. In another example, the threshold fluctuation may refer to a rate of change in the magnitude of the weight values. Preferably, the control unit is further configured to: in response to determining that weight values calculated from the monitored weigh signals exceed the threshold fluctuation in weight values, delete the stored second weight value from the storage unit. In another embodiment, the control unit is configured to: when operation of the weighing apparatus is paused, monitor the weigh signals generated by the load cell; and in response to determining that weight values calculated from the monitored weigh signals exceed a threshold fluctuation in weight values, update the stored second weight value based on the monitored weigh signal. In this way, the stored second weight value may be updated to accurately reflect the weight of articles held by the weighing element, such that it remains appropriate for the control unit to operate in the second mode of operation upon resumption. For example, if the stored second weight value is 10 g, monitoring of the weigh signals may reveal a slow drift of this value down to 9 g, caused by thermal drift, followed by an abrupt jump to 11 g, caused by the weigh element receiving an additional 2 g of material. In this case, the stored second weight value may be updated to 12 g based on the monitored weigh signals exceeding a threshold fluctuation in weight values. In one example, the threshold fluctuation may refer to an absolute variation in the magnitude of the weight values. In another example, the threshold fluctuation may refer to a relative variation in the magnitude of the weight values. In another example, the threshold fluctuation may refer to a rate of change in the magnitude of the weight values. Preferably, the control unit is configured to: store the second weight value in response to receiving a pause command; or store the second weight value in response to determining that the weighing element has been idle for a threshold time. For example, the weighing element may not have received and / or dispensed articles for the threshold time. In this way, it is possible to compensate for thermal drift of the zero point in the case of a deliberate pause in operation and in the case of a pause in operation caused by a low supply of articles. Preferably, the apparatus is a computer combination weighing apparatus. It will be appreciated that a computer combination weighing apparatus may also be referred to as a computer combination weigher or a multihead weigher. According to a second aspect of the invention, there is provided a method of controlling a weighing apparatus, wherein the weighing apparatus comprises a weighing element and a load cell associated with the weighing element, wherein the load cell is configured to generate weigh signals based on the weight of articles held by the weighing element, the method comprising: controlling, in a first mode of operation, at least one aspect of the weighing apparatus based on a first weight value calculated based on a zero point of the load cell and a first weigh signal that is generated by the load cell substantially at the time of controlling; when operation of the weighing element is paused, storing, in a storage unit, a second weight value calculated based on the zero point of the load cell and a second weigh signal that is generated by the load cell before operation of the weighing element is resumed; when operation of the weighing element is resumed, controlling, in a second mode of operation, at least one aspect of the weighing apparatus based on the stored second weight value. Preferably, wherein the method further comprises method steps corresponding to one or more of the actions which the control unit of the first aspect is configured to perform. 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 shown in Figure 1; Figure 3 is a flow diagram illustrating an exemplary method for operating the computer combination weighing apparatus of Figure 1; Figure 4 is a flow diagram illustrating a method for operating a weighing apparatus according to the invention; Figure 5A is a flow diagram illustrating a method of controlling an aspect of the weighing apparatus that may be implemented as part of the method of Figure 4; Figure 5B is a flow diagram illustrating a method of controlling an aspect of the weighing apparatus that may be implemented as part of the method of Figure 4; Figure 6 is a flow diagram illustrating a method of resetting the zero point of a weighing element that may be implemented as part of the method of Figure 4; Figure 7 is a flow diagram illustrating a method of monitoring fluctuations in weight values that may be implemented as part of the method of Figure 4; Figure 8 is a flowchart illustrating a method of adjusting the zero point that may be implemented as part of the method of Figure 4; and DETAILED DESCRIPTION An exemplary apparatus which may be configured to operate in accordance with the present invention will first be described with reference to Figures 1 and 2. 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 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 and the operation parameters of the motor used to transport the food product P. The controller 50 may be communicatively coupled to a storage unit 45 for storing operational parameters and weight values. 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 a discharge chute, which brings all product to a common discharge point 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 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. The controller will also cause the feeders 11 to feed new product into the pool hoppers 20 that were just emptied. The controller will then repeat the process with the set of partial batches in the weighing hoppers 30. This weighing operation will now be described in further detail with reference to method 300 illustrated in the flowchart of Figure 3. The method 300 begins at step 302 in which product P (also referred to as articles) is received by the weighing hoppers 30. Specifically, each weighing hopper 30 that has just been discharged receives a new batch of product P from the corresponding pool hopper 20. At step 304, the weight of articles in each weighing hopper 30 is calculated by the controller 50. In particular, each load cell 32 outputs a weigh signal that is proportional to the force applied to the load cell 32, and weight values of product P in each weighing hopper 30 are calculated using the respective weigh signal and a predetermined zero point of the respective load cell 32. The zero point may also be referred to as a zero offset or zero balance, and will be understood to refer to a weight value offset determined by measuring a weigh signal output by the load cell 32 when the corresponding weighing hopper 30 does not contain a batch of product P. At step 306, the controller 50 performs a number of combinatorial calculations based on the weight values of product P in different selections of weighing hoppers 30. For example, a first weighing hopper may hold product P having a weight value of 30g, a second weighing hopper may hold product P having a weight value of 20g, and a third weighing hopper may hold product P having a weight value of 35g. A combinatorial calculation based on this selection of weighing hoppers would result in a calculated combined weight of 85g. At step 308, product P is dispensed from a particular selection of weighing hoppers 30 which meet a predetermined weight criteria. For example, the predetermined weight criteria may include: the combined weight of product P held by the particular selection of weighing hoppers being within a threshold of a target weight, and / or the combined weight of product P held by the particular selection of weighing hoppers being closest to the target weight compared with all other selections of weighing hoppers. At step 310, the controller 50 checks whether any of the discharged weighing hoppers 30 meet criteria for resetting the zero point of the corresponding load cell 32. For example, the criteria may be that the weighing hooper 30 has been discharged at least a threshold number of times. At step 312, the zero point of each load cell 32 corresponding to each weighing hopper 32 that meets the criteria is reset. The reset is performed based on measuring the weigh signal output by the respective load cell 32 before new product P is fed to the weighing hopper 30. After the zero point has been reset for each applicable load cell 32, the method 300 restarts at step 302. This method of operation compensates for changes in the zero point of each load cell 32 which occur during operation of the combination weighing apparatus 10, for example changes related to thermal drift of the load cell 32 or matter adhering to the weighing hoppers 30. However, it has been found the zero point may also thermally drift whilst operation of the combination weighing apparatus 10 is paused, due to each load cell 32 cooling down whilst the combination weighing apparatus 10 is idle. This means that when operation of the combination weighing apparatus 10 is restarted, the weight value calculated based on the predetermined zero point (also referred to as the stored zero point value) in combination with the current weigh signal output by the load cell 32 will not accurately reflect the weight of product P in the weighing hopper 32. As a consequence, controlling the combination weighing apparatus 10 based on this (inaccurately) calculated weight value may be inappropriate. A method 400 of controlling a weighing apparatus which addresses this issue will now be described with reference to the flowchart illustrated in Figure 4. The present description of this method 400 will focus on the operation of a single weighing hopper 30 and its associated load cell 32, but it will be appreciated that the process will be occurring in parallel for each weighing hopper 30 and associated load cell 32 within the weighing apparatus. The method will be described with reference to the computer combination weighing apparatus 10, but it will be appreciated that the method 400 is not limited to this type of combination weighing apparatus and can equally be applied to other types of weighing apparatus comprising at least one weighing element and an associated load cell. The method 400 starts at step 402, during which the controller 50 is operating according to a first mode of operation. In the first mode of operation, the controller 50 controls at least one aspect of the weighing apparatus 10 based on a first weight value that is calculated based on a first weigh signal which is output by the load cell 32 substantially at the time of the control. It will be understood by the skilled person that “substantially at the time of the control” means at the same time as the time of control or slightly before the time of control, e.g. 0.01,0.05, 0.1, 0.5, or 1 second before the time of control. In other words, in the first mode of operation, the weighing apparatus 10 is controlled according to the current weigh signal output by the load cell 32. The first mode of operation may be considered to be a normal mode of operation, for example corresponding to the method of Figure 3. The first weight value is calculated using the first weigh signal in combination with a predetermined zero point of the load cell 32. The zero point will have been determined at previous time when a batch of product P was not present in the weighing hopper 30 associated with the load cell 32, e.g. as previously described with reference to Figure 3. In the presently described case in which the weighing apparatus 10 is a computer combination weighing apparatus, an example of controlling an aspect of the weighing apparatus 10 based on the first weight value is now described with reference to Figure 5A. At step 502, the controller 50 uses the first weight value and other weight values indicative of the weight of product P in other weighing hoppers of the computer combination weighing apparatus 10 to perform first combinatorial calculations, e.g. as previously described with reference to step 306 of Figure 3. In particular, the first weight value and other weight values are added together to calculate combined weights for a number of different selections of weighing hoppers. At step 504, the controller 50 identifies a first selection of weighing hoppers which are holding product P with a combined weight which meets one or more requirements with respect to a first target weight. In response to determining that the first selection includes the weighing hopper 30, the controller 50 then causes the weighing hopper 30 to discharge the product P held by the weighing hopper 30. This is described in further detail with reference to step 308 of Figure 3. Returning to the method 400, at step 404 the operation of the weighing hopper 30 (or weighing apparatus 10 in general) is paused. This may refer to a situation in which a pause command or power off command is received by the controller 50, or may refer to a scenario in which the weighing hopper 30 or weighing apparatus 10 has been idle for a threshold amount of time. At step 404, in response to determining that operation of weighing hopper 30 or weighing apparatus 10 is paused, the controller 50 stores a second weight value in the storage unit 45 of the weighing apparatus 10. The second weight value is calculated based on the previously determined zero point and a second weigh signal that is output by the load cell 32 associated with the weighing hopper 30 substantially at the same time as pausing. It will be understood that “substantially at the time of pausing” means at the same time as the time of pausing or slightly before or slightly after the time pausing, e.g. 0.01,0.05, 0.1,0.5, or 1 second before or after the time of pausing. In other words, the second weight value is calculated based on the current weigh signal output by the load cell 32 when operation is paused. At step 408, operation of the weighing hopper 30 (or weighing apparatus 10 in general) is resumed. This may refer to a situation in which a restart command or power on command is received by the controller 50, or may refer to an idle state of the weighing hopper 32 or weighing apparatus 10 ending. Next, at step 410, the controller 50 switches to operating according to a second mode of operation. This switch in operational mode may be performed in response to determining that operation of the weighing hopper 30 or weighing apparatus 10 has been resumed, as illustrated in Figure 4. Alternatively, the controller 50 may switch to the second mode of operation in response to determining that operation of the weighing hopper 30 or weighing apparatus 10 has been paused, i.e. prior to the resumption of operation. In the second mode of operation, at step 412 the controller 50 controls at least one aspect of the weighing apparatus 10 based on the stored second weight value. This means that any zero point drift of the load cell 32 which has occurred during the pause in operation will not affect control of the weighing apparatus 10, as the weighing apparatus 10 is controlled according to the stored second weight value rather than being controlled according to a weight value calculated based on the current weigh signal and previously determined zero point. In other words, the weigh signal output by the load cell 32 at the time of control in step 412 is ignored when controlling the weighing apparatus 10 in the second mode of operation. This second mode of operation relies on the assumption that the second stored weight value is indicative of the current weight of product P in the weighing hopper 32 upon resumption, i.e. that the amount of product P remains unchanged during the pause in operation. In the presently described case in which the weighing apparatus 10 is a computer combination weighing apparatus, an example of controlling an aspect of the weighing apparatus 10 based on the stored second weight value is described with reference to Figure 5B. At step 508, the controller 50 uses the stored second weight value and other weight values indicative of the weight of product P in other weighing hoppers of the computer combination weighing apparatus 10 to perform second combinatorial calculations, e.g. as previously described with reference to step 306 of Figure 3. In particular, the stored second weight value and other weight values are added together to calculate combined weights for various different selections of weighing hoppers 30. At step 510, the controller 50 identifies a second selection of weighing hoppers which are holding product P with a combined weight which meets one or more requirements with respect to a second target weight. In response to determining that the second selection includes the weighing hopper 30, the controller 50 then causes the weighing hopper 30 to discharge product P from the weighing hopper 30. This is described in further detail with reference to step 308 of Figure 3. Returning to the method 400, at step 414 the controller 50 determines whether to switch back to the first mode of operation. In a first example, the controller 50 switches to the first mode of operation in response to determining that product P has been discharged from the weighing hopper 30. Once product P has been discharged from the weighing hopper 30, it would be inappropriate to use the second stored weight value to control the weighing apparatus 10 as the second stored weight value is indicative of the weight of product P that is no longer present in the weighing hopper 30. In a second example, the controller 50 switches to the first mode of operation in response to determining that the zero point of the load cell 32 has been reset. Once the zero point of the load cell 32 has been reset, the current weigh signal can be used to reliably calculate the weight of articles held by the weighing hopper 30 in combination with the reset zero point, such that it is appropriate to operate according to the first mode of operation. Resetting the zero point is performed based on measuring the weigh signal output by the load cell 32 immediately following the discharge of product P from the weighing element 30. In a third example, the controller 50 switches to the first mode of operation in response to determining that a threshold amount of time has passed since resumption of operation of the weighing hopper 30 or weighing apparatus 10. Once a threshold amount of time has passed since resumption, the weighing hopper 30 will have increased in temperature enough to substantially reverse the thermal drift of the zero point, such that accurate weight values can once again be calculated based on the current weigh signal and the previously determined zero point. Hence, it becomes appropriate for the controller 50 to operate according to the first mode of operation. When the controller 50 has switched to the first mode of operation, the method 400 restarts at step 402, wherein the controller 50 controls at least one aspect of the weighing apparatus 10 based on a (new) first weight value calculated based on the current weigh signal. Advantageously, by using the stored second weight value to control the weighing apparatus 10 upon resumption of operation, rather than using a weight value calculated based on the current weigh signal and the previously determined zero point, it is ensured that any thermal drift in the zero point during the pause in operation does not impact control of the weighing apparatus 10. Although in this embodiment it has been described that the second weigh signal is generated by the load cell 32 substantially at the time of pausing, more generally the second weigh signal used for calculating the second weight value may be generated by the load cell 32 before operation of the weighing element is resumed. However, it will be appreciated that the calculated second weight value may decrease in accuracy as the time between pausing and generating the second weigh signal increases, due to further thermal drift of the zero point of the load cell 32. Next, a method 600 of resetting the zero point of the weighing hopper 30 will be described with reference to Figure 6. The method 600 can be implemented as part of method 400. The method 600 begins at step 602 when operation of the weighing hopper 30 or weighing apparatus 10 is paused, corresponding to step 602 of method 400. At step 604, during the pause in operation, the controller 50 checks whether criteria for scheduling the zero point of the load cell 32 to be reset are met. For example, the criteria may comprise or consist of whether operation of the weighing hopper 30 or weighing apparatus 10 has been paused fora threshold amount of time. If the controller 50 determines that the criteria has been met, at step 606 the controller 50 schedules the predetermined zero point of the load cell 32 to be reset. The reset of the zero point is scheduled for a timing after the weighing hopper 30 has next been discharged and before new product P has been fed to the weighing hopper 30. In other words, the zero point reset is scheduled for the next timing at which the weighing hopper 30 is not holding a batch of product P. At step 608, operation of the weighing hopper 30 or weighing apparatus 10 is restarted, and at step 610 the weighing hopper 30 is discharged, e.g. in accordance with the previously described methods. In response to the weighing hopper 30 being discharged, at step 612 the controller 50 determines whether a zero point reset is scheduled. If so, at step 614 the zero point of the load cell 32 is reset. In particular, the zero point is reset based on the weigh signal output by the load cell 32 prior to new product P being received by the weighing hopper 30. The temperature decrease of the weighing apparatus 10 during the pause in operation is dependent on the duration of the pause. Therefore, by scheduling a zero point reset based on the duration of the pause it is ensured that the zero point of the load cell 32 is reset as soon as possible in the case of significant thermal drift of the zero point which occurs for longer pause durations. For shorter pause durations, the temperature decrease will be small such that the temperature of the weighing apparatus 10 may reach normal operational levels again soon after resuming operation. Hence, in this case, an urgent zero point reset is not required. As discussed above with reference to Figure 3, the zero point may also be scheduled to be reset during operation of the weighing apparatus 10. For example, the controller 50 may schedule or cause the zero point of the load cell 32 to be reset based on the number of times that the weighing hopper 32 has been discharged. The greater the number of discharges, the more likely that matter has adhered to the weighing hopper 30 which will result in drift of the zero point. Optionally, at step 604, the controller 50 may therefore schedule the zero point of the load cell 32 to be reset dependent on the duration of the pause and the number of times that the weighing hopper 30 has been discharged. For example, when operation of the weighing apparatus 10 is paused, a counter stored in the storage unit 45 may be incremented based on the length of the time that operation of the apparatus 10 has been paused. The counter may also be incremented during operation in response to determining that product P has been discharged from the weighing hopper 30. At step 604, or alternatively at any time during operation, the controller 50 can then schedule a zero point reset for the load cell 32 in response to determining that the counter exceeds a threshold count. Next, a method 700 of performing remedial action based on monitored weigh signals generated by the load cell 32 will be described with reference to Figure 7. The method 700 can be implemented as part of method 400. The method 700 begins at step 702 wherein operation of the weighing hopper 30 or weighing apparatus 10 is paused. This step 702 corresponds to step 404 in method 400. In response to operation being paused, at step 704 the controller 50 monitors weigh signals generated by the load cell 32. This means that the controller 50 receives and comparatively analyses weigh signals output by the load cell 32 during the pause in operation. At step 706, the controller 50 determines whether there is a fluctuation in the monitored weigh signals which exceeds a threshold fluctuation. In one example, the controller 50 may calculate weight values from each weigh signal, and determine whether there is a threshold fluctuation between the weight values. In another example, the controller 50 may determine whether there is a threshold fluctuation between the raw weigh signals. The threshold fluctuation may refer to an absolute variation in the magnitude of the weight values or amplitude of weigh signals, a relative variation in the magnitude of the weight values or amplitude of weigh signals, or a rate of change in the magnitude of the weight values or amplitude of weigh signals. Detection of a threshold fluctuation is indicative of tampering with the weighing hopper 30 and / or the amount of product P held by the weigh hopper 30 changing during the pause in operation. Hence, in response to detecting a threshold fluctuation, at step 708 the controller 50 performs a remedial action. In a first embodiment, the remedial action may comprise switching to the first mode of operation. Optionally, the stored second weight value may also be deleted from the storage unit 45. In view of the threshold fluctuation, the stored second weight value can no longer be considered representative of the weight of product P in the weighing hopper 30. It follows that it would be inappropriate to operate in the second mode of operation and use the second stored weight value to control the weighing apparatus 10. In a second embodiment, the remedial action may comprise updating the stored second weight value based on the monitored weigh signal. That is, the predetermined zero point is increased or decreased dependent on the level of the fluctuation between the monitored weigh signals or weight values. In this way, the stored second weight value may be updated to accurately reflect the weight of articles held by the weighing hopper 30, such that it is appropriate for control unit 50 to operate in the second mode of operation upon resumption. For example, if the stored second weight value is 10 g, monitoring of the weigh signals may reveal a slow drift of this value down to 9 g, caused by thermal drift, followed by an abrupt jump to 11 g, caused by the weigh element receiving an additional 2 g of material. In this case, the stored second weight value may be updated to 12 g based on the monitored weigh signals exceeding a threshold fluctuation in weight values. In a third embodiment, the remedial action may comprise deactivating the weighing hopper 30 and marking the weighing hopper 30 for inspection. That is, the controller 50 may block further operation of the weighing hopper 30 until the cause behind the fluctuation in weigh signals or weight values has been investigated and addressed. In the above described methods, it has been generally described that in the second mode of operation the controller 50 controls at least one aspect of the weighing apparatus 10 based on the second stored weight value. In this regard, in a first specific embodiment, controlling at least one aspect of the weighing apparatus 10 in the second mode of operation based on the second stored weight value may comprise controlling at least one aspect of the weighing apparatus 10 independently of the current weigh signal generated by the load cell 32, i.e. independently of the weigh signal output by the load cell 32 substantially at the time of control. For example, when the weighing apparatus 10 is a computer combination weighing apparatus as described above, the second combinatorial combinations may be performed by summing the second weight value and the other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus 10. However, it will be appreciated that it is only appropriate to control the weighing apparatus 10 using the second stored weight value and independently of the current weigh signal whilst the weighing hopper 30 is holding the same product P as that held by the weighing hopper 30 at the time of pausing. Once the weighing hopper 30 has discharged the product P that was present in the weighing hopper 30 during the pause in operation and received a new batch of product, the current weigh signal generated by the load cell 32 will need to be used to control the weighing apparatus 10. To this end, when the zero point has not yet been reset and the control unit 50 is still operating in the second mode of operation, for subsequent batches of product P received by the weighing hopper 30 the weighing apparatus 10 may be controlled as described below with reference to Figure 8. Figure 8 is a flowchart illustrating a method 800 which may form part of method 400. In particular, the method 800 begins at step 802 which follows on from method step 410 of method 400. Particularly, at step 410, operation of the weighing hopper 30 or weighing apparatus 10 is resumed and the controller 50 is operating in the second mode of operation. At step 802, the controller 50 calculates an adjusted zero point of the load cell 32 based on the stored second weight value and a third weight value that is calculated based on the predetermined zero point of the load cell 32 and a third weigh signal that is generated by the load cell 32 substantially at the time of the resumption. It will be understood that “substantially at the time of resumption” means at the same time or slightly before or slightly after the time resumption, e.g. 0.01,0.05, 0.1,0.5 or 1 second before or after the time of pausing. However, in a less preferred example, the third weigh signal may be generated by the load cell 32 at or after the time resumption of operation, noting that the third weigh signal must be generated before the weighing hopper 30 dispenses the product P held by the weighing hopper 30 during the pause in operation. In one embodiment, calculating an adjusted zero point of the load cell may comprise calculating the adjusted zero point based on the difference between the stored second weight value and the third weight value. In another embodiment, the adjusted zero point may be iteratively calculated. For example, a first intermediary adjusted zero point may be calculated based on the difference between the stored second weight value and a first intermediary weight value calculated based on the zero point of the load cell and a first intermediary weigh signal that is generated by the load cell during the pause in operation, a second intermediary adjusted zero point may be calculated based on the difference between the first intermediary weight value and a second intermediary weight value calculated based on the first intermediary adjusted zero point of the load cell and a second intermediary weigh signal that is generated by the load cell during the pause in operation, and the adjusted zero point may be calculated based on the difference between the second intermediary weight value and the third weight value. It will be appreciated that the number of intermediary adjusted zero points may vary. At step 804, product P held by the weighing hopper 30 is dispensed and new product P is received by the weighing hopper 30. This may correspond to step 412 of method 400. Subsequently, at step 806, the controller 50 controls at least one aspect of the weighing apparatus 10 based on a fourth weight value. The fourth weight value is calculated based on the adjusted zero point of the load cell 32 and a fourth weigh signal that is generated by the load cell 32 substantially at the time of the control. In this case, control of the weighing apparatus 10 depends both on the stored second weight value and the current weigh signal output by the load cell, i.e. the weigh signal output by the load cell 32 substantially at the time of control. For example, when the weighing apparatus 10 is a computer combination weighing apparatus as described above, combinatorial combinations may be performed by summing the fourth weight value and the other weight values calculated based on other weigh signals associated with other weighing hoppers of the computer combination weighing apparatus. It will be understood by the skilled person that the adjusted zero point is a temporary zero point, and will not be used when the controller 50 switches to the first mode of operation. That is, updating the zero point is not equivalent to resetting the predetermined zero point, as resetting the predetermined zero point requires measuring the weigh signal output by the load cell 32 when the weighing hopper 30 is not holding a batch of product P. The method 800 continues at step 808 which substantially corresponds to step 414 of method 400. Alternatively, in a second specific embodiment, controlling at least one aspect of the weighing apparatus 10 in the second mode of operation based on the second stored weight value may comprise, when the weighing hopper 30 is holding the same product P as that held by the weighing hopper 30 at the time of pausing, controlling at least one aspect of the weighing apparatus based on adjusted zero point and the weigh signal generated by the load cell 32 substantially at the time of control, i.e. the fourth weight value. In this case, the fourth weight value relates to product P held by the weighing hopper during the pause in operation. For example, when the weighing apparatus 10 is a computer combination weighing apparatus as described above, the second combinatorial combinations may be performed by summing the fourth weight value and the other weight values calculated based on other weigh signals associated with other weighing hoppers of the computer combination weighing apparatus 10.

Claims

1. A weighing apparatus comprising:a weighing element configured to receive and hold articles;a load cell associated with the weighing element, wherein the load cell is configured to generate weigh signals based on the weight of articles held by the weighing element; anda control unit communicatively coupled to the load cell, wherein the control unit is configured to:control, in a first mode of operation, at least one aspect of the weighing apparatus based on a first weight value calculated based on a zero point of the load cell and a first weigh signal that is generated by the load cell substantially at the time of the control;when operation of the weighing element is paused, store, in a storage unit, a second weight value calculated based on the zero point of the load cell and a second weigh signal that is generated by the load cell before operation of the weighing element is resumed; andwhen operation of the weighing element is resumed, control, in a second mode of operation, at least one aspect of the weighing apparatus based on the stored second weight value.

2. The weighing apparatus of claim 1, wherein controlling in the first mode of operation at least one aspect of the weighing apparatus based on the first weight value comprises:causing the weighing element to discharge the articles held by the weighing element based on the first weight value, andwherein controlling in the second mode of operation at least one aspect of the weighing apparatus based on the second stored weight value comprises:causing the weighing element to discharge the articles held by the weighing element based on the stored second weight value.

3. The weighing apparatus of claim 1 or claim 2, wherein the weighing apparatus is a computer combination weighing apparatus, and wherein controllingin the first mode of operation at least one aspect of the weighing apparatus based on the first weight value comprises:performing one or more first combinatorial calculations based on the first weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus;based on the one or more first combinatorial calculations, identifying a first selection of weighing elements holding articles having a combined weight meeting one or more requirements with respect to a first target weight; andcausing the weighing element to discharge the articles held by the weighing element in response to determining that the first selection includes the weighing element, andwherein controlling in the second mode of operation at least one aspect of the weighing apparatus based on the stored second weight value comprises:performing one or more second combinatorial calculations based on the second weight value and other weight values calculated based on other weigh signals associated with other weighing elements of the computer combination weighing apparatus;based on the one or more second combinatorial calculations, identifying a second selection of weighing elements holding articles having a combined weight meeting one or more requirements with respect to a second target weight; andcausing the weighing element to discharge the articles held by the weighing element in response to determining that the second selection includes the weighing element.

4. The weighing apparatus of any preceding claim, wherein the control unit is configured to switch from the first mode of operation to the second mode of operation in response to:operation of the weighing element being paused; oroperation of the weighing element being resumed.

5. The weighing apparatus of any preceding claim, wherein the control unit is configured to switch from the second mode of operation to the first mode of operation in response to one of:determining that articles have been discharged from the weighing element;determining that the zero point of the load cell has been reset;determining that a threshold amount of time has passed since resumption of operation of the weighing element; anddetermining that a threshold number of controls have been performed using the weighing element.

6. The weighing apparatus of any preceding claim, wherein controlling in thesecond mode of operation at least one aspect of the weighing apparatus based on the second stored weight value comprises:controlling at least one aspect of the weighing apparatus based on the second stored weight value and independently of the weigh signal that is generated by the load cell substantially at the time of control.

7. The weighing apparatus of any preceding claim, wherein controlling in thesecond mode of operation at least one aspect of the weighing apparatus based on the second stored weight value further comprises:calculating an adjusted zero point of the load cell based on the stored second weight value and a third weight value calculated based on the zero point of the load cell and a third weigh signal that is generated by the load cell after the second weigh signal, the second and third weight values relating to articles held by the weighing element at the time of the pause; andcontrolling at least one aspect of the weighing apparatus based on a fourth weight value, wherein the fourth weight value is calculated based on the adjusted zero point of the load cell and a fourth weigh signal that is generated by the load cell substantially at the time of the control.

8. The weighing apparatus of any preceding claim, wherein the control unit is configured to:after operation of the weighing element is paused, schedule the zero point of the load cell to be reset dependent on the duration of the pause.

9. The weighing apparatus of claim 8, wherein the control unit is configured to:after operation of the weighing element is paused, schedule the zero point of the load cell to be reset dependent on the duration of the pause and dependent on the number of times that articles have been discharged from the weighing element since the zero point of the load cell was last reset.

10. The weighing apparatus of claim 8 or claim 9, wherein the control unit is configured to schedule the zero point of the load cell to be reset at a timing after articles are next discharged from the weighing element and before articles are next received by the weighing element.

11. The weighing apparatus of any preceding claim, wherein the control unit is configured to:when operation of the weighing element is paused, monitor the weigh signals generated by the load cell; andin response to determining that weight values calculated from the monitored weigh signals exceed a threshold fluctuation in weight values, switch to the first mode of operation.

12. The weighing apparatus of claim 11, wherein the control unit is further configured to:in response to determining that weight values calculated from the monitored weigh signals exceed the threshold fluctuation in weight values, delete the stored second weight value from the storage unit.

13. The weighing apparatus of any of claims 1 to 10, wherein the control unit is configured to:when operation of the weighing element is paused, monitor the weigh signals generated by the load cell; andin response to determining that weight values calculated from the monitored weigh signals exceed a threshold fluctuation in weight values, update the stored second weight value based on the monitored weigh signals.

14. The weighing apparatus of any preceding claim, wherein the control unit is configured to:store the second weight value in response to receiving a pause command; orstore the second weight value in response to determining that the weighing element has been idle for a threshold time.

15. The weighing apparatus of any preceding claim, wherein the apparatus is a computer combination weighing apparatus.

16. A method of controlling a weighing apparatus, wherein the weighing apparatus comprises a weighing element and a load cell associated with the weighing element, wherein the load cell is configured to generate weigh signals based on the weight of articles held by the weighing element, the method comprising:controlling, in a first mode of operation, at least one aspect of the weighing apparatus based on a first weight value calculated based on a zero point of the load cell and a first weigh signal that is generated by the load cell substantially at the time of controlling;when operation of the weighing element is paused, storing, in a storage unit, a second weight value calculated based on the zero point of the load cell and a second weigh signal that is generated by the load cell before operation of the weighing element is resumed; andwhen operation of the weighing element is resumed, controlling, in a second mode of operation, at least one aspect of the weighing apparatus based on the stored second weight value.34

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