System and method for sealing food containers

Abstract

A system for sealing a food container, comprising a frame, a first sealing tool mounted to the frame at at least a first mounting location for support by the frame, and a second sealing tool configured to be pressed together to seal a food container located therebetween, and at least one strain gauge mounted to the frame and configured to measure a force transmitted through the frame when the first and second sealing tools are pressed together.

Description

[Technical field]

[0001] The present invention relates to a system and method for sealing food containers, in particular food containers such as food trays and skin sealed trays or sheets, and to the measurement of the sealing pressure generated by such a system and method, in particular to enable the sealing force for each individual tool to be automatically configured to ensure optimal sealing and energy efficiency. [Background technology]

[0002] Systems and methods for sealing food containers often utilize high pressure generated between two sealing tools to seal the container. A specific example of such a system is a tray sealing system, which typically uses heat and pressure to seal a film lid to a tray and seals the film along a sealed seam around the tray. Another example of such a system is a vacuum packing system, which evacuates air between a tray or sheet and a film cover to form a sealed container and then uses heat and pressure to seal a film over the food product along the created seal seam. Summary of the Invention [Problem to be solved by the invention]

[0003] In these processes that use heat and pressure to seal, there are three main factors that affect the quality of the seal: the time the heat and pressure are applied, the temperature used in the sealing process, and the pressure used to create the seal. While time and temperature are easy to measure and control, ensuring sufficient sealing pressure to create a proper seal is much more difficult. Some sealing systems use actuators, such as pneumatic actuators, to press the sealing tools together, which allows the force exerted by the actuator to be directly measured, providing a means to determine the sealing pressure. However, these actuators are typically more complex than others and more expensive to purchase and maintain.

[0004] It would therefore be desirable to provide a system and method for sealing food containers that can monitor the sealing pressure generated during the process of sealing the food container without relying on an actuator for forcing tools together. [Means for solving the problem]

[0005] According to a first aspect of the invention, there is provided a system for sealing food containers, the system comprising a frame, a first sealing tool mounted to the frame at at least a first mounting location for support by the frame, a second sealing tool configured to be pressed together with the first sealing tool to seal a food container located between the first and second sealing tools, and at least one strain gauge mounted to the frame and configured to measure forces transmitted through the frame when the first and second sealing tools are pressed together. An alternative system envisages locating the strain gauge at the first mounting location between the frame and the first sealing tool.

[0006] The system uses at least one sealing tool that is mounted to a frame and supported by it in use, taking advantage of the fact that forces acting on the tool supported by the frame are transferred to the frame. The system uses a strain gauge mounted directly to the frame or at a first mounting point. If the strain gauge is mounted directly to the frame, it can measure the compression, deflection or tension of the frame when forming the seal and measure the sealing pressure. That is, the strain gauge is located at a position on the frame that is compressed, tensioned or deflected when the sealing tools are pressed together. It is particularly preferred to place the strain gauge at a position where the frame is under tension or deflected when the sealing tools are pressed together, as this is more common on a support frame and provides a more accurate reading of the sealing pressure. For example, the strain gauge may be affixed directly to the surface of the frame. The embodiment in which the strain gauge is mounted directly to the surface of the frame is the most cost-effective solution and is particularly preferred. Alternatively, if the strain gauge is located at the first attachment point, it may be part of a load cell located between the first sealing tool and the frame to measure the sealing pressure.

[0007] Although alternative systems are envisaged in which the strain gauge is located at a first attachment point between the frame and the first sealing tool, it is particularly advantageous to attach at least one strain gauge to the frame, particularly to a part of the frame that is subjected to deflection or tension when the sealing tools are pressed together, because the first attachment point where the first sealing tool connects to the frame is routinely manipulated, such as when the sealing tool is removed or replaced, making it easy for the strain gauge to become damaged and require removal and replacement along with the sealing tool.

[0008] As previously mentioned, a single appropriately positioned strain gauge is sufficient to measure the sealing pressure of the system, although in some circumstances multiple strain gauges may be preferred. For example, if the first sealing tool is attached to the frame at multiple mounting locations, it may be preferable to have a strain gauge between the frame and the first sealing tool at each mounting point. Alternatively, if the frame has a pair of beams or columns that deflect when forming a seal, it may be preferable to couple a strain gauge to each location for more accurate measurements.

[0009] It will be appreciated that when the first and second tools are pressed together, the tools may not be in physical contact with each other due to the presence of the food container therebetween.

[0010] While it is possible for the first and second tools to be connected to separate frames, in most embodiments the second sealing tool is attached to the frame (i.e. the same frame) at a second attachment point such that the second sealing tool is supported by the frame. This configuration transfers all sealing forces generated by the system through the frame, improving precision and accuracy of measurements. This also simplifies manufacturing and installation of the system.

[0011] The frame may be any fixed support structure on which the first and / or second sealing tools are mounted. The frame typically does not include any movable elements, which are mounted within the frame. For example, the first and / or second sealing tools may be movable within the frame during the sealing operation. Similarly, a drive unit for driving the sealing tools may include movable elements, but is mounted on a fixed structure provided by the frame.

[0012] Preferably, the first sealing tool and / or the second sealing tool are removable from the frame without removing the strain gauge, which can conveniently be achieved by arranging the strain gauge to be attached to the frame, as described above.

[0013] In a particularly preferred embodiment, the frame comprises one or more frame elements forming at least a first closed loop, the first and second sealing tools are mounted such that when the first and second sealing tools are pressed together force is transmitted through the closed loop, and the strain gauge is mounted to the frame at a location along the closed loop. Although preferred, it is not necessary for the frame to transmit force through the closed loop, but instead force could be transmitted through, for example, a linear frame element extending between two mounting points of each sealing tool.

[0014] Preferably, the first closed loop defines a plane that is generally parallel to the direction of pressing the first and second sealing tools together. For example, the closed loop may surround the area in which the sealing tools are pressed together. The direction of pressing the first and second sealing tools may be generally in the plane that defines the closed loop, or may be offset. If offset, a second closed loop defined by a further frame element may be desired and offset in the opposite direction.

[0015] The first and second sealing tools are typically each mounted to one or more frame elements defining the first closed loop at different locations around the closed loop, preferably at locations generally opposite each other around the closed loop. It will be appreciated that this may include additional frame elements that are not part of the closed loop, connecting to the frame elements defining the closed loop. For example, as described below, one sealing tool may be mounted to a horizontal beam and connected at one end to a frame element defining the closed loop. Thus, any force transferred to the frame will be transferred to the horizontal beam and from there to the closed loop, as the frame resists the sealing force.

[0016] The advantage of a closed loop is that at least a first of the frame elements defining the first closed loop is removable from the other frame elements defining the first closed loop, and the strain gauge is attached to the first frame element. Removal of the first element will only open a section of the loop, so the frame will remain freestanding. This allows the strain gauge-equipped part to be removed and replaced without having to completely disassemble the frame or remove the sealing tool.

[0017] In general, the strain gauges are preferably attached to a part (or element) of the frame that extends either substantially parallel or perpendicular to the direction of pressing the first and second sealing tools together, and more preferably parallel. As a result, the forces passing through the frame are mainly tensile / compressive and shear forces, respectively. However, a part of the frame may or may not be an independent element of the frame. For example, if the frame includes elements that define a closed loop, the strain gauges may be attached to a first removable element, which preferably extends parallel to the direction of pressing the first and second sealing tools together. However, alternatively, the closed loop may be defined by a single continuous part, in which case the strain gauges may be attached to a part of that part that extends parallel to the direction configured to press the first and second sealing tools together.

[0018] However, it is preferred that the frame be configured so that the strain gauges are mounted in a portion of the frame that is substantially in pure tension when the first and second sealing tools are pressed together. As discussed above, this facilitates accurate measurement of the sealing force. However, this is not required and embodiments are described below that do not rely on measurements in the portion of the frame that is in pure tension.

[0019] In some embodiments, the frame comprises a support beam, the support beam is connected to the body of the frame (i.e. the rest of the frame, which may comprise one or more elements defining a closed loop) at first and second connection points along the length of the support beam, and the first sealing tool is attached to the support beam between the first and second connection points. For a number of reasons, this configuration is particularly preferred for measuring forces transmitted through the frame. As explained below, mounting a tool between the connections of a beam may cause large deflections of that beam during the sealing operation, making it particularly suitable for strain gauge measurements. Alternatively, the two connections to the rest of the frame are particularly suitable locations for placing strain gauges (e.g. as part of a load cell located between the body of the frame and the support beam at each connection point), without the need to place the strain gauge at the attachment point of the tool. If the strain gauge were located at the attachment point of the tool, the strain gauge may be damaged due to the possibility of changing the tool periodically.

[0020] As mentioned above, in a particularly preferred arrangement, at least one strain gauge is attached to the support beam between the first and second connection points. In particular, it is preferred that the strain gauge is located approximately equidistant between the first and second connection points and / or aligned with the first attachment point. If the first tool is connected to the support beam at multiple attachment points, the strain gauge may be located at one or each attachment point or between these attachment points. The optimal location for the strain gauge is usually the location where the most deflection occurs during sealing. Although it may be preferred to locate the strain gauge on the opposite side of the support beam to the first attachment point, the strain gauge may also be located on the same side of the support beam as the first attachment point. Alternatively or additionally, one or more strain gauges may be located on the side or each side of the support beam adjacent to the side on which the first attachment point is located. In some embodiments, multiple support beams may be provided, for example the first sealing tool may be attached to a pair of support beams, such as parallel support beams each having one or two attachment points. However, the use of a single support beam to which the first sealing tool is attached is advantageous as it typically results in a larger deflection for the same sealing pressure, allowing more accurate measurements by the strain gauges.

[0021] Preferably, the first and second sealing tools are configured to be pressed together along a direction generally perpendicular to the length of the support beam, typically with one, or possibly both, of the sealing tools moving along a direction generally perpendicular to the length of the support beam and pressed together along this direction, typically with this configuration allowing the support beam to deflect during the sealing process to provide accurate strain gauge readings.

[0022] Another advantage of the support beam is that it may be adjustably connected to the frame body at the first and second connection points so that the relative position of the first and second sealing tools can be adjusted. This may include adjustment to align the first and second sealing tools, for example by moving one tool laterally relative to the other tool or perpendicular to the direction of movement of one or both tools, but particularly preferably the adjustable connection allows adjustment of the distance between the first and second sealing tools, for example along the pressing or moving direction of one or both tools, to configure the pressure generated when the first and second sealing tools are pressed together. For example, one of the tools may have a predefined range of movement, and a small adjustment of the distance between the sealing tools may change the pressure generated when the tools are pressed together and this movable tool is at the extreme of its range of movement. The adjustable support beam allows adjustment of the pressure generated in the sealing process without adjusting the range of movement of the sealing tools. In particular, if the range of movement is controlled by an actuator, changing the range of movement of the actuator would result in increased or uneven wear of the actuator.

[0023] Preferably, the support beams are designed to be more compliant than the frame body. This may be accomplished by forming the support beams from a thinner or less dense material than the material forming the frame body. Alternatively, the beams themselves may have a smaller cross-sectional area than the other members of the frame body, or a smaller mass-to-length ratio than the other members of the frame body. Intentionally designing the support beams to be compliant allows for more accurate measurements with strain gauges, improving the measured seal pressure.

[0024] As previously mentioned, typically one of the first and second sealing tools is coupled to an actuator for moving the sealing tool to press the first and second sealing tools together. Preferably, the actuator is configured to linearly and reciprocally move the sealing tool from an open position capable of receiving a food container to be sealed, to a closed position in which the sealing tool is forced against the opposing sealing tool to seal the container.

[0025] Preferably, the first or second sealing tool coupled to the actuator is mounted to the frame via the actuator such that a force exerted by the actuator when pressing the first and second sealing tools together is transmitted to the frame, for example in the open position the sealing tool rests against the frame but may be lifted therefrom by the actuator and pressed against the opposing tool, and when the actuator presses the tools together a reaction force is transmitted to the frame through the actuator mounted to the frame.

[0026] Typically, the system further comprises a control device configured to control the actuator. Preferably, the control device is connected to at least one strain gauge and configured to control the actuator based on the measurement of the at least one strain gauge. In some cases, the control device may simply stop operation if a significant drop in sealing pressure is detected by the strain gauge. In other cases, the control device may be configured to control the actuator so that the peak measurement by the strain gauge reaches a predetermined value or falls within a predetermined range. That is, the control device may control the actuator to move the tool until a target peak pressure is reached, and then hold the sealing tool and / or return the sealing tool once the seal is made. The predetermined value or the predetermined range is determined by the specific tools installed in the system. Each tool has a weight per unit area appropriate for the type of seal and a target sealing force calculated from the sealing area of ​​the corresponding tool. The present invention always achieves this target sealing pressure without exceeding it, thus saving energy and providing an optimal and constant seal.

[0027] It may not be possible to control the actuator based on strain gauge measurements during a sealing movement to perform a particular sealing movement, since the stroke during sealing may be too fast to obtain an accurate reading and therefore the actuator cannot be controlled based on the reading. Instead, a calibration process may be performed to establish the amount of actuator movement required for a particular tool to reach a predetermined value or range measured by the strain gauge, and the actuator may then be controlled based on the measurement of at least one strain gauge during the calibration phase. In the calibration phase, the actuator may be moved slowly until a target sealing force is reached. The position of the actuator at this target sealing force may be stored by the system and used during subsequent sealing movements. Taking into account tolerances in tool manufacturing and also the variety of different tools installed, it may be seen that a calibration process needs to be performed each time a tool is changed. Furthermore, it may be desirable to perform a new calibration phase periodically to account for wear in the system.

[0028] In a particularly preferred embodiment, the actuator comprises a crank driven by the crankshaft to move the sealing tools, each sealing tool being configured such that the crank does not reach top dead center when the first and second sealing tools are pressed together. By adjusting the crank to reach a peak measured force before it reaches top dead center, the actuator can make corrections, for example increasing or decreasing the movement of the sealing tools as required to reach the desired sealing pressure. However, this is not essential and strain gauges may be used to set the relative mounting positions of the sealing tools such that the desired sealing force is achieved at the top dead center of the crank. This allows the crank to pass beyond top dead center and allows the crank to operate from different directions of the crankshaft, which promotes circulation of lubricant in the bearings. When using the system in a configuration in which the crank does not reach top dead center when the first and second sealing tools are pressed together, the method of operating the system may include changing the direction of the crankshaft that starts driving the crank during maintenance operations and / or replacement of sealing tools in use.

[0029] The present invention is particularly advantageous when the actuator comprises a motor. Motors are typically more cost-effective than pneumatic actuators, but do not provide accurate data regarding the force exerted by the motor. A typical motor drive configuration includes a motor and a crankshaft, with the sealing tool coupled to the crankshaft, and the rotational motion of the motor is converted into linear motion of the sealing tool, which presses against the opposing sealing tool. In some embodiments, the system is calibrated (e.g., by the adjustable support beam described above) to achieve the desired sealing pressure at the extreme end of the sealing tool's range of motion, which would correspond to the top dead center of the crank. This allows the sealing tool to be held in this position to perform the sealing operation while taking advantage of the alignment strength of the top dead center of the crank. However, as described above, in some embodiments of the present invention, the controller may use strain gauge measurements to control the movement of the sealing tool until the desired pressure is reached. In such cases, the desired sealing position is typically not coincident with the top dead center of the crank. This can increase wear on the actuator mechanism, as it is held at high pressure without the benefit of the alignment strength of the top dead center. Therefore, in some embodiments the motor is provided with a self-locking gearbox, for example with a self-locking worm gear, so that variations in the travel distance of the sealing tool do not increase wear on the actuator.

[0030] In systems with motors, the motor is preferably configured to measure motor torque. For example, the motor may be equipped with a torque sensor to measure the torque generated by the motor, or may be output directly from the motor controller. Motor torque alone is not sufficient to determine the sealing pressure, but in combination with strain gauge measurements, comparing the force transmitted through the frame to the torque generated by the motor can help diagnose problems with the system. More preferably, the system includes an encoder to measure actuator displacement. As with motor torque, actuator displacement alone is not sufficient to determine the sealing pressure, but again, in combination with strain gauge measurements, useful diagnostic insights can be obtained. For example, low sealing force and high motor torque may indicate a problem with the sealing tool, whereas low sealing force and low motor torque may indicate a problem with the motor. Also, high displacement for a given sealing force may indicate a problem with the silicone of the sealing tool.

[0031] Although both sealing tools may be driven by their own actuators or by the same actuator, preferably only one sealing tool is driven by an actuator. The other tool may be fixed or move passively when the drive tool is pressed. In particular, one of the first and second sealing tools is connected to an actuator and the other of the first and second sealing tools is substantially fixedly mounted relative to the frame, preferably substantially fixedly mounted to the frame. Although one tool is preferably substantially fixed relative to the frame, it may still include elements within the tool that move during sealing. However, it is preferred that any movement is passive, i.e. not driven by an actuator, but rather by one or more elements of the tool moving in response to the pressure of the opposing actuating tool, for example by a resilient connection such as a spring. However, even in these cases, the fixed sealing tool should be fixedly mounted to the frame or the like. Having only one of the sealing tools driven by an actuator significantly reduces the complexity of the system while still allowing accurate readings of the sealing force using strain gauges.

[0032] In the case where only one tool is movable by the actuator, it is preferably the first sealing tool that is fixed to the frame, i.e. the sealing tool that is attached to the support beam or the sealing tool in which the strain gauge is located at its attachment point to the frame.

[0033] Preferably, the first or second sealing tool comprises a tool body and one or more sealing parts movable relative to the tool body, the actuator being configured to bring the first sealing tool into contact with the second sealing tool during a first mobile phase, and to move the sealing parts relative to the tool body to press the sealing parts of the sealing tool against the other of the first and second sealing tools during a second mobile phase. For example, if the system is a tray or vacuum packing system, the movable tool may be a lower tool that holds a tray or support in the sealing parts. The actuator may be configured to lift the entire lower tool in the first phase to sandwich the sealing film between the two tools. When the lower sealing tool is pressed into the upper sealing tool, the elements may move relative to each other, such as by a spring, to seal the film to the container. In this way, a single actuator can be responsible for both the closing and sealing process of the tools, reducing the cost and complexity of the system. In this example, the strain gauge may take a first measurement at the end of the first mobile phase and a second measurement at the end of the second mobile phase. It may be necessary to take the difference between two or more measurements to distinguish between sealing forces and forces resulting from, for example, pinching a film between two tools.

[0034] Many embodiments further include a controller connected to the at least one strain gauge and configured to output an indication that the system is faulty based on the strain gauge readings, such as when the strain gauge peak readings are above or below a predetermined value when the first and second sealing tools are pressed together, preferably when the peak readings are outside a predetermined range. This is particularly preferred in systems where the actuator includes a motor and crankshaft configured to hold the tool forming the seal at top dead center. Lower than expected sealing pressures may result in improperly formed seals, and higher than expected sealing pressures may result in accelerated wear of various components of the system. The output indicating that the system is faulty may include one or more of an audible alarm, a warning on a screen, or a system shutdown.

[0035] If the system includes a torque sensor and / or an encoder, the controller is preferably connected to at least one strain gauge and further connected to the torque sensor and / or encoder, and the controller is configured to output an indication that the system is faulty based on a combination of the strain gauge readings and the encoder and / or torque sensor readings, and preferably the controller is configured to output an indication that the system is faulty based on a comparison of the strain gauge readings and the encoder and / or torque sensor readings over multiple sealing cycles. For example, in some systems the controller may control the motor to always reach the same sealing pressure. As the system wears over many cycles, the linear movement may gradually increase, so monitoring only the strain gauge readings may not identify a problem with the system. A large change in linear movement at the same sealing pressure may indicate a problem with the system, which the controller can identify by comparing these measurements over multiple consecutive sealing cycles. Alternatively, excessive peak torque at the same sealing pressure may highlight problems with tool lift and main bearings. The system may further identify when the movement during sealing requires the actuator to be moved to top dead center to achieve the desired sealing pressure, or within a predetermined distance, such as 1 mm, from top dead center using an encoder, indicating a problem with tool silicone, etc.

[0036] As mentioned above, a particular type of sealing system that benefits from the invention is one of the first and second sealing tools being an upper tool and the other of the first and second sealing tools being a lower tool, the lower tool being configured to receive and hold a container for sealing, the upper tool being configured to seal a lid, preferably a film-like lid, to the container. Preferably, the first sealing tool is the upper sealing tool and the second sealing tool is the lower, preferably driven, sealing tool. Preferably, in such a system, the upper tool comprises a heat sealing tool configured to heat seal the film-like lid to the container along a seam after sealing. More preferably, the upper tool comprises a cutting tool for cutting the container lid from the rolled material. Particularly preferably, the cutting tool is connected to the heat sealing tool via one or more elastic members, such that pressing the upper and lower tools together results in a relative movement between the cutting tool and the heat sealing tool. This allows the cutting and sealing steps to be performed separately, for example allowing the cutting tool to cut and seal the film without contacting a tray or support. Furthermore, since these two sealing stages involving relative movement are provided solely by the movement of the lower tool, no additional drive means for the upper tool are required.

[0037] According to a second aspect of the invention, a method of sealing a food container comprises the steps of providing a food container to be sealed between a first sealing tool and a second sealing tool, the first sealing tool being attached to a frame at at least a first attachment point such that the first sealing tool is supported by the frame, pressing the first and second sealing tools together to seal a food container located therebetween, and measuring the force transmitted through the frame when the first and second sealing tools are pressed together using at least one strain gauge attached to the frame. An alternative system envisages locating a strain gauge at the first attachment point between the frame and the first sealing tool.

[0038] This embodiment corresponds to a method of sealing a container using the system according to the first embodiment. All the preferred features explained above with respect to the first embodiment may be employed in this sealing method as well.

[0039] Particularly preferably, the method comprises the step of pressing the first and second sealing tools together based on measurements from at least one strain gauge, and even more preferably, pressing the first and second sealing tools together so that a peak measurement from the strain gauge exceeds a predetermined threshold or falls within a predetermined range.

[0040] The method may further comprise outputting an indication that the system is faulty if a peak measurement by the strain gauges when the first and second sealing tools are pressed together is above or below a predetermined value, preferably if the peak measurement falls outside a predetermined range.Alternatively or additionally, the method may comprise pressing the first and second sealing tools together using a motor having a torque sensor for measuring the torque produced by the motor, and outputting an indication that the system is faulty based on measurements of both the strain gauge and the torque sensor, preferably based on a comparison of the strain gauge and torque sensor measurements over a number of sealing cycles.

[0041] The invention will now be described with reference to the following drawings. [Brief description of the drawings]

[0042] [Figure 1] A perspective view of a system for sealing food containers [Figure 2A] FIG. 1 shows three front views of a system for sealing food containers, first with the tool in an open position and then showing two different stages during sealing. [Figure 2B] FIG. 1 shows three front views of a system for sealing food containers, first with the tool in an open position and then showing two different stages during sealing. [Figure 2C]FIG. 1 shows three front views of a system for sealing food containers, first with the tool in an open position and then showing two different stages during sealing. [Diagram 3] FIG. 1 is a side view of a system for sealing food containers, with various parts omitted for clarity; [Figure 4] FIG. 1 shows a component of a system for sealing food containers, illustrating how this element deforms during sealing. [Diagram 5] 1 is a flow chart illustrating a method of operating a system for sealing food containers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] An example of a system will now be described with reference to Figures 1 to 4. The system shown in Figure 1 is a tray sealing system 1. The system comprises a frame 100 with various frame elements, which will be described in more detail below, and a number of housing panels 110 which close the frame to form housings for the various elements of the system. The system comprises a film supply unit 10 having a film supply reel 11 which supplies film from a web into the system along a film transport path 13, and a take-up reel 12 which receives excess film. The system further comprises a sealing unit 20 which lifts food trays, seals the film to the trays and cuts the film from the web. As will be described below, the sealing unit 20 comprises an upper tool 21 and a lower tool 22 which are pressed together as part of the sealing process by an actuator 25 which is connected to the lower sealing tool 22. The system further comprises a controller 30 with a user interface for controlling the operation of the system, and a transport system 40 for transporting trays through the system. The transport system 40 comprises a first transport belt 41 which receives the trays to be sealed at the input end of the system and transports the trays to the sealing unit 20. From there the trays are transferred into the sealing unit, for example by a gripper arm. In the unit the trays are sealed and transported out of the sealing unit after sealing. A second transport belt 42 receives the sealed trays and transports each tray to the output end of the system.

[0044] The sealing unit 20 is located in the central part of the system 1. It comprises an upper sealing tool 21, which is substantially fixedly mounted on the frame 100, although it typically comprises moving parts within the upper tool. This sealing unit is configured to perform tray sealing or vacuum packing. To this end, the upper sealing tool 21 typically comprises a heat sealing plate for heat sealing the film to the edge of the support, such as a tray, and a cutting tool for cutting off an area of ​​the film that has been welded to the support, such as a tray. The lower sealing tool 22 typically comprises a receiver configured to receive the support, such as a tray, to be sealed. An actuator may lift the lower sealing tool and press the lower sealing tool 22 against the upper sealing tool 21 so that sealing is performed. When the upper and lower sealing tools are closed, the actuator may further lift the lower sealing tool, which may cause relative movement of parts within one or both of the upper and lower sealing tools. For example, the upper tool includes a heat-sealing plate and a cutting tool that are spring-mounted to the body or housing of the upper sealing tool, and the body or housing of the upper sealing tool moves upward when pressed by the lower tool, causing the heat-sealing plate and the cutting tool to protrude from the body or housing of the upper sealing tool and contact the tray. Such a configuration of the heat-sealing plate and the cutting tool in the upper sealing tool is described in co-pending application PCT / GB2021 / 052230.

[0045] 2A-2C show the sealing process. The lower sealing tool is connected to and supported by an actuator 25. The lower sealing tool 22 is constrained to and slides relative to elements of the frame so that the actuator can only move the lower sealing tool vertically. The actuator 25 includes a motor 26 which rotates a crankshaft to reciprocate a crank arm 27. The motor preferably includes a torque sensor for measuring motor torque and an encoder for measuring actuator displacement by the motor. The distal end of the crank arm 27 is coupled to the lower sealing tool 22 such that movement of the crank arm 27 lifts the lower sealing tool 22. As will be described below, the actuator 25 is connected to the frame 100 so that the sealing force is transferred through the frame when the sealing tools are pressed together. Meanwhile, the upper sealing tool 21 is substantially fixedly attached to a horizontal support beam 103 of the frame 100 at attachment points 21a and 21b as will be described below.

[0046] FIG. 2A shows the tools in an open position. In this view, the crank arm 27 has been lowered and the lower tool 22 is away from the upper tool 21 so that the trays can be conveyed into the sealing unit 20 and received by the lower sealing tool 22. FIG. 2B shows the sealing unit 20 after the lower sealing tool 22 has been lifted by the actuator to contact the upper sealing tool. The lower sealing tool 22 is lifted by the motor 26 rotating the crankshaft, displacing the crank arm 27 towards the upper sealing tool 21. With the sealing tools in this position, a film (not shown in FIG. 2B) is sandwiched between the upper sealing tool 21 and the lower sealing tool 22, but no sealing process is taking place. FIG. 2C shows the sealing tools after the actuator has further lifted the lower sealing tool 22. As described above, this presses the outer body of the upper sealing tool 21 upwards, causing the heat welding plate and cutting tool in the upper sealing tool to move relative to the outer body of the upper sealing tool 21, and the cutting and sealing process is carried out. The heat seal plate of the upper sealing tool 21 may be fixedly attached to the frame and, in the position shown in Figure 2C, the tray may be pressed against this heat seal plate to generate the required sealing pressure.

[0047] As shown in FIG. 2C, the system may be configured such that the required sealing pressure is generated when the crank arm 27 reaches the top dead center position. This configuration has the advantage that the system benefits from the alignment strength at the top dead center position while holding the tray in the sealing position. To configure the system to achieve the required sealing pressure at the top dead center position, the vertical position of the upper sealing tool 21 is adjusted. In this embodiment, this adjustment is achieved by attaching the horizontal beam 103 to the support part of the frame 100 at connection points 103a, 103b at both ends of the horizontal beam 103 via jack screws, allowing fine adjustment of the vertical position of the horizontal beam. This adjustment process may be performed based on the readings of the strain gauges 121 or 122, which will be further described below.

[0048] Alternatively to the configuration shown in FIG. 2C, the system may be configured to reach the desired sealing pressure before the crank arm 27 reaches top dead center, i.e., each sealing tool is in the position shown in FIG. 2C. The system may be configured in this way by lowering the beam 103 on the screw jack. In this alternative configuration, the crank arm 27 may be raised based on the readings of the strain gauges 121, 122 until the desired sealing pressure is reached. The advantage of this configuration is that the sealing pressure can be adjusted as required, and the actuator can further compensate for changes in tolerances in the system. When the system is used in this way, it is preferable that the motor 26 is equipped with a self-locking gearbox.

[0049] The frame 100 comprises a number of frame elements which surround and support the sealing unit 20. Immediately upstream of the sealing unit 20 are first and second frame elements 101, 102 which form a closed loop. In particular, the second frame element is a single metal plate which forms a horizontal base part 102a of the frame. This base part extends across the entire width of the system below the sealing tools 21, 22. At the rear of the system, i.e. on the right hand side of FIG. 4, a vertical frame part 102b extends upwards from the base part 102a. This vertical frame part 102b is an arm part which extends between the base part 102a and an upper frame part 102c. The upper frame part 102c is located near the upper sealing tool and extends across the width of the system. At the front of the system, i.e. on the left hand side of FIG. 4, a vertical frame part 102d extends downwards from the upper frame part 102c. The vertical frame section 102d is an arm extending from the upper frame section 102c partway towards the lower frame section 102a. The first frame element 101 is another straight metal plate with its upper end connected to the lower end of the vertical frame section 102d and its lower end connected to the lower frame section 102a. The first frame element may be connected to the second frame element 102, for example, by bolts. This connection may be made using 16mm steel dowels, providing accurate positioning and full shear strength of the joint. This arrangement of the first and second frame elements forms a closed loop lying in a vertical plane. Each tray can pass through the center of this loop and through the frame along the transport system 40. The plane of this closed loop is approximately parallel to the direction in which the first and second sealing tools are pressed together.

[0050] As will be explained in more detail below, the upper sealing tool 21 is supported by the upper frame part 102c and the lower sealing tool 22 is supported by the lower frame part 102a so that when the sealing tools are pressed together the frames resist the sealing force and the vertical frame parts 102b, 102d and the first frame element 101 are in tension. The first frame element 101 is provided with a strain gauge 122 which measures the tension in the first frame element. This strain gauge may be, for example, a two-hole bolt-on strain gauge sensor manufactured by Datum Electronics Ltd, Datum Global HQ, Castle Street East Cowes, Isle of Wight PO32 6EZ. Providing the strain gauge on the removable first frame element 101 allows the gauge to be easily removed from the wider frame for repair or replacement. Furthermore, by locating the strain gauge parallel to the direction of pressing the sealing tools together and on an element that is in net tension the sealing force can be more easily known.

[0051] Although each frame element defining a single closed loop may support a tool, in this embodiment an additional frame element 104 is provided defining a second closed loop, parallel to the first and second frame elements and immediately downstream of the sealing unit 20 along the conveying direction. In this embodiment the second closed loop 104 is formed by a single element, but it could also be formed by two frame elements like the first closed loop, which allows for another strain gauge to be provided on a removable frame element in the second closed loop.

[0052] As mentioned above, the frame further comprises a horizontal beam 103 extending between these two closed loops above the upper sealing tool 21. On the downstream face of the second frame element 102 and on the beam 103 there is a connection point 103a in the form of a bracket with two vertical screw holes. The beam 103 is connected at its upstream end to the second frame element by a screw jack that passes through the screw holes of the bracket and is received in the beam 103. A similar connection point 103b is also provided on the upstream face of the further frame element 104, where the downstream end of the beam 103 is connected to the frame element that defines the second closed loop. As mentioned above, the upper sealing tool 21 connects to the underside of the beam 103 at first and second attachment points 21a, 21b. These points may comprise bolts that pass through openings in the beam 103 and are received in the mounting posts of the upper sealing tool 21. Another strain gauge may be provided on the beam 103 between these two attachment points 21a, 21b. The strain gauge may be of the same type as described above, or may be a more sensitive strain gauge for detecting smaller changes in elongation. Alternatively or additionally, a strain gauge may be located between the beam 103 and the upper sealing tool at one or both of the attachment points 21 a, 21 b.

[0053] The frame 100 further comprises a lower tool mounting element 105, which extends between the two closed loops below the lower sealing tool 11. In particular, the frame element 105 connects to the lower frame part 102a of the second frame element 102 via connection 105a and to the lower part of the further frame element 104 via connection 105b. As mentioned above, the lower sealing tool 22 is coupled to a crank arm 27, which connects via a crankshaft to the motor 26 of the actuator 25. The actuator 25 connects to the frame mounting element 105 via connection point 25a.

[0054] By configuring the sealing tools 21, 22 on the frame in this way, when they are pressed together, a sealing force is transmitted to the two closed loops of the frame. In particular, when the upper sealing tool is pressed upwards, it is reacted to by a beam 103, the ends of which are connected to the frame element 102 on the upstream side and to a further frame element 104 on the downstream side. Similarly, when the actuator presses the lower sealing tool upwards, a reaction force is transmitted to the frame element 105 and then to the frame element 102 on the upstream side and to the further frame element 104 on the downstream side. Thus, the sealing force is transmitted through the two closed loops of the frame.

[0055] In principle, any of the frame elements 101, 102, 103, 104 and 105 may be provided with a strain gauge. However, it is preferable to provide a strain gauge in each area where significant deflection or tension occurs during sealing. As mentioned above, the first frame element 101 is part of one of the arms connecting the upper and lower frame parts which are part of the closed loop through which the sealing force is transmitted. This element is subject to net tension during sealing and is therefore a good place to provide a strain gauge. On the other hand, the beam 103 is perpendicular to the direction of pressing the sealing tools together and is directly above the upper sealing tool 21, so it will experience significant deflection during the sealing process. This deflection may be increased by making the beam 103 from a thinner and / or more flexible metal than the other frame elements resisting the sealing force. For example, the beam 103 may be made of stainless steel 304 and have a thickness of 5 mm, while each of the other frame elements is made of stainless steel 304 and has a thickness of 10 mm.

[0056] 4 shows the deflection of the beam 103. As can be seen, the area of ​​maximum deflection is between the first attachment point 21a and the second attachment point 21b. Therefore, this location may be a preferred location for one of the strain gauges in the system.

[0057] Regardless of where the strain gauge is located on the frame, it will need to be calibrated before use with a particular tool that will be installed in the system during normal use. This calibration involves installing the tool that is intended for use in the system and placing a load cell on the tool. An actuator may then be used to press the tools together with the load cell between them, in the range of forces that the load cell will detect. As the tools are pressed together, the output from the strain gauge is recorded and the strain gauge output is plotted against the force measured by the load cell. From there, a relationship can be determined between the strain gauge readings and the sealing force (usually in mV·kN -1 ) relationship can be derived. Finally, the load cell is removed and one or more trays are placed in the tool and sealed. The tools may be slowly pressed together until the desired sealing force is reached. The sealing force is determined by strain gauge measurements combined with the relationship derived using the load cell. As mentioned before, the required sealing force will vary from tool to tool depending on the type of seal being produced, the number of trays being sealed at one time, and the total sealing area of ​​each tray. Once the required sealing pressure is reached for a particular tool, the actuator position is stored for future seal movements.

[0058] A method of operating one of the disclosed systems will now be described with reference to FIG.

[0059] Beginning at step S100, food containers to be sealed are provided between the custom modified part tools of the upper sealing tool 21 and the lower sealing tool 22. At this stage, the system is configured as shown in FIG. 2A with the sealing tools in an open position. The system may be configured to seal multiple containers at once, and so a designated number of trays may be moved between the sealing tools. As previously described, these food containers are provided to the sealing unit 20 by the first conveyor 41 and may be transferred into the sealing unit 20 by a gripper arm or the like.

[0060] In a second step S200, the actuator 25 is used to raise the lower sealing tool 22 into contact with the upper sealing tool 21. This causes the film and the container to be sealed to be sandwiched between the two sealing tools 21, 22. This corresponds to the position of Figure 2B.

[0061] From this point, the system may monitor the strain gauge 121, 122 readings in step S300 to determine the force transmitted through the frame. Although this step is shown to occur before the subsequent step S400, it should be understood that the strain gauge 121, 122 measurements preferably continue throughout the sealing process. Note that if the actuator 25 includes a motor 26 having a torque sensor and encoder, the method may include monitoring the strain gauge readings, the encoder position, and the torque sensor readings. Typically these items will correlate between the calibration cycle and the sealing cycle, but if one deviates relative to the other it may be an indication of a system fault. This may be used to output an indication that the system requires maintenance or is defective, and shut down the system.

[0062] In step S400, the actuator 25 presses the lower sealing tool against the upper sealing tool to seal the food container. This may include forcing the tools together until a desired sealing pressure is reached as determined by strain gauge 121, 122 measurements. Alternatively, for faster systems, the tools may be pressed together based on the proper actuator position determined during calibration and strain gauge measurements used to verify the sealing process and monitor for signs of error. In another alternative, the system may be calibrated and configured to reach the desired sealing pressure at the top dead center of the crank arm 27. This is shown in FIG. 2C. In this latter case, the strain gauges 121, 122 may be used to verify that the desired sealing pressure is achieved at the top dead center, and an indication may be output indicating that the system is faulty if this pressure is not achieved or exceeded as measured by the strain gauges 121, 122.

[0063] In step S500, the sealing tools are opened using actuator 25. If the desired sealing pressure is reached at top dead center, the crank arm may be moved to the opposite side of the crankshaft from the start to even out bearing wear.

[0064] Finally, in step S600, the sealed container (or containers) is removed from the lower sealing tool. A gripper arm may be used to transfer the sealed container to the conveyor belt 42. The process then returns to step S100 to seal additional food containers.

Claims

1. 1. A system for sealing food containers, comprising: A frame, a first sealing tool attached to the frame at at least a first attachment point for support by the frame; a second sealing tool configured to be pressed together to seal a food container located between the first and second sealing tools; and at least one strain gauge attached to the frame configured to measure a force transmitted through the frame when the first and second sealing tools are pressed together.

2. The system of claim 1 , wherein the second sealing tool is attached to the frame at a second attachment point so as to be supported by the frame.

3. 3. The system of claim 2, wherein the frame comprises one or more frame elements forming at least a first closed loop, the first and second sealing tools are mounted such that when the first and second sealing tools are pressed together a force is transmitted through the closed loop, and the strain gauge is mounted to the frame at a position along the closed loop.

4. The system of claim 3 , wherein the first closed loop defines a plane generally parallel to a direction in which the first and second sealing tools are pressed together.

5. 5. The system of claim 3 or 4, wherein the first and second sealing tools are each attached to the one or more frame elements defining the first closed loop at different positions around the closed loop, preferably at positions generally opposite each other around the closed loop.

6. 6. The system of claim 3, wherein at least a first of the frame elements defining the first closed loop is detachable from the other frame elements defining the first closed loop, and the strain gauge is attached to the first frame element.

7. 2. A system according to any preceding claim, wherein the strain gauge is mounted on a portion of the frame that extends generally parallel to a direction in which the first and second sealing tools are pressed together.

8. 2. A system according to any preceding claim, wherein the strain gauge is mounted to a portion of the frame which is subjected to substantially pure tension when the first and second sealing tools are pressed together.

9. 10. The system of any preceding claim, wherein the frame comprises a support beam connected to a body of the frame at first and second connection points along a length of the support beam, and the first sealing tool is attached to the support beam between the first and second connection points.

10. 10. The system of claim 9 when dependent on at least claim 3, wherein one end of the support beam connects to the one or more frame elements defining the first closed loop.

11. 11. The system of claim 9 or 10, wherein the at least one strain gauge is attached to the support beam between the first connection point and the second connection point.

12. 12. The system of claim 9, wherein the first and second sealing tools are configured to be pressed together along a direction generally perpendicular to a length of the support beam.

13. A system as described in any one of claims 9 to 12, wherein the support beam is adjustably connected to the frame body at the first and second connection points so that the relative positions of the first and second sealing tools can be adjusted, preferably so that the distance between the first and second sealing tools can be adjusted to configure the pressure generated when the first and second sealing tools are pressed together.

14. 14. The system of claim 9, wherein the support beams are formed from a material that is thinner or less dense than a material that forms the frame body.

15. 2. A system according to any preceding claim, wherein one of the first and second sealing tools is coupled to an actuator for moving the one of the sealing tools to press the first and second sealing tools together.

16. The system of claim 15 , wherein the other of the first and second sealing tools is substantially fixedly mounted to the frame.

17. 17. The system of claim 15 or claim 16, wherein the first or second sealing tool coupled to the actuator is attached to the frame via the actuator so that the force exerted by the actuator when pressing the first and second sealing tools together is transmitted to the frame.

18. 18. A system as described in any one of claims 15 to 17, further comprising a control device configured to control the actuator, the control device being connected to the at least one strain gauge and configured to control the actuator based on measurements of the at least one strain gauge, preferably the control device being configured to control the actuator such that peak measurements by the strain gauge fall within a predetermined range or exceed a predetermined target.

19. 20. The system of claim 18, wherein the actuator comprises a crank driven by a crankshaft to move the sealing tools, each sealing tool configured such that the crank does not reach top dead center when the first and second sealing tools are pressed together.

20. 20. The system of claim 15, wherein the actuator comprises a motor.

21. 21. The system of claim 20, wherein the motor comprises a self-locking gearbox.

22. 22. The system of claim 20 or 21, wherein the motor is configured to measure motor torque.

23. 23. The system of claim 15, further comprising an encoder for measuring the displacement of the actuator.

24. 24. The system of claim 15, wherein the first or second sealing tool comprises a tool body portion and one or more sealing portions movable relative to the tool body portion, and wherein in a first movement phase, the actuator is configured to bring the first sealing tool into contact with the second sealing tool, and in a second movement phase, the actuator is configured to move the sealing portions relative to the tool body portion to press the sealing portions of the sealing tool against the other of the first and second sealing tools.

25. A system as described in any preceding claim, further comprising a control device connected to the at least one strain gauge and configured to output an indication that there is a fault in the system if a peak measurement value by the strain gauge when the first and second sealing tools are pressed together is above or below a predetermined value, preferably if the peak measurement value falls outside a predetermined range.

26. 24. The system of at least claim 22 and / or 23, further comprising a control device connected to at least one strain gauge and further connected to the encoder and / or the torque sensor, the control device configured to output an indication that there is a defect in the system based on the strain gauge measurements and the encoder and / or the torque sensor measurements, preferably the control device configured to output an indication that there is a defect in the system based on a comparison using the strain gauge measurements and the encoder and / or the torque sensor measurements over a number of sealing cycles.

27. 10. A system as claimed in any preceding claim, wherein one of the first and second sealing tools is an upper tool and the other of the first and second sealing tools is a lower tool, the lower tool configured to receive and hold a container for sealing and the upper tool configured to seal a lid, preferably a film lid, to the container.

28. 30. The system of claim 27, wherein the top tool comprises a heat welding tool configured to heat seal a film lid to the container along a sealed seam.

29. 29. The system of claim 28, wherein the upper tool comprises a cutting tool for cutting the container lid from the rolled material, preferably the cutting tool is connected to the heat welding tool via one or more elastic members, and wherein pressing the upper and lower tools together creates relative movement between the cutting tool and the heat welding tool.

30. 10. The system according to any of the preceding claims, wherein the system is a tray sealing system or a vacuum packing system.

31. 1. A method of sealing a food container, comprising: providing a food container to be sealed between a first sealing tool and a second sealing tool, the first sealing tool being attached to a frame at least at a first attachment point such that the first sealing tool is supported by the frame; pressing the first and second sealing tools together to seal the food container therebetween; and measuring the force transmitted through the frame when the first and second sealing tools are pressed together with at least one strain gauge attached to the frame.

32. 32. A method according to claim 31, carried out using a system according to any one of claims 1 to 30.

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