Patent Application
20250187771
The invention relates to systems and methods for sealing food containers, in particular food containers such as trays of food or skin sealed trays or sheets. The invention is concerned with the measuring of seal pressure generated by such systems and methods, in particular so that sealing forces can be automatically configured for individual tooling, ensuring optimum seal and energy efficiency.
Many systems and methods of sealing food containers use a high pressure generated between two sealing tools to seal a container. A particular example of such a system is a tray sealing system, which generally seals a film lid to a tray using heat and pressure to seal the film along a sealed seam about the periphery of the tray. Another example of such a system is a skin seal system, which forms a sealed container by evacuating the air between a tray or sheet and a film cover, before sealing the film over the food product, again along a sealed seem generated using heat and pressure.
In these processes that form seals using heat and pressure, three major factors affect the quality of the seal formed: the time that the heat and pressure are exerted over, the temperature used in the sealing process, and the pressure being used to form the seals. Time and temperature are the most straightforward to measure and control; however, ensuring that the sealing pressure is high enough to form an adequate seal is much more difficult. Some sealing systems press the sealing tools together using actuators, such as pneumatic actuators, which can directly measure the force they are exerting and so provide a means of determining the sealing pressure. However, such actuators are generally more complex and expensive to buy and maintain than their alternatives.
It is therefore desirable to provide a system and method of sealing food containers that is not dependent on the actuator pressing the tools together to be able to monitor the seal pressure generated during the process of sealing a food container.
In accordance with 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 least at a first mounting point so as to be supported by the frame; a second sealing tool, the first and second sealing tools being configured to be pressed together in order to seal a food container positioned therebetween; at least one strain gauge configured to measure the force transmitted through the frame as the first and second sealing tools are pressed together, the at least one strain gauge being attached to the frame. In alternative systems, it is envisaged that the strain gauge may be positioned between the frame and the first sealing tool at the first mounting point.
The present system uses at least one sealing tool that is mounted to and supported in use by a frame and utilises the fact that the force acting on the tool that is supported by the frame will be transmitted into the frame. The system uses a strain gauge attached either directly to the frame or at the first mounting point. Where the strain gauge is attached directly to the frame, the strain gauge may measure the compression, deflection or tension of the frame as the seal is formed in order to measure the sealing pressure, i.e. by being arranged in a position of the frame that is in compression or tension or is deflected as the sealing tools are pressed together. Arranging the strain gauge so as to be in a position of the frame that is in tension or is deflected as the sealing tools are pressed together, is particularly preferred, since these may be more common in a supporting frame and may provide a more accurate reading of the sealing pressure. For example, the strain gauge may be adhered directly to a surface of the frame. Embodiments in which the strain gauge is attached directly to a surface of the frame are particularly preferred, being the most cost-effective solution. Alternatively, where the strain gauge is located at the first mounting point, this may be as part of a load cell positioned between the first sealing tool and the frame in order to measure the sealing pressure.
While alternative systems are foreseen in which the strain gauge is be between the frame and the first sealing tool at the first mounting point, providing that the at least one strain gauge is attached to the frame, particularly a part of the frame that is in deflection or tension as the sealing tools are pressed together, is particularly advantageous. This is because the first mounting point, at which the first sealing tool is connected to the frame, is routinely interacted with, such as when the sealing tool is being removed or replaced, and so the strain gauge would be liable to damage or require removing or replacing along with the sealing tool.
As noted above, one strain gauge, appropriately positioned, may be sufficient to measure the sealing pressure of the system; however, a plurality of strain gauges may be preferred in some circumstances. For example, if the first sealing tool is mounted to the frame at a plurality of mounting points, it may be preferred to provide a strain gauge between the frame and the first sealing tool at each mounting point. Alternatively, if the frame comprises a pair of beams or pillars that deflect as the seal is formed, then it may be preferred to couple a strain gauge at each such location to provide a more accurate measurement.
It will be appreciated that when the first and second tools are pressed together, they may not physically contact one another because of the food container located therebetween.
While it is possible that the first and second tools could be connected to separate frames, in the majority of embodiments, the second sealing tool is mounted to the frame, i.e. the same frame, at a second mounting point so as to be supported by the frame. This arrangement may ensure that all sealing force generated by the system is transmitted through the frame and so improve measurement accuracy and precision. This also makes the system easier to manufacture and install.
The frame may be any fixed support structure to which the first and/or second sealing tools are mounted. The frame will generally not comprise any movable elements, these mounted within the frame. For example, the first and/or second sealing tools may be movable within the frame during sealing. Similarly, a drive unit for driving the sealing tool may comprise movable elements but will be mounted to the fixed structure provided by the frame.
Preferably, the first sealing tool and/or the second sealing tool are removable from the frame without removal of the strain gauge. As indicated above, this may be conveniently achieved by arranging the strain gauge so as to be attached to the frame.
In particularly preferred embodiments, the frame comprises one or more frame elements defining at least a first closed loop, wherein the first and second sealing tools are mounted such that a force is transmitted through the closed loop as the first and second sealing tools are pressed together, and wherein the strain gauge is attached to the frame at a position along the closed loop. While preferred, the frame does not need to transmit the force through a closed loop, and could instead, for example, transmit the force through one linear frame element extending between the two mounting points for the respective sealing tools.
Preferably, the first closed loop defines a plane that is substantially parallel to the direction along which the first and second sealing tools are pressed together. For example, the closed loop may surround the region in which the sealing tools are pressed together. The direction along which the first and second sealing tools are pressed together may lie substantially in the plane defines by the closed loop, of could be offset. In the case of an offset, a second closed loop defined by further frame elements may be desired, which may be offset in an opposite direction.
The first and second sealing tools are each typically mounted to the one or more frame elements defining the first closed loop at different positions around the closed loop, preferably substantially opposite to one another around the closed loop. It will be appreciated that this may involve further frame elements that are not part of the closed loop connecting to the frame elements defining the closed loop. For example, as will be described below, one sealing tool may be mounted to a horizontal beam, which may be connected at one end to frame elements defining the closed loop. Thus, any force transmitted to the frame will be transmitted into the horizontal beam and from there into the closed loop, as the frame resists the sealing force.
An advantage of a closed loop is that at least a first of the frame elements that define the first closed loop may be detachable from the other frame elements defining the first closed loop, wherein the strain gauge is attached to said first frame element. The frame may still be self-supporting when the first element is removed, since this would merely open one section of the loop. This would allow the section carrying the strain gauge to be removed and replaced without full disassembly of the frame and without removing any of the sealing tools.
In general, it will be preferred for the strain gauge to be attached to a part (or element) of the frame that extends either substantially parallel or perpendicular to the direction along which the first and second sealing tools are configured to be pressed together, with parallel being particularly preferred. This would result in the force through the frame being predominantly a tension/compression force or a shear force respectively. It should be noted that the part of the frame may or may not be an independent element of the frame. For example, if the frame comprises the elements defining a closed loop, then the strain gauge may be attached to the first detachable element, which will preferably extend parallel to the direction along which the first and second sealing tools are configured to be pressed together. However, alternatively, the closed loop may be defined by a single continuous piece, in which case the strain gauge may be attached to a part of that piece that extends parallel to the direction along which the first and second sealing tools are configured to be pressed together.
However, the frame is configured, preferably the strain gauge is attached to a part of the frame substantially in pure tension as the first and second sealing tools are pressed together. As alluded to above, this facilitates an accurate measurement of the sealing forces. This is not essential, however, and embodiments will now be described that do not rely on measurement of parts of the frame in pure tension.
In some embodiments, the frame comprises a support beam, the support beam being connected to a body of the frame (i.e. the rest of the frame, which may include the one or more elements defining the closed loop) at first and second connection points along the length of the support beam, wherein the first sealing tool is mounted to the support beam between the first and second connection points. This arrangement is particularly preferred for measuring the force transmitted through the frame for a number of reasons. As will be explained below, a single beam to which one tool is mounted between its connection points may cause a significant flex in that beam during sealing, which is particularly suited to a strain gauge measurement. Alternatively, the two connection points to the rest of the frame may be a particularly suitable location to position strain gauges, e.g.
as part of load cells positioned between the body of the frame and the support beam at each connection point, which therefore means that the strain gauge does not need to be at the mounting point of the tool, which may be regularly subject to tool changes that could damage any strain gauge located at the mounting point.
As mentioned above, a particularly preferred configuration is one in which the at least one strain gauge is attached to the support beam between the first and second connection points. In particular, preferably the strain gauge is located approximately equidistant between the first and second connection points and/or aligned with the first mounting point. If the first tool is connected to the support beam at more than one mounting point, a strain gauge may be positioned at one or each mounting point, or between the mounting points. The optimum position for a strain gauge will typically be the or each position that experiences the most deflection during sealing. It may be preferred to position the strain gauge on the opposite side of the support beam to the first mounting point, but the strain gauge could also be positioned on the same side of the support beam as the first mounting point. Alternatively, or additionally, one or more strain gauges may be positioned on the or each side of the support beam that is adjacent to the side in which the first mounting point is located. In some embodiments, more than one support beam may be provided, e.g. the first sealing tool may be mounted to a pair of support beams, such as parallel support beams, each having one or two mounting points. However, the use of a single support beam to which the first sealing tool is mounted, is advantageous, as this will typically provide a greater degree of deflection for the same sealing pressure, which can then provide a more precise measurement by the strain gauge.
Preferably, the first and second sealing tools are configured to be pressed together along a direction substantially perpendicular to the length of the support beam. Typically, this will involve preferably one, or possibly both, of the sealing tools moving along a direction substantially perpendicular to the length of the support beam so as to be pressed against one another along this direction. This arrangement will typically cause the support beam to deflect during the sealing process, allowing for a good reading to be made with the strain gauge.
Another advantage of a support beam may involve the support beam being adjustably connected to the body of the frame at the first and second connection points so as to enable adjustment of the relative position of the first and second sealing tools. While this could include adjustment to line up the first and second sealing tools, e.g. by moving one tool laterally relative to the other or perpendicular to the direction along which one or both of the tools is moved, in particular it is preferred that the adjustable connections enable adjustment of the distance between the first and second sealing tools, e.g. in the direction along the pressing direction or direction of movement of one or both tools, for configuring the pressure generated when the first and second sealing tools are pressed together. For example, one of the tools may have a predefined movable range and so a small adjustment of the distance between the sealing tools may change the pressure generated when the tools are pressed together and said movable tool is at the extreme of its moveable range. An adjustable support beam enables adjustment of the pressure generated in the sealing process without having to adjust the movable range of the sealing tools. In particular where the movable range is controlled by an actuator, changing the movable range of the actuator can cause increased or uneven wear on the actuator.
Preferably, the support beam is designed to be more compliant than the body of the frame. This may be achieved by providing that the support beam is formed of a material that is thinner or less dense than the material used to form the body of the frame. Alternatively, the beam itself may have a smaller cross-section than other members of the body of the frame, or have a smaller mass to length ratio than the than other members of the body of the frame. By deliberately designing the support beam to be compliant, this enables more precise measurements to be made by the strain gauge and so improves the seal pressure measurements.
As mentioned above typically, one of the first and second sealing tools is coupled to an actuator for moving said sealing tool in order to bring the first and second sealing tools together so as to be pressed together. Preferably, the actuator is configured to move the sealing tool in a linear and reciprocal manner from an open position, at which a food container to be sealed may be received, to a closed position, and which the sealing tool is pressed against the opposing sealing tool in order to seal the container.
Preferably the first or second sealing tool that is coupled to the actuator is mounted to the frame via the actuator, such that the force exerted by the actuator when the first and second sealing tools are pressed together is transmitted to the frame. For example, in an open position, the sealing tool may rest on the frame, but may be lifted from there by the actuator and pressed into the opposing tool such that as the actuator presses the tools together, the reaction force is transmitted to the frame through the mounting of the actuator to the frame.
Typically the system will further comprise a controller configured to control the actuator. Preferably, the controller is connected to the at least one strain gauge and is configured to control the actuator based on measurements of the at least one strain gauge. In some cases, this may simply involve the controller ceasing to operate if the strain gauge finds a significant drop in seal pressure. In other cases, this may involve the controller being configured to control the actuator such that a peak measurement by the strain gauge reaches a predetermined value or falls within a predetermined range. That is, the controller may control the actuator to move the tool until a target peak pressure is reached, before holding and/or returning the sealing tool once a seal is made. The predetermined value or predetermined range will be determined by the particular tool installed in the system. Each tool will have a target seal force that is calculated from optimum weight per unit area for the seal type and the sealing area for the tool in question. The present invention ensures that this target sealing pressure is achieved consistently without being exceeded and so saves energy and achieves optimal consistent sealing.
It should be noted that it may not be possible to control the actuator to perform a given sealing stroke based on the strain gauge measurements during that sealing stroke, as a sealing stroke may be too fast to get an accurate reading and control the actuator based on that reading. Instead, a calibration process may be performed to establish the amount of actuator movement required to reach the predetermined value or predetermined range as measured on the strain gauge for a particular tool, and then the actuator may be controlled based on the measurements of the at least one strain gauge during the calibration phase. In the calibration phase, the actuator may be moved slowly until the target sealing force is reached. The actuator position at this target sealing force may be stored by the system and then used in future sealing stroked. It will be appreciated that the calibration process will need to be performed each time the tool is changed to account for tolerances in the manufacture of the tools, or even to account for different tool types being installed. It may also be desirable to run a new calibration phase periodically to account for wear in the system.
In particularly preferred examples, the actuator comprises a crank driven by a crankshaft for moving the sealing tool, wherein the sealing tools are configured such that the crank does not reach top dead centre when the first and second sealing tools are pressed together. By arranging that the peak measurement force is reached before the crank reaches top dead centre, this allows the actuator to compensate, e.g. move the sealing tool more or less as required to reach the desired sealing pressure. This is not essential, however, and the strain gauge may be used to configure the relative mounting positions of the sealing tools so that the desired sealing force is reached at top dead centre of the crank. This would allow the crank to pass beyond top dead centre, which would allow the crank to operate from different sides of the crankshaft to promote better lubricant circulation in the bearings. If the system is used in a configuration in which the crank does not reach top dead centre when the first and second sealing tools are pressed together, then a method of operating the system may involve changing the side of the crankshaft from which the crank is driven during maintenance and/or changes of the sealing tools being used.
The present invention is particularly advantageous in cases in which the actuator comprises a motor. Motors are typically more cost-effective than pneumatic actuators, but cannot provide accurate data as to the force they are exerting. A typical motor powered arrangement would involve a motor and a crankshaft, with the sealing tool coupled to the crankshaft so that the rotational movement of the motor is translated into a linear motion of the sealing tool for pressing against the opposing sealing tool. In some embodiments, the system will be calibrated so that the desired seal pressure is reached at the extreme of the movable range of the sealing tool (for example, by means of the adjustable support beam described above), as this will correspond to top dead centre of the crank. This will allow the sealing tools to be held in this position for sealing while benefiting from the alignment strength of top dead centre of the crank. However, as mentioned above, in some embodiments of the invention, the strain gauge measurements may be used by a controller to control the movement of a sealing tool until the desired pressure is reached. In such cases, the desired sealing position will not typically correspond to top dead centre of the crank. This can lead to increase wear of the actuator mechanism as it is held under high pressure without benefitting from the alignment strength of top dead centre. Therefore, in some embodiments, the motor is provided with a self-locking gear box, for example comprising a self-locking worm gear. This ensures that variation in the movement distance of the sealing tool does not increase wear on the actuator.
In systems comprising a motor, preferably the motor is configured to measure the motor torque. For example, the motor may comprise a torque sensor for measuring the torque generated by the motor or this may be output directly from the motor controller. Motor torque alone is not enough to determine the seal pressure; however, in combination with measurements from the strain gauge, a comparison of force transmitted through the frame and torque generated by the motor can be useful for diagnosing problems with the system. Further preferably, the system comprises an encoder for measuring displacement of the actuator. Similarly to motor torque, the displacement of the actuator is not enough to determine sealing pressure, but again the combination with the strain gauge measurements provides useful diagnostic insights. For example, low seal force and high motor torque can indicate that there is a problem with the sealing tools, low seal force and low motor torque may indicate a problem with the motor, or high displacement for a given sealing force can indicate a problem with sealing tool silicone
While it is possible that both sealing tools could be driven by a respective actuator, or even the same actuator, preferably only one of the sealing tools is driven by an actuator. The other tool may be fixed, or may move passively as the driven tool is pressed into it. In particular, one of the first and second sealing tools may be coupled to the actuator and the other of the first and second sealing tools may be substantially fixedly mounted relative to the frame, preferably substantially fixedly mounted to the frame. It should be noted that while one tool is preferably substantially fixed relative to the frame, this may still involve elements within that tool that moving during sealing, but any movement is preferably passive movement, i.e. not powered by an actuator, such as movement of one or more elements of the tool on resilient connections, such as springs, in response to the pressure of the opposing actuated tool. In these cases, nonetheless, the fixed sealing tool should still feature a fixed mounting, e.g. to the frame. Providing that only one of the sealing tools is driven by an actuator significantly reduces the complexity of the system while still permitting an accurate reading of seal force using the strain gauge.
Where only one tool is movable by an actuator, preferably, it is the first sealing tool that is fixed to the frame, i.e. the sealing tool that is mounted to the support beam or which features a strain gauge located at its mounting point to the frame.
Preferably, the first or second sealing tool comprises a tool body and one or more sealing portions movable relative to the tool body, wherein in a first movement phase the actuator is configured to bring the first sealing tool into contact with the second sealing tool, and wherein in a second movement phase the actuator is configured to cause the sealing portion to move relative to the tool body so as to press the sealing portion of said sealing tool against the other of the first and second sealing tools. For example, where the system is a tray or skin sealing system, the movable tool may be the lower tool that holds the tray or support in the sealing portion. The actuator may be configured to raise the whole lower in a first phase to clamp the sealing film between the two tools. Pressing the lower sealing tool into the upper sealing tool may then cause elements to move relative to one another, e.g. on springs, for sealing the film to the container. In this way, a single actuator can be responsible for both the tool closing and sealing processes, reducing the cost and complexity of the system. In this example, the strain gauge may make a first measurement at the end of the first movement phase and a second measurement at the end of the second movement phase. It may be necessary to determine the difference between two or more measurements to distinguish the seal force from, for example, the force as a result of clamping the film between the two tools.
Many embodiments further comprise a controller, wherein the controller is connected to the at least one strain gauge and is configured to output an indication that the system is defective based on the measurements of the strain gauge, such as when a peak measurement by the strain gauge as the first and second sealing tools are pressed together falls above or below a predetermined value, preferably when the peak measurement falls outside of a predetermined range. This is particularly preferred in a system in which the actuator comprises a motor and crankshaft configured to hold the tool at top dead centre to form a seal, as a lower seal pressure than expected can mean inadequate seals are formed, whereas a higher seal pressure than expected can cause accelerated wear of various components of the system. Outputting an indication that the system is defective may comprise one or more of an audible alarm, an alert on a screen, or ceasing operation of the system.
Where the system comprises a torque sensor and/or an encoder, preferably the controller is connected to the at least one strain gauge and the torque sensor and/or encoder, and the controller is configured to output an indication that the system is defective based on the measurements of the strain gauge in combination with the measurements of the encoder and/or the torque sensor, wherein preferably the controller is configured to output an indication that the system is defective based on a comparison of the measurements of the strain gauge with the measurements of the encoder and/or the torque sensor across a plurality of sealing cycles. For example, in some systems, the controller may control the motor so that the same seal pressure is always reached. This may involve gradually increasing the linear movement over many cycles as the system wears, and so monitoring only the measurement of the strain gauge may not identify a problem with the system. A large change in linear movement for the same seal pressure may indicate a problem with the system, which the controller can identify by comparing these measurements across a number of successive sealing cycles. Alternatively, excessive peak of torque for the same seal pressure may highlight a problem with the tool lift and main bearings. The system may also identify when a sealing stroke is requiring the actuator to move to top dead centre to achieve the desired seal pressure, or within a predetermined distance, such as 1 mm, of top dead centre using the encoder, and may indicate a problem, such as with the tool silicone.
As noted above, a particular type of sealing system that benefits from the invention is one in which 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, wherein the lower tool is configured to receive and hold a container for sealing and the upper tool is configured to seal a lid, preferably a film lid, on 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 a film lid to the container along a sealed seam. Further preferably, the upper tool comprises a cutting tool for cutting out a lid of the container from a web of material. Particularly preferably, the cutting tool is connected to the heat-sealing tool via one or more resilient members, such that pressing together of the upper tool and the lower tool causes relative movement between the cutting tool and the heat-sealing tool. This allows separate cutting a sealing phases and can be used, for example, to ensure the film is cut and then sealed without the cutting tool contacting the tray or support. Further, these two sealing phases, including relative movement, can be again provided only by movement of the lower tool, ensuring there is not the need for additional drive means for the top tool.
According to a second aspect of the invention, a method of sealing food containers comprises: providing a food container to be sealed between a first sealing tool and a second sealing tool, the first sealing tool being mounted to a frame at least at a first mounting point so as to be supported by the frame; pressing the first and second sealing tools together so as to seal the food container positioned therebetween; measuring a force transmitted through the frame as the first and second sealing tools are pressed together using at least one strain gauge attached to the frame. In alternative systems, it is foreseen that the strain gauge may be positioned between the frame and the first sealing tool at the first mounting point.
This aspect corresponds to a method of sealing a container using the system according to the first aspect. All of the preferred features discussed above with respect to the first aspect may equally be employed in this method of sealing.
In particular, the method preferably comprises pressing the first and second sealing tool together based on the measurements of the at least one strain gauge, wherein further preferably the first and second sealing tools are pressed together such that a peak measurement by the strain gauge exceeds a predetermined threshold or falls within a predetermined range.
The method may also comprise outputting an indication that the system is defective when a peak measurement by the strain gauge as the first and second sealing tools are pressed together falls above or below a predetermined value, preferably when the peak measurement falls outside of 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 generated by the motor, and outputting an indication that the system is defective based on the measurements of both the strain gauge and the torque sensor, preferably based on a comparison of the measurements of the strain gauge and the torque sensor across a plurality of sealing cycles.
The invention will now be described with reference to the accompanying drawings, of which:
An example system will now be described with reference to
The sealing unit 20 is located in a central portion of the system 1. The sealing unit comprises an upper sealing tool 21, which is substantially fixedly mounted to the frame 100, although will typically comprise movable parts within the upper tool. This sealing unit is configured to perform tray or skin sealing, and so the upper sealing tool 21 will typically comprise a heat-sealing plate for heat sealing the film to the rim of a tray or other support, and a cutting tool for cutting out an area of the film that is sealed to the tray or support. The lower sealing tool 22 will typically comprise a receiving portion, configured to receive a tray or support to be sealed. The actuator may lift the lower sealing tool and press the lower sealing tool 22 against the upper sealing tool 21 to cause sealing to occur. Once the upper and lower sealing tools are closed, the actuator may further lift the lower sealing tool, which may cause relative movement of components within one or both of the upper and lower sealing tools. For example, the upper tool may comprise a heat-sealing plate and a cutting tool mounted on springs to a body or housing of the upper sealing tool, such that upward movement of the body or housing of the upper sealing tool as it is pressed by the lower tool causes the heat-sealing plate and the cutting tool to project from the body or housing of the upper sealing tool and contact the tray. Such an arrangement of a heat-sealing plate and cutting tool within an upper sealing tool is described in co-pending application PCT/GB2021/052230.
The sealing process is illustrated in
As can be seen in
Alternatively to what is shown in
The frame 100 comprises a number of frame elements surrounding and supporting the sealing unit 20. Immediately upstream of the sealing unit 20 are first and second frame elements 101, 102 that together define a closed loop. In particular, the second frame element is a single sheet of metal that defines a horizontal base portion 102a of the frame. This base portion extends across the width of the system, below the sealing tools 21, 22. At the rear side of the system, or the right side in
As will be described in more detail below, the upper sealing tool 21 is supported by the upper frame portion 102c and the lower sealing tool 22 is supported by the lower frame portion 102a so that, when the sealing tools are pressed together, the vertical frame portions 102b, 102d and the first frame element 101 are under tension as the frame resists the sealing forces. A strain gauge 122 is provided on the first frame element 101, which measures the tension force in the first frame element. The strain gauge may be, for example, a two-hole bolt-on strain gauge sensor, as produced by Datum Electronics of Datum Global HQ, Castle Street East Cowes, Isle of Wight PO32 6EZ. By providing the strain gauge on the detachable first frame element 101, this may be easily removed from the wider frame for repair or replacement. Furthermore, by providing the strain gauge on an element that is parallel with the direction along which the sealing tools are pressed together, and is in pure tension, it is more straightforward to understand the sealing forces.
While it would be possible for frame elements defining a single closed loop to support the tools, in the present embodiment a further frame element 104 is provided that defines a second closed loop. This frame element is parallel to the first and second frame elements and is provided immediately downstream of the sealing unit 20 along the conveying direction. While, in this embodiment, the second closed loop 104 is defined by a single element, this could also be formed like the first closed loop by two frame elements, which would allow another strain gauge to be provided on a detachable frame element within the second closed loop.
As mentioned above, the frame also comprises a horizontal beam 103 that extends between these two closed loops, above the upper sealing tool 21. On the downstream face of the second frame element 102, above the beam 103, there is a connection point 103a in the form of a bracket having two vertical screw holes. The beam 103 is coupled to the second frame element at an upstream end of the beam 103 by jack screws that pass through the screw holes in the bracket and are received in the beam 103. An equivalent connection point 103b is also provided on the upstream face of the further frame element 104 for connecting the downstream end of the beam 103 to the frame element defining the second closed loop. As noted above, the upper sealing tool 21 is connected to a lower surface of the beam 103 at first and second mounting points 21a, 21b. These may comprise bolts that pass through openings in the beam 103 and are received in mounting pillars of the upper sealing tool 21. Between the two mounting points 21a, 21b on the beam 103 may be provided another strain gauge. This strain gauge may be of the same type described above, or may be a more sensitive strain gauge to detect smaller variations in elongation. Alternatively, or additionally, a strain gauge could be positioned between the beam 103 and the upper sealing tool at one or both of the mounting points 21a, 21b.
The frame 100 also comprises a lower tool mounting element 105. The mounting element 105 extends between the two closed loops below the lower sealing tool 11. In particular, the frame element 105 is connected to the lower frame portion 102a of the second frame element 102 via a connection 105a, and is connected to a lower portion of the further frame element 104 via a connection 105b. As mentioned above, the lower sealing tool 22 is coupled to the crank arm 27, which is connected to the motor 26 of the actuator 25 via a crankshaft. The actuator 25 is connected to the frame mounting element 105 at via connection point 25a.
By this arrangement of the sealing tools 21, 22 on the frame, as the sealing tools are pressed together, the sealing forces are transmitted into the two closed loops of the frame. In particular, as the upper sealing tool is pressed upwards, this is resisted by the beam 103, which is connected at its opposing ends to the frame element 102 on the upstream side and the further frame element 104 on the downstream side. Similarly, as the actuator presses the lower sealing tool upwards, the opposing force is transmitted into the frame element 105 and then to the frame element 102 on the upstream side and the further frame element 104 on the downstream side. Accordingly, the sealing forces are transmitted through the two closed loops of the frame.
In principle, a strain gauge may be provided on any of the frame elements 101, 102, 103, 104 and 105. However, it is preferred to provide strain gauges in areas that undergo significant deflection or tension during sealing. As has already been mentioned, the first frame element 101 is part of one of the arms connecting the upper and lower frame portions that are part of the closed loop, through which the sealing force is transmitted. This element will be in pure tension during sealing and so is a suitable place for a strain gauge. The beam 103, on the other hand, being perpendicular to the direction along which the sealing tools are pressed together and being directly above the upper sealing tool 21 will experience significant deflection during a sealing process. This deflection may be enhanced by making the beam 103 of a thinner and/or more flexible metal than the other frame elements that resist the sealing forces. For example, the beam 103 may be made of stainless steel 304 and may have a thickness of 5 mm In contrast, the other frame elements may be made of stainless steel 304 and may have a thickness of 10 mm
Wherever the strain gauge is positioned on the frame, the strain gauge may need calibrating before it can be used with any particular tool installed in the system during normal use. This calibration may comprise installing the tool that is intended to be used in the system and then placing a load cell in to the tool. The actuator may then be used to press the tools together with the load cell therebetween to a range of forces as detected by the load cell. The output from the strain gauge is recorded as the tools are pressed together and the strain gauge output plotted against the measured forces from the load cell, from which can be derived a relationship between the strain gauge measurements and the seal force, typically in mV·kN−1. Finally, the load cell may be removed and one or more trays placed in the tool for sealing. The tools may be slowly pressed together until the desired sealing force is reached, as determined by the strain gauge measurements in combination with the relationship that was determined using the load cell. As mentioned previously, the desired seal force will vary from one tool to the next depending on the type of seal being produced, the number of trays sealed at once, and the total sealing area of each tray. Once the desired sealing pressure is reached for a particular tool, the position of the actuator is stored for future sealing strokes.
A method of operating one of the disclosed systems will now be described with reference to
In a first step S100, a food container to be sealed is provided between the bespoke change part tooling in the upper and lower sealing tools 21, 22. In this phase, the system should be arranged as shown in
In a second step, S200, the actuator 25 is used to raise the lower sealing tool 22 and bring it into contact with the upper sealing tool 21. This will clamp the film and the container to be sealed between the two sealing tools 21, 22. This corresponds to the position shown in
From this point, in step S300, the system may monitor the readings of the strain gauge 121, 122 to determine the force being transmitted through the frame. While this step is shown as occurring before the subsequent step S400, it should be appreciated that measuring by the strain gauge 121, 122 will preferably continue through the sealing process. It should also be noted here that, if the actuator 25 comprises a motor 26 with a torque sensor and an encoder, the method may comprise monitoring the strain gauge measurements, encoder position and the torque sensor measurements. Generally, these will correlate between calibration and sealing cycles, but any deviation in one relative to the other may be an indication of a system failure, which may be used to output an indication that the system requires maintenance or is defective and stop the system.
In step S400, the actuator 25 is used to press the lower sealing tool against the upper sealing tool and cause sealing of the food container. This may comprise pressing the tools together until a desired sealing pressure is reached, as determined by the measurements of the strain gauge 121, 122. Alternatively, in faster systems, this may comprise pressing the tools together based on the appropriate actuator position determined during calibration, and the measurements of the strain gauge used to validate the sealing process and monitor for signs of errors. In another alternative, the system may have been calibrated and configured so that the desired sealing pressure is reached at top dead centre of the crank arm 27. This is shown in
In step S500, the actuator 25 is used to open the sealing tools. If the desired sealing pressure is being reached at top dead centre, then the crank arm may be moved to the opposite side of the crankshaft from which it started in order to even the wear on the bearings.
Finally, in step S600, the sealed container or containers are removed from the lower sealing tool. Grippers arms may be used to transfer the sealed container to the conveyor belt 42. Then the process returns to step S100 for sealing of further food containers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2202361.8 | Feb 2022 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2023/050237 | 2/3/2023 | WO |
