Patent Application
20230182193
The present invention relates to the monitoring of can bodymakers. In particular, it relates to an apparatus and method for monitoring the forces acting on components in a tool pack of a can bodymaker when the can bodymaker is operated.
In known can bodymakers for the production of thin-walled metal two-piece can bodies by a “drawing and wall-ironing” (DWI) process, metal cups are fed to the bodymaker and carried by a punch on the end of a ram through a series of dies to produce a can body of the desired size and thickness. The series of dies may include a redraw die for reducing the diameter of the cup and lengthening its sidewall, and one or more ironing dies for wall-ironing the cup into a can body. The area or cradle of the bodymaker frame within which the dies are located is known as the “toolpack”. The can body carried on the punch may ultimately contact a bottom forming tool or “domer” so as to form a shape such as a dome on the base of the can. An exemplary bodymaker is described in WO9934942.
Can bodymakers are typically operated for extended periods at high speed to produce more than around 300 to 400 can bodies per minute. However, the quality of the can bodies that are produced can vary significantly over time because of changes in, for example: the alignment of the machine components, coolant temperature and flow rate, lubrication of the machine, and/or the quality of the incoming cups (e.g. because of variations in the quality of the metal coil from which the cups are made).
During the DWI process, the metal is subject to loads as the punch forces it through the ironing dies. However, the magnitude and distribution of these loads changes both during the stroke, and from stroke to stroke, leading to variations in the quality of the can bodies produced. For example, frictional forces and general wear will cause the alignment of the ram to vary slightly over time. In addition, a high speed reciprocating ram is generally subject to at least some vibration, due to the impact of the ram on the can body and to the variable “droop” of the ram as it moves from and to its fully-extended position.
As a further example, when the ram carries the can body into contact with the domer, any misalignment can lead to the can body end splitting, particularly if the can body is made from aluminium. If the misalignment is slight, the split (sometimes known as a “smile”) may not be immediately visible to the naked eye, and the split may lead to the can bursting once the can body has been filled. This may not occur until the filled can has been purchased.
Poor quality can bodies may lead to wastage and downtime in can production. This may occur, for example, either because the bodymaker itself must be re-aligned or repaired or because other machines further down the production line are adversely affected by the poor quality cans being produced. Unfortunately, the high speed, high volume nature of the can production industry means that lost production time can be very costly for producers.
Traditionally, alignment and re-alignment of bodymakers is a complex and time-consuming process that needs to be carried out laboriously by skilled operators (who are often in short supply) only after serious problems have developed. When setting up a can bodymaker, the ram and its drive components are typically fixed in place on the bodymaker frame. This aligns the axis of the ram with the main axis of the bodymaker. The other components, including for example the redraw and ironing dies and domer, are then aligned with the ram.
According to a first aspect of the present invention there is provided a can bodymaker for producing can bodies from cups. The can bodymaker comprises a ram configured to reciprocate along an axis, a punch mounted on the ram; a tool pack comprising a cradle and a plurality of tools located in the cradle for drawing and ironing a cup mounted on the punch during a forward stroke of the ram. The can bodymaker further comprises a bolster plate fixed to the can bodymaker, an adapter plate fixed to the bolster plate and a stripper assembly fixed to the adapter plate for removing a can body from the punch during a return stroke of the ram and clamping mechanism for biasing the tools against a front face of the adapter plate. The can bodymaker further comprises one or more load cells located in or on the adapter plate and configured to generate an output signal or signals indicative of an axial force exerted on the tools by the cup passing therethrough.
The term “axial force” means a force having a component directed along the axis along which the ram reciprocates.
The can bodymaker may comprise an encoder configured to provide a measurement of the position of the ram at one or more times during each reciprocation. The encoder may be a linear encoder. Alternatively, the encoder may be a rotary encoder configured to be turned by a shaft used to drive the ram.
The one or more the load cells may be piezoelectric load cells.
The one or more load cells may comprise more than one load cell, the load cells being angularly spaced apart from one another equally about the axis.
The can bodymaker may comprise a processor configured to adjust one or more operating parameters of the bodymaker, such as a rate of reciprocation of the ram, in response to the output signal(s).
The adapter plate may be fixed to the bolster plate by one or more preloading bolts, each preloading bolt passing through a respective one of the load cells to secure the load cell between the adapter plate and the bolster plate,
The stripper assembly may comprise a radial offset monitor for detecting misalignment of the ram and/or punch relative to the axis.
The radial offset monitor may comprise a bore configured to allow passage of the punch and ram therethrough and one or more eddy current sensors spaced around the bore.
According to a second aspect of the present invention there is provided an apparatus for retro-fitting to a can bodymaker. The can bodymaker comprises: a ram configured to reciprocate along an axis; a punch mounted on the ram; a tool pack comprising a cradle and a plurality of tools located in the cradle for drawing and ironing a cup mounted on the punch during a forward stroke of the ram; a bolster plate fixed to the can bodymaker; an adapter plate fixed to the bolster plate; a stripper assembly for removing a can body from the punch during a return stroke of the ram; and a clamping mechanism for biasing said tools against a front face of the adapter plate. The apparatus comprises: a replacement adapter plate for fixing to the bolster plate in place of the adapter plate of the can bodymaker; and one or more load cells located in or on the replacement adapter plate and configurable to generate an output signal or signals indicative of an axial force exerted on the tools by the cup passing therethrough.
The replacement adapter plate may include a stripper assembly comprising a radial offset monitor for detecting misalignment of the ram and/or punch relative to the axis.
The radial offset monitor may comprise a bore configured to allow passage of the punch and ram therethrough and one or more eddy current sensors spaced around the bore.
According to a third aspect of the present invention there is provided a method of calibrating the apparatus the second aspect after it has been retro-fitted to a can bodymaker. The method comprises installing into the cradle of the can bodymaker, a calibration fixture comprising one or more reference load cells configured to generate an output signal or signals indicative of an axial force exerted on the tools located in the cradle. An axial force is applied to the tools and one or more reference load cells using the clamping mechanism of the can bodymaker. The respective output signal or signals of the reference load cell(s) are used to determine a calibration factor or calibration function for estimating the force on the tool(s) from the output signals generated by the load cell(s) of the apparatus.
According to a fourth aspect of the present invention there is provided a method of operating a can bodymaker to mitigate the effects of tool wear, damage and/or misalignment during production of can bodies. Each can body is formed by pushing a cup mounted on a punch of a ram reciprocating along an axis through tools contained within a cradle of a tool pack of the can bodymaker. The method comprises obtaining, from one or more load cells, output signals indicative of an axial force exerted on the tools by the cup passing therethrough, the load cell(s) being located in or on an adapter plate attached to a bolster plate fixed to the can bodymaker. The output signals are processed to obtain data indicative of one or more of the tools being worn, damaged, and/or misaligned with respect to the ram. One or more operating parameters of the can bodymaker, or of another component of a production line within which the bodymaker is located, are adjusted based on said data to mitigate the effects of the one or more tools being worn, damaged, and/or misaligned with respect to the ram.
The one or more operating parameters may comprise one or more of:
The one or more operating parameters may comprise a parameter of a component of the production line upstream or downstream of the bodymaker, for example a cup press.
The method may comprise removing the can body from the punch during a return stroke of the ram using a stripper fixed to the adapter plate.
The stripper may be provided in a stripper assembly comprising a radial offset monitor, and the method further comprises obtaining output signals indicative of a position of the ram and/or punch perpendicular to the axis using the radial offset monitor and adjusting said one or more operating parameters based on the data and the output signals obtained from the radial offset monitor.
The tool pack 107 also comprises a redraw sleeve module 112, located in front of the redraw die (not shown) for positioning the cup during the redraw process. The redraw sleeve module 212 comprises a bearing 113 with a cup locator (not shown) to receive a cup from an infeed mechanism 114 of the infeed-discharge module 111. The bearing 113 supports a reciprocating redraw sleeve 115 that is aligned coaxially with the ram and has a central bore that allows the punch to pass therethrough. A rear end of the redraw sleeve 115 is coupled to a redraw carriage 116 that is driven in a reciprocating motion by a pair of push rods 117a, 117b located on opposite sides of the ram 106. Prior to the punch contacting the can, the redraw sleeve 115 enters the open end of the cup and forces the cup into contact with the redraw die. The redraw sleeve 115 holds the cup firmly in place against the redraw die as the punch pushes the cup through an aperture of the redraw die that is of smaller diameter than the cup. As the cup is drawn through the redraw die by the punch it reduces in diameter and its sidewall lengthens. The tool pack 107 may also contain one or more ironing dies or other tooling for forming the can body after the redraw die. The punch then carries the elongated cup away from the redraw sleeve module and through the remaining ironing dies and tooling.
The stripper assembly 221 comprises a stripper 233 mounted within a stripper housing 235 that is attached to the adapter plate 225. The stripper 233 comprises stripping fingers that extend radially inwards, i.e. towards the axis A-A′. On the forward stroke of the ram 106, the can body carried on the punch deflects the stripping fingers as it moves through the stripper 233. On the return stroke, i.e. away from the bottom forming tool 108, the stripping fingers prevent the can body from returning with the punch and the can body is stripped from the punch and then removed from the bodymaker 201 by the can discharge turret 210. In other embodiments not shown here, the can body may be removed from the bodymaker 201 by pressurised air (alternatively, pressurised air may be used to assist removal of the can body by a stripper).
The adapter plate 225 is located between the bolster plate 223 and the toolpack housing 219. The adapter plate 225 comprises three load cells 237A-C (see
The annular body 301B of each load cell 273A-C is located in a recess formed in the edge and rear face of the adapter plate 225 (i.e. the face of the adapter plate 225 furthest from tool pack cradle 220). In this example, each recess is shaped to accommodate a wired connection to the side of the annular body 301 B. The load cell 237A also comprises a preloading bolt 301 B that passes through the adapter plate 225, through the centre of the annular body 301 and into the bolster plate 223. The cylindrical body 301A protrudes from the recess so that it contacts the bolster plate 223 across a small gap between the adapter plate 225 and the bolster plate 223 (see
In the particular embodiment shown in
Returning to
The load cells 237A-C may be provided about the axis A-A′ in an equiangular arrangement to provide optimal sensitivity. A minimum of three load cells 237A-C is preferred to provide sufficient spatial detail and the maximum number of load cells 237A-C is limited only by cost and the space available within the adapter plate 225. Other types of load cells 237A-C, such as capacitive load cells, can also be used instead of or in addition to piezoelectric load cells.
The adapter plate 225 may be retrofitted to existing can bodymakers without modification to the toolpack, e.g. by replacing an existing adapter plate.
As the load cells 237A-C are located outside of the cradle 220, force measurements can be made without requiring any reconfiguration or replacement of the components (tools) in the cradle 220. For example, although a fixture with the load cells 237A-C could in principle be installed in place of one of the spacer rings, this would require that the fixture to be manufactured to a high tolerance and multiple versions of the fixture may be needed depending on which dies are included in the toolpack. Such an arrangement may also adversely affect the cooling provided to the dies. Including the load cells 237A-C inside the cradle 220 may also be problematic because installing and removing components from the cradle 220 may be liable to damage the load cells 237A-C.
Although force measurements can be made with a single load cell 237A it is preferable to have more than one transducer in order to obtain information about how the forces acting on the dies are distributed spatially. For example, multiple load cells 237A-C may be used to determine that the relative alignment between the ram/punch and one or more of the dies needs correcting, e.g. using an iterative procedure in which the forces measured by each of the load cells 237A-C are compared and the alignment of the ram and/or dies varied until the forces are balanced, and/or until each of the measured forces is minimised. In practice, this procedure can be carried out by using a computer device (not shown) comprising an analogue to digital (ADC) converter to process the time-varying electrical signals generated by the load cells 237A-C and to generate a graphical display or readout of the forces that can be viewed by an operator who is making the necessary adjustments.
In some case, the computer device can be configured to detect when the forces exceed a threshold and/or whether there is an imbalance in the measured forces (e.g. one of the measured forces is greater than the others) exceeding a threshold, and respond by generating a visual or audible alarm and/or halting operation of the can bodymaker 201.
The computer device may also control one or more operating parameters of the can bodymaker 101 to ensure that it operates safely and efficiently. For example, the computer device may reduce the repetition rate of the can bodymaker 101 once a problem has begun to develop.
The time-varying measurements obtained from the load cells 237A-C can be logged (e.g. stored in a database) so that gradual changes in the alignment caused by wear and vibrations can be monitored. The time resolution provided by the ADC is sufficient to resolve the temporal variation of the forces measured in the course of a single stroke. This data may be correlated with longitudinal position data for the ram over the course of each stroke (i.e. data indicative of the rams motion along the axis A-A′). This data may be obtained, for example, from a high-resolution rotary encoder that is turned by the shaft used to drive the reciprocating ram, or from a high-resolution rotary encoder that measures the longitudinal position of the ram more directly. Correlating the force measurements with the position data allows particular features in the force measurements to be attributed to passage of the ram through particular components of the toolpack, allowing e.g. a particular die to be identified as poorly aligned or damaged, or for the wear on each of the dies to be estimated from the total force on each die integrated over a large number of strokes. This analysis may be performed automatically by the computer device, which may generate a warning signal or alert indicating that one or more of the dies needs re-aligning or replacing. The stroke number may also be recorded so that the measured force data can be associated with a particular can or cans produced by the bodymaker 201, e.g. so that particular cans or batches of cans can be certified as likely to be free of defects or otherwise prevented from being shipped to customers.
It is not essential for the load cells 237A-C to be calibrated because useful information can still be obtained from the relative forces measured by each of the load cells 237A-C (e.g. to detect changes in the relative alignment of the components over time). Nevertheless, calibration of the load cells 237A-C may allow more accurate models of the forces acting on the dies to be constructed, thereby allowing more sophisticated processing of the measurements to be performed and potential problems to be detected earlier. Calibration refers here to the conversion from the electrical signal produced by the load cells 237A-C and the actual longitudinal forces acting on the toolpack components. This may involve determining a mathematical conversion function that takes the electrical signal(s) as an input and provides corresponding force(s) as an output. In some cases, this function may consist of a multiplicative factor used to scale the electrical signal by an amount. Calibration is, in general, needed for accurate measurements because the proportion of the force transmitted to the load cells 237A-C will vary according to how the adapter plate 225 is mounted and/or because the transmission of the forces from the dies may vary according to how the toolpack is configured, e.g. what “pre-load” is applied to the toolpack (see below).
To calibrate the load cells 237A-C, a fixture comprising one or more reference load cells (not shown) may be installed into the cradle 220 (e.g. in place of one of the spacer rings or ironing dies). A load is then applied to the reference load cell(s) along the axis A-A′ and the electrical signals produced by the load cells 237A-C and the reference load cell(s) measured. The conversion function is then determined from the measured signals, e.g. by fitting a polynomial or spline interpolation function to the reference signals plotted against the load cell signals. The load applied to the reference load cell(s) and the load cell(s) 237A-C may be generated by the toolpack clamp 241 (see
compensate for) variances in the pre-load between can bodymakers. Calibration of the load cells 237A-C also allows the proportion of the longitudinal load that bypasses the load cells 237A-C through the preloading bolt 301 B to be compensated.
The force measurements obtained from the load cells 237A-C during can production can be analysed using machine learning, analytics and/or artificial intelligence techniques to determine how the operation of the can bodymaker can be improved, e.g. by adjusting one or more operating parameters of the can bodymaker. For example, an evolutionary algorithm (or another type of optimisation algorithm) can be used to vary operating parameters of the can bodymaker according to a fitness metric based on the measured forces, e.g. a fitness metric that penalises the measured forces exceeding a pre-defined threshold and/or the forces measured by the load cells 237A-C differing from one another by a predefined threshold or relative proportion.
The operating parameters for the can bodymaker that are provided to the algorithm may include one or more of: the rate of can production (set speed of the can bodymaker), the operating temperature of the toolpack, the rate at which coolant is supplied to the toolpack, the rate at which lubricant is supplied to the toolpack, and the domer position (alignment) with respect to the ram axis. The algorithm may also take as an input other types of data, such as the time elapsed since the can bodymaker was last serviced or reconfigured, the number of cans produced using the current set of dies, and/or a measurement of the quality of the feedstock, such as the thickness or weight of the cups supplied to the bodymaker.
Feedback control can also be used to adjust one or more of the can bodymaker operating parameters in order to compensate for changes to the can bodymaker over time caused by wear or movement of the components in the can bodymaker. For example, a proportional-integral-derivative (PID) controller can be used to vary one or more of the can bodymaker operating parameters to minimise an error signal determined from the measured forces.
It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007230.2 | May 2020 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/062064 | 5/6/2021 | WO |
