WO2018184959A1

WO2018184959A1 - Optimising the performance of mixing machines

Info

Publication number: WO2018184959A1
Application number: PCT/EP2018/058012
Authority: WO
Inventors: Oliver FAIR; Padraic Timon
Original assignee: Chameleon Colour Systems Limited
Priority date: 2017-04-03
Filing date: 2018-03-28
Publication date: 2018-10-11
Also published as: GB201705360D0; EP3606652A1

Abstract

The performance of a mixing machine for mixing paints and other fluid bodies is monitored by powering a mix drive and/or a clamp drive in accordance with a program. Torque applied by a motor that powers either of those drives while executing the program is monitored and the program may be modified accordingly. For example, mixing speed and mixing duration may be changed if the level of, or fluctuation of, torque applied by a mix motor suggests that the fluid body has characteristics, such as mass, for which the initially-selected mixing program is inappropriate. Similarly, torque applied by a clamp motor may be monitored to determine maintenance issues and to detect if a container carrying a fluid to be mixed is being crushed under clamping pressure.

Description

Optimising the performance of mixing machines

This invention relates to machines for mixing fluid materials by agitation, including viscous liquids and dry powders that behave as a fluid mass when agitated.

Mixing machines in accordance with the invention include mixers and shakers that can be used to mix liquids such as paints, pigments or inks, or dry particulates or powders such as plaster. For example, it has become common to offer paint mixing at the point of sale. This allows a very wide range of paint colours to be offered for colour-matching purposes without having to stock a correspondingly large number of pre-mixed paints.

To produce paint of a desired colour, one or more appropriate pigments, colourants or tints are added to paint of a basic colour held in a container, such as a can of metal or plastics. The container is then closed and placed in a mixing machine that agitates the container for a period long enough to mix the contents of the container thoroughly. The contents do not fill the container completely; a small headspace is left so that there is room for the contents to slosh or otherwise flow within the container to promote mixing. Conveniently, the resulting paint mixture may be sold in the container in which it is mixed.

Two main types of mixing machines are used for mixing paints at the point of sale, known in the art as gyroscopic mixers and vibrational shakers. They employ principles of agitation that may also be used to mix paints, inks or other fluid materials on an industrial scale.

Known gyroscopic mixers comprise a clamp mechanism for clamping one or more containers and a mix motor to rotate the clamp mechanism, and hence a clamped container, around a primary axis. Simultaneously, the clamp mechanism rotates the clamped container around a secondary axis transverse to the primary axis. Thus, the container is tumbled by being inverted repeatedly while being turned around its longitudinal axis during a mixing cycle.

Typically the clamp mechanism comprises a pair of clamp plates that are opposed to each other about the primary axis. The clamp plates can be moved toward or away from the primary axis to vary the spacing between them, hence to clamp a container between them for mixing or to release the container after mixing. Preferably, the opposing movements of the clamp plates are synchronised and substantially symmetrical about the primary axis to maintain rotational balance.

Known vibrational shakers also comprise a clamp mechanism for clamping one or more containers. A mix motor rotates an eccentric drive shaft that shakes the clamp mechanism and hence shakes a clamped container supported by the clamp

mechanism. In this case, however, the container remains in a generally upright orientation and is neither inverted nor rotated during a mixing cycle. The clamp mechanism of a typical vibrational shaker comprises a lower clamp plate that supports the container and an upper clamp plate that is lowered to clamp the container against the lower plate for mixing. After mixing, the upper clamp plate is raised so that the container can be lifted from the lower clamp plate for removal from the machine.

In both cases, it is desirable for the mixing machine to be able to handle containers of various sizes. It is also possible for the mixing machine to handle two or more small containers side-by-side so as to mix the contents of those containers simultaneously. Thus, the clamp plates are wide enough to accommodate one or more containers of various widths and the variable spacing between the clamp plates allows the clamp mechanism to apply clamping pressure to containers of various heights or lengths.

Also, it is desirable for a mixing machine to offer different mixing speeds to suit different containers. Generally the mixing speed is inversely proportional to the size of the container; thus, the larger and heavier the container, the slower the mixing speed.

Similarly, the mixing speed should be reduced if operators choose to place two or more containers between the clamp plates side-by-side.

It is important to use mixing machines correctly in view of the substantial kinetic energy in a heavy container being agitated quickly. For example, when mixing paint, it is important that the mixing speed is appropriate for the weight and size of the paint can being used and for the viscosity of the paint being mixed. If paint in a large or heavy can is mixed at a fast speed setting intended for a small or light can, the mixing machine may be subjected to excessive loadings. The machine may suffer excessive wear or damage as a result. In theory, correct operation of a mixing machine could be assured by using an automatic control system that is responsive to signals from sensors in the machine. In practice, however, the effectiveness of such a control system depends heavily upon the degree to which the containers that are used in the mixing machine are standardised and so have predictable characteristics. In the real world, the effectiveness of such a control system is also undermined by the human factor due to operator behaviour.

For example, in principle, the size of a paint can of standard proportions can be inferred from its height, which in turn can be inferred by determining the spacing between the clamp plates when they clamp the can. The likely weight of that can may then be assumed by knowing the typical volume and density of paint that such a can will typically hold. The mixing speed can then be limited accordingly, preferably automatically. However, it is not straightforward to sense other parameters that may have a bearing upon rotational imbalance, including the relative weights of multiple containers or the extent to which a container may have been placed off-centre between the clamp plates.

In particular, where a paint mixing machine will encounter only a limited range of paint cans, an appropriate program of operation could be chosen simply by measuring the spacing between the clamp plates when a can has been clamped. In practice, however, such a system would fail to choose the correct program if a can is of nonstandard proportions, or if the can contains an unexpectedly small volume of paint, or if the can contains fluids of an unexpected density, or if two or more small cans are placed beside each other in the clamp mechanism.

Additionally, the clamp plates of a mixing machine are generally oversized to accommodate a variety of container widths or to allow small containers to be mixed side-by-side. This introduces the risk that the mixing machine will be subjected to off- axis loading conditions and hence excessive vibration, which is a challenge that is prevalent in the industry.

In particular, there is no provision to ensure on-centre positioning of a container with respect to the central axis of the clamp plates. Consequently, a careless or hurried operator can place a container significantly off-centre. Also, there is no provision to ensure symmetrical positioning of two or more containers with respect to the central axis of the clamp plates. Even if positioned perfectly, ostensibly identical containers placed side-by-side on the clamp plates may have significantly different contents and hence weights.

The problem of off-axis loading is particularly acute in gyroscopic mixers in view of the rotational imbalance that results from misalignment between the central longitudinal axis of a container and the secondary axis about which the container rotates. In general, the further the centre of gravity of a container is offset from the primary and/or secondary axes about which the container rotates, the greater the off-balance loading on the motor and on other elements of the drive and clamping systems. Off-axis loading is also a problem in vibrational shakers, although they are less sensitive than gyroscopic mixers to incorrect positioning of containers.

No electronic provisions are commonly available to deal with the problem of off-axis loading in mixing machines. In practice, significant vibration is tolerated even though such vibration may shorten the working life of the machine.

Off-balance loading contributes to accelerated wear of machined components such as gears and shafts, and may damage the container or the mixing machine if the imbalance is great enough. For example, fatigue failure of structural components may become an issue with significant and prolonged vibration. It is also more likely that a container may come loose and be dislodged from between the clamp plates during operation of a mixing machine that vibrates excessively.

Of course, some degree of vibration is inevitable when agitating a sloshing fluid mass in a mixing machine. However, tolerating unnecessarily high levels of vibration may eventually lead to premature failure. This risks expensive and disruptive downtime of the machine while waiting for diagnostic and repair visits and for the supply of replacement parts. This is a disadvantage both for the machine user and for the machine supplier, who has to keep a network of repair technicians on standby to fix possible faults. Importantly, it also does nothing to discourage the poor operator behaviour that underlies and prolongs the problem.

Another problem arises from using containers that are dented or otherwise misshapen or damaged. The wall of such a container could be cracked or weakened and hence be prone to leakage or failure under the high stresses and dynamic fluid pressures experienced during clamping and agitation. Such defects also modify the dimensions of the container and may affect its squareness and balance, making it more difficult to clamp the container effectively and more likely that the container will cause excessive vibration even if it is positioned on-centre. A careless or hurried operator may not notice such defects before loading the container into the machine. It is against this background that the present invention has been devised. In one sense, the invention provides a method of monitoring the performance of a mixing machine. Broadly, the method comprises: driving a motor of the mixing machine in accordance with a program; monitoring torque applied by the motor while executing the program; and modifying the program in response to the monitored torque.

For example, the program may be a mix program, in which case the motor is a mix motor controlled in accordance with the mix program to agitate a container that contains a fluid body to be mixed. The method may then comprise: monitoring torque applied by the mix motor while agitating the container; and changing a mix speed of the program in response to the monitored torque.

Conveniently, the duration of the mix program may be changed automatically in inverse relationship to a change in the mix speed. When extending the duration of the mix program in accordance with a reduction in the mix speed, an alert may be issued to an operator that the mix program duration is being extended.

Fluctuations in the torque applied by the mix motor may be monitored while agitating the container. For example, it is possible to calculate a standard deviation of population value for those fluctuations before comparing that value with a stored threshold value and then controlling the mix motor in accordance with that comparison.

In general, the mix motor may be controlled by assessing a torque fluctuation signature that is characterised by torque fluctuation frequency, torque fluctuation amplitude and/or torque deviation relative to a mean value. In that case, the torque fluctuation signature may be compared with one or more corresponding parameters stored in memory or a look-up table. The mix motor may then be controlled in accordance with that comparison.

For example, comparing the torque fluctuation amplitude with a stored threshold value may be used to assess the mass of the fluid body within the container. Or, comparing the torque deviation relative to a mean value with changing orientation of the container during agitation may be used to assess the viscosity of the fluid body within the container. It is also possible to detect the presence of two or more containers being agitated simultaneously by comparing the torque fluctuation frequency with an agitation frequency. Another possible approach is to monitor a level of torque applied by the mix motor while agitating the container to assess the mass of the fluid body within the container. For example, the level of torque may be monitored while accelerating the agitating container to the mix speed, or when the container is being agitated at the mix speed. Conveniently, a mix program may be selected based upon the spacing between a pair of clamp plates as they clamp the container between them before agitation. The mix program may then be modified in accordance with the monitored torque during agitation. Vibration of the machine may be monitored separately when the container is being agitated. This enables cross-checking between the monitored torque and the monitored vibration of the machine to verify the source and the nature of the vibration.

It is also possible for the program to be a clamp program. In that case, the motor is a clamp motor that is controlled in accordance with the clamp program to move at least one of a pair of clamp plates to clamp, between them, a container that contains a fluid body to be mixed. There may be separate mix and clamp motors, or one motor may perform both functions. The clamp motor may be driven to move at least one of the clamp plates while monitoring a level of moving torque applied by the clamp motor to move the, or each, clamp plate or while the, or each, clamp plate is moving. The moving torque level may be compared with a stored threshold value so that an alert can be issued if the moving torque level exceeds the stored threshold value. Such an alert may indicate a need for lubrication or other service attention, such as dealing with an obstruction that causes jamming.

The level of clamping torque applied by the clamp motor may also be monitored while the container is clamped between the clamp plates. The clamping torque level is compared with a stored threshold clamping value. If the threshold value is exceeded, a check is performed as to whether the clamping torque level is maintained to a sufficient extent for a predetermined period of time. If the clamping torque level is not maintained to that sufficient extent over that period of time, an alert may be issued as this implies that the container is being crushed under the clamping pressure. As further verification, the spacing between the clamp plates may be monitored while monitoring the clamping torque level. This enables the monitored clamping torque to be cross-checked with the monitored spacing between the clamp plates.

A method of monitoring mixing machine performance in accordance with the invention can also be expressed within the inventive concept as a diagnostic method. Thus, at least one motor of the mixing machine may be driven in accordance with a diagnostic program. Torque applied by the, or each, motor may be monitored while executing the diagnostic program, enabling a diagnostic report to be provided in accordance with the monitored torque. For example, to assess friction and freedom of movement, the clamp plates may be driven toward and away from each other while monitoring the level of torque applied by the clamp motor.

Alerts and/or reports issued in accordance with the invention may be displayed or otherwise provided to an operator beside the machine and/or may be transmitted to a remote location via a communications network. Correspondingly, the inventive concept may also be expressed as a mixing machine. A mixing machine of the invention comprises: a clamp mechanism comprising a pair of clamp plates, at least one of the clamp plates being movable to clamp a container between the clamp plates; a clamp drive for driving clamping movement of the, or each, movable clamp plate; and a mix drive for causing the clamp mechanism to agitate a clamped container to mix a fluid body held in that container. The machine further comprises a controller that is configured: to execute a program while monitoring torque applied by at least one motor powering the clamp drive and/or the mix drive; and to modify that program in response to the monitored torque. Conveniently, the controller may be configured to monitor torque with reference to data provided by an inverter, via which inverter the controller controls the, or each, motor.

The program may be a mix program that controls the motor powering the mix drive to agitate the clamped container. In that case, the controller may be configured: to monitor torque applied by that motor while agitating the container at a mix speed; and to change the mix speed in response to the monitored torque. The controller is suitably also configured to change the duration of the mix program in accordance with a change in the mix speed. The machine has a user interface to provide various control inputs and information outputs, one of which may be to issue an alert to an operator that the mix program duration is being extended in accordance with a reduction in the mix speed.

The machine may have a position sensor for determining the orientation of the container during a mix program. This allows the controller to compare a torque fluctuation signal with changing orientation of the container during agitation. The machine may also have a proximity sensor for sensing spacing between the pair of clamp plates. This allows the controller to select a mix program, before agitation, based upon that spacing and to modify the mix program in accordance with the monitored torque during agitation. The machine may also have a vibration sensor such as an accelerometer for sensing vibration of the machine when the container is being agitated. This allows the controller to cross-check the monitored torque with the monitored vibration of the machine.

It is also possible for the program to be a clamp program that controls a motor powering the clamp drive to drive clamping movement of the, or each movable clamp plate. As noted above, different motors may drive the mix drive and the clamp drive or the same motor could power both drives.

The inventive concept also embraces a mixing machine that is programmed to perform and to report upon a self-diagnostic routine. In that case, the controller is configured to execute a diagnostic program while monitoring torque applied by at least one motor powering the clamp drive and/or the mix drive; and to provide a diagnostic report in accordance with the monitored torque. A machine of the invention may include, or be connected for data transmission to, a communications system that can issue alerts and/or reports to a remote location via a communications network.

In summary, therefore, the invention monitors the performance of a mixing machine for mixing paints and other fluid bodies by powering a mix drive and/or a clamp drive in accordance with a program. Torque applied by a motor that powers either of those drives while executing the program is monitored and the program may be modified accordingly. For example, mixing speed and mixing duration may be changed if the level of, or fluctuation of, torque applied by a mix motor suggests that the fluid body has characteristics, such as mass, for which the initially-selected mixing program is inappropriate. Similarly, torque applied by a clamp motor may be monitored to determine maintenance issues and to detect if a container carrying a fluid to be mixed is being crushed under clamping pressure.

Thus, the invention protects a mixing machine such as a gyroscopic mixer or a vibrational shaker from aggressive wear conditions and from abuse, hence allowing the machine to last longer and to be more reliable. To achieve this, the mixing machine anticipates, detects and responds to rotational imbalances that may be induced during operation of the machine. The machine can thereby operate at optimised safe speeds while minimising the length of the mixing cycle, and with a reduced risk of the container coming loose prematurely. There is less need for maintenance, especially remedial maintenance.

An automatic shut-down routine may be triggered if extreme vibration is sensed by monitoring torque or a signal from an accelerometer in the mixing machine. In that case, an alert may be issued to an operator and/or to a remote location. At least, an operator may be warned to shut down the machine in such circumstances.

The system of the invention may use information from an inverter that controls a mix motor and/or a clamp motor. The information may be processed by a central controller that is independent of the inverter. The controller monitors deviations of signals received from the inverter or from other sources. Once such deviations increase beyond a threshold, the controller can reduce the operating speed of the mix motor until the deviations return to an acceptable level.

It may be possible in at least some circumstances for the central controller to take actions based upon monitoring run current drawn by a motor, either instead of or in addition to monitoring torque applied by the motor. For example, it may be appropriate to monitor clamp motor current for a single-speed motor as may be used in the vibrational shaker to be described below. The speed of the motor could be calculated through an encoder, which would reflect any slowing of the motor due to the presence of grit or lack of lubrication. As the clamp motor in that case has a gearbox with a high reduction ratio, variations in motor performance may be determined by monitoring various sources of information, which information may be combined to detect or to verify such variations.

In specific embodiments, the invention resides in a mixing machine that may be a mixer or a shaker. The machine may comprise a rotating or otherwise moving frame, a clamping mechanism, a controller and an inverter connected to a motor. The controller monitors fluctuations of torque readings of the motor via the inverter, and controls the rotational speed of the motor to reduce rotational imbalance to a safe operational loading.

Appropriate clamping pressure may be applied according to the weight of a container, as inferred from the spacing between clamp plates and/or from motor torque required to agitate the container.

An alert may be displayed to a user that the machine has exceeded a threshold and that it has adjusted its rotational speed and/or the mixing period. The machine may select the correct rotational speed of the clamping mechanism and the duration of the mixing period according to the mass of the container being agitated in the mixer. The machine may also be capable of determining the number of containers placed in the machine.

The mixing machine may issue alerts consecutively over a period of time, including an alert that the machine requires intervention. For example, the machine may be able to determine if a leadscrew is inadequately greased and issue an alert for maintenance.

The power consumed by the mix motor or drive motor of a mixing machine is generally proportional to the weight of the container to be mixed. However, the size of the container also has an effect on the power drawn by the motor. A short container with a wide diameter will require power and torque levels of a certain profile, when compared with a tall, narrow container. If the power, torque and current required by the mix motor can be monitored continually, either the number of containers being mixed can be inferred, or it can be determined that the container has been placed off-centre.

An electronic control system monitors the power required and torque applied by the mix motor for the first number of revolutions of a mixing program. By comparing them to predetermined stored profiles, the system determines if the values of power and torque match the expected profile for a container of known height. If the torque required to mix the contents of the container is greater than predetermined levels and/or varies substantially with each rotation, the system can automatically slow the mixing speed to ensure that the machine continues to operate within safe working limits. The adjustment in mixing speed may be proportional to the difference in magnitude between the measured values and the expected range. Similarly, the mix program is lengthened to determine the new required mix time, based on how far out of range the torque value was measured. Thus, the mix time may be lengthened progressively in proportion to the magnitude of off-axis loading of the container. The new mix time may be determined according to a formula or in accordance with a look-up table, which may be determined or populated with reference to empirical data based on experimental measurements.

Thus, the invention provides the ability to infer any off-axis loading conditions and to modify the mix operation to a safe and optimal speed, resulting in a significant reduction in risk to an operator and hence a significantly enhanced safety environment for the operator.

Through the above features, the invention provides the ability to infer the weight of a container of a certain size or the density or viscosity of the contents of a container by determining the height of the container, combined with detections of power or current used by the mix motor and/or torque applied by the mix motor.

The functionality of the invention may be extended from detecting off-centre containers to detecting a kinked or dented single container that has been crushed, for example due to weakness, and therefore is manifesting as an off-centre load or otherwise.

The invention may also provide the ability to detect that the machine has been placed on a non-level floor and that levelling feet or legs of the machine have not been positioned appropriately to level the machine correctly.

The invention may also provide the ability to effect remote diagnostics and repair of a mixing machine by detecting signals such as current used and torque applied by the mix and clamp motors. In this way, the mixing machine can infer if its mechanical parts have not been assembled correctly. For example, its bevel gears may be meshed too tightly, resulting in higher friction and higher motor loading, or a drive belt may be overtightened, which demands a higher run current from the associated motor. Similarly, such information may be used to detect that the machine is not optimally assembled, in which case appropriate alerts may be issued. Such alerts may be issued: to the user to check the mechanical state of the machine; to a service manager to advise that the machine needs attention from a technician; or to the manufacturer to warn that the machine has been manufactured, installed and/or operated in a sub- optimal state.

The ability to detect the above anomalies remotely enables a central customer service centre to perform remote adjustments to enhance safety or to prolong machine life.

Similarly, a maintenance provider can schedule service work before the condition of the machine deteriorates to the extent that a breakage is likely to occur, noting that any such failures may result in significant downtime and potentially lost sales. Also, a repair technician may benefit from remote assistance from a central customer service centre, which may be provided in the form of specific targeted digital content directed to the technician to assist repair.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1 is a front perspective view of a gyroscopic mixer in accordance with the invention, from which some panels and other components have been removed for ease of viewing internal parts; Figure 2 is a rear perspective view of the mixer shown in Figure 1 ;

Figure 3 is a sectional side view of a clamp mechanism of the mixer shown in Figures 1 and 2; Figure 4 is a block diagram that shows the main functional elements of the mixer shown in Figures 1 to 3;

Figure 5 is a front perspective view of a vibrational shaker in accordance with the invention;

Figure 6 is a rear perspective view of the shaker shown in Figure 5; Figure 7 is a block diagram that shows the main functional elements of the shaker shown in Figures 5 and 6;

Figure 8 is a graph that shows torque fluctuations of a mix motor of a gyroscopic mixer over time during a mixing operation, for various offsets of a container with respect to the clamp mechanism;

Figure 9 is a flow diagram that shows how a central controller can choose a mixing program and then adapt the mixing program in accordance with torque fluctuations of a mix motor that indicate imbalance;

Figures 10a, 10b and 10c are graphs that show torque fluctuations of a mix motor of a gyroscopic mixer over time during a mixing operation, respectively showing where a container is perfectly aligned with a secondary axis of the clamp mechanism, where a single container is misaligned with that axis, and where two containers are clamped by the clamp mechanism;

Figure 1 1 is a flow diagram that shows how a central controller can detect and react to simultaneous agitation of two or more containers;

Figure 12 is a flow diagram that shows how a central controller can detect and react to the mass of a container and its contents being agitated;

Figure 13 is a graph that shows how the viscosity of the fluid material being mixed influences fluctuations in the torque applied by a mix motor;

Figure 14 is a flow diagram that shows how a central controller can detect and react to the viscosity of the fluid material in a container being agitated;

Figure 15 is a flow diagram that shows how a central controller can cross-check signals from a vibration sensor with fluctuations in the torque applied by a mix motor;

Figure 16 is a graph that shows how torque applied by a clamp motor over time may be used to distinguish between containers that resist and do not resist crushing under clamping pressure; Figure 17 is a flow diagram that shows how a central controller can detect and react to a container being crushed under clamping pressure;

Figure 18 is a flow diagram that shows how a central controller can detect and react to excessive friction in a clamp mechanism; and

Figure 19 is a flow diagram that shows how a central controller can

diagnostic procedure on a mixing machine of the invention. The following description will start with a description of mixing machines of the invention, specifically examples of a gyroscopic mixer and a vibrational shaker in accordance with the invention. The description will then go on to explain the principles that underlie the invention and ways in which the invention can optimise the performance of such mixing machines.

Referring firstly to Figures 1 to 3 of the drawings, a gyroscopic mixer 10 has a frame 12 that supports a clamp mechanism 14. The clamp mechanism 14 is arranged to clamp a container 16, such as a paint can shown schematically in Figure 3, applying clamping pressure to parallel top and bottom faces of the container 16 positioned between opposed clamp plates 18, 20. Thus, the clamp plates 18, 20 are spaced apart in parallel planes, with variable spacing between them.

The clamp mechanism 14 is shown in Figure 1 in a standby or home position in which the clamp plates 18, 20 lie in respective horizontal planes. Consequently, in this position, an upper clamp plate 18 lies directly above a lower clamp plate 20. The lower clamp plate 20 provides a convenient platform onto which to load a container 16 before the clamp plates 18, 20 are driven toward each other to clamp the container 16 between them. At the end of a mixing cycle, the clamp mechanism 14 returns to the home position before moving the clamp plates 18, 20 apart to release the container 16 for removal from the mixer 10.

To enable these relative movements between the clamp plates 18, 20, the clamp mechanism 14 comprises a threaded shaft, worm drive or spindle that serves as a leadscrew 22. The leadscrew 22 can be turned about its longitudinal axis in either angular direction to drive the clamp plates 18, 20 toward each other or apart as required. For this purpose, the clamp plates 18, 20 are supported by respective arms 24, 26 that are slidably mounted on guides 28 extending parallel to the leadscrew 22 from a hub 30.

Specifically, the leadscrew 22 has opposed male threads at opposite ends, hence a left-hand thread extending from the centre to one end and a right-hand thread extending from the centre to the other end. The arms 24, 26 that support the clamp plates 18, 20 are connected to the respective threads of the leadscrew 22 by complementary left-hand and right-hand bronze nuts 32. Thus, unidirectional angular movement of the leadscrew 22 is converted into opposing linear movement of the arms 24, 26 and hence of the clamp plates 18, 20 along the guides 28 in directions parallel to the leadscrew 22. Reversing the direction of angular movement of the leadscrew 22 reverses the opposing linear movement of the clamp plates 18, 20.

As best appreciated in Figure 3, the leadscrew 22 is turned by a clamp pulley 34. The clamp pulley 34 is fixed to a clamp shaft 36 that terminates in a bevel gear drive 38 to turn the leadscrew 22. The clamp pulley 34 is driven, in turn, by a clamp motor 40 via a V-belt 42 as shown in Figure 2.

Figure 2 also shows that the mixer 10 further comprises a mix motor 44 that turns a drive pulley 46 via a belt drive 48. As again best appreciated in Figure 3, the drive pulley 46 turns concentrically around the clamp shaft 36 that joins the clamp pulley 34 to the leadscrew 22. A hollow drive shaft 50 surrounding the clamp shaft 36 joins the drive pulley 46 to the hub 26 and hence to the guides 28 that support the clamp plates 18, 20 via the arms 24, 26. In this way, the guides 28, the arms 24, 26 and hence the clamp plates 18, 20 can turn around a primary axis 52 that is the common axis of rotation of both the drive shaft 46 and the clamp shaft 32.

The clamp plates 18, 20 are rotatably mounted to the respective arms 24, 26 so as to turn around a common secondary axis 54 that is orthogonal to the primary axis 52. To drive this movement of the clamp plates 18, 20, an auxiliary drive shown in Figure 3 comprises a first auxiliary drive shaft 56 that extends orthogonally to the primary axis 52, generally parallel to the guide 28 that holds the arm 24 supporting the upper clamp plate 18. The first auxiliary drive shaft 56 is coupled to a secondary auxiliary drive shaft 58 that extends along the arm 24 to turn the upper clamp plate 18.

The first and second auxiliary drive shafts 56, 58 are turned by an auxiliary bevel gear drive 60 as a consequence of rotation of the drive shaft 50 and the hub 30 relative to the frame 12 of the mixer 10. This turns the upper clamp plate 18 relative to the associated arm 24 about the secondary axis 54. It will be apparent that when a container 16 is clamped between the clamp plates 18, 20, the lower clamp plate 20 will rotate passively relative to the associated arm 26 in response to the driven rotation of the upper clamp plate 18.

It will be apparent from Figure 3 that the leadscrew 22 extends orthogonally with respect to the primary axis 52 and hence is parallel to the secondary axis 54. The block diagram of the mixer 10 in Figure 4 shows that the clamp motor 40 and the mix motor 44 are controlled and switched by an inverter 62 and by respective contactors 64. The inverter 62 and the contactors 64 operate under the control of a central controller 66 that is powered via a power supply 68. The inverter 62 is suitably a three-phase inverter but other inverter types or other forms of motor control and switching are possible, depending upon the nature of the clamp motor 40 and/or the mix motor 44 and their power requirements.

The inverter 62 has data outputs to report to the central controller 66 on the

performance of the clamp motor 40 and the mix motor 44, as expressed in terms of motor power consumption, motor speed and motor torque. As will be explained later, the central controller 66 can calculate motor torque for both the clamp motor 40 and the mix motor 44 if given motor power consumption and motor speed, for example from the inverter 62. Purely as a non-limiting example, an inverter that is suitable for the purposes of the invention is sold under the brand and model Invertek E3, rated for power of 0.75kW and current of 4.3A.

The block diagram shown in Figure 4 further includes a user interface 70 that interacts with the central controller 66. The user interface 70 comprises user interface features such as a display for status messages or error messages, a start button, a standby button, a stop button and an emergency stop button. The stop button will bring the clamp mechanism 14 back to the home position whereas the emergency stop button will halt the clamp mechanism 14 as quickly as possible regardless of its angular position. After a container 16 is loaded onto the lower clamp plate 20 and an operator presses a start button on the user interface 70, the clamp motor 40 starts to turn in a direction appropriate to raise the lower clamp plate 20 and simultaneously to lower the upper clamp plate 18. This radially-inward converging movement of the clamp plates 18, 20 continues until the upper clamp plate 18 comes into contact with the top of the container 16.

At this point, the clamp plates 18, 20 cannot move further but the clamp motor 40 is still applying torque. As a result, the clamp motor 40 draws more power, which is noted at the inverter 62 by an increase in current drawn by the clamp motor 40. The central controller 66 is programmed to respond to such an increase in current, when observed over a certain limit for a specific period of time, by inferring that the container 16 has been clamped. When the container 16 is deemed to be clamped, a proximity sensor 72 determines the spacing between the clamp plates 18, 20. The proximity sensor 72 suitably monitors the location of the clamp plates 18, 20 relative to each other by counting the revolutions of the clamp pulley 34 and hence of the leadscrew 22 that is coupled to the clamp pulley 34 via the clamp shaft 36.

The central controller 66 infers the height of the container 16 from the spacing between the clamp plates 18, 20 and so estimates the overall size and hence the weight of the container 16. The central controller 66 then selects a suitable mixing program for a container 16 of that estimated weight, in terms of mixing speed and mixing duration.

The central controller 66 then initiates the mixing process by controlling the inverter 62 to start the mix motor 44. The inverter 62 is then controlled by the central controller 66 to turn the clamp mechanism 14 around the primary axis 52 at a speed in accordance with the selected program. Simultaneously the clamp plates 18, 20 turn with respect to the remainder of the clamp mechanism 14 around the secondary axis 54. This biaxial rotation tumbles the container 16 and mixes its contents effectively. Meanwhile the clamp motor 40 continues to exert radially-inward clamping pressure on the container 16 via the clamp plates 18, 20. At the end of the mixing program, the central controller 66 slows the mix motor 44 to bring the clamp mechanism 14 to a halt. A position sensor 74 determines the angular position of the clamp mechanism 14 within the mixer 10 to ensure that the mix motor 44 stops with the clamp mechanism 14 stationary at the home position.

With the clamp mechanism 14 now held at the home position, the clamp motor 40 is reversed to move the clamp plates 18, 20 radially apart and hence to release clamping pressure on the container 16. The container 16 now rests once again on the lower clamp plate 20, ready to be removed from the mixer 10.

The block diagram of Figure 4 also shows an optional vibration sensor 76, which may for example be implemented by an accelerometer. The vibration sensor 76 is suitably mounted on the frame 12 of the mixer 10. This provides to the central controller 66 information concerning how the frame 12 is responding to excitation as the clamp mechanism 14 moves to tumble a clamped container 16. Moving on now to Figures 5 to 7 of the drawings, these illustrate a vibrational shaker 78 as another example of a mixing machine in accordance with the invention. For ease of understanding, like numerals are used for features that are broadly equivalent to those of the gyroscopic mixer 10 described above. To avoid repetition, features that have been described above will only be described again to the extent that there is a notable difference between these embodiments.

The shaker 78 comprises a frame 12 and a sprung chassis 80 supported by the frame 12. In turn, the chassis 80 supports a clamp mechanism 14 for clamping a container (not shown), which is shaken during a mixing cycle by shaking the chassis 80 relative to the frame 12. To this end, the chassis 80 carries a mix motor 44 that rotates an eccentric drive shaft 82 to impart out-of-balance oscillatory or vibratory force impulses to the chassis 80.

Again, an inverter 62 controls the rotational speed of the mix motor 44 under the control of a central controller 66. As before, the inverter 62 reports back to the central controller 66 on operational parameters of the mix motor 44 such as rotational speed and power consumption, from which the torque applied by the mix motor 44 can be inferred as noted above. The chassis 80 also supports a reversible clamp motor 40 that turns a leadscrew 22 of the clamp mechanism 14. The leadscrew 22 acts on an upper clamp plate 18 to move the upper clamp plate 18 downwardly toward a lower clamp plate 20 or upwardly away from the lower clamp plate 20, depending upon the direction in which the clamp motor 40 turns.

A revolution sensor 84 implemented by a pulse encoder mounted on the clamp motor 40 counts the revolutions of the clamp motor 40. A non-excited brake 86 also interacts with the central controller 66 and the clamp motor 40.

The revolution sensor 84 determines the position of the upper clamp plate 18 relative to the chassis 80 when the upper clamp plate 18 encounters the top of a container resting on the lower clamp plate 20. As the height of the lower clamp plate 20 relative to the chassis 80 is fixed, this allows the central controller 66 to determine the height of a container 16 clamped between the upper and lower clamp plates 18, 20. The central controller 66 infers the size and weight of the container 16 from this and selects and applies an appropriate mixing program, in the same way as for the gyroscopic mixer 10 described above. Thus, the function of the revolution sensor 84 equates to that of the proximity sensor 72 of the preceding embodiment.

In this embodiment, the clamp motor 40 is not controlled via the inverter 62 but instead is controlled by the central controller 66 via a dedicated circuit board 88. Conveniently, the circuit board 88 is powered by the same power supply 68 that powers the central controller 66. When the upper clamp plate 18 encounters the top of a container resting on the lower clamp plate 20, the clamp motor 40 will draw extra current. The circuit board 88 reports this to the central controller 66. When the current remains over a certain threshold for a certain period of time, the central controller 66 infers that the container is clamped and so starts the appropriate mixing program.

The mixing program continues at an appropriate mixing speed and for an appropriate mixing duration and then is brought to an end by stopping the mix motor 44 so that the chassis 80 stops shaking. Finally the upper clamp plate 18 is raised to allow the container to be lifted from the lower clamp plate 20 and removed from the shaker 78.

Other forms of control and switching are possible, depending upon the nature of the clamp motor 40 and/or the mix motor 44 and their power requirements. For example, both the clamp motor 40 and the mix motor 44 could be controlled by a common inverter 62 as in the preceding embodiment. Having exemplified two mixing machines 10, 78 of the invention above, the principles that underlie the invention will now be explained.

With a suitably short sampling period, the central controller 66 repeatedly records and monitors the torque applied by the mix motor 44 while executing a mixing program. As noted above, motor torque data may be provided from a source such as the inverter 62. Alternatively the central controller 66 can calculate motor torque from the following simplified formula, if provided with motor power consumption data and motor speed data from a source such as the inverter 62:

M_r= {9550P_r)/n_r where M_r is motor torque in Nm; P_r is motor power in kW and n_r is motor speed in rpm. If the mixing machine is in perfectly-balanced operation, the readings of torque applied by the mix motor 44 will be of a constant value. It has been found that the larger the off- balance loadings induced in the machine, the more these measured torque values will become offset from a mean value. To monitor fluctuations of the torque readings of the mix motor 44 from the mean value, the following formula for standard deviation of population may be applied:

— I

Ι H where x is a sample, μ is the population sample average (number-! , number2,...) and n is the number of samples in the population.

As the measured torque readings of the mix motor 44 start to spread out away from the mean value, the larger this standard deviation of population value becomes.

Consequently, the standard deviation of population value can be used to define the response of a mixing machine to increasing off-centre mass by measuring fluctuations of the torque readings of the mix motor 44, as provided by the inverter 62 or as calculated by the central controller 66. By applying this principle to measuring fluctuations in the torque applied by the mix motor 44, the central controller 66 can monitor the effect of changing the position of the container 16 with respect to the clamp plates 18, 20 of a mixing machine. For example, in a gyroscopic mixer 10, the central controller 66 is able to monitor and detect a gradual increase of the imbalance loading as the central axis of the container 16 is moved further away from the secondary axis 54 defined by the clamp mechanism 14.

As an example of how this principle may be applied, Table 1 below shows how the standard deviation of population for measured torque values of the mix motor 44 responds to varying the offset of a container 16 from the secondary axis 54 of a gyroscopic mixer 10. Correspondingly, Figure 8 shows the torque fluctuations over time for the various offsets set out in Table 1.

In each case, the same container 16 of a given weight was used and the mixer 10 was set to turn the container 16 at the same speed.

Table 1: effect of offset at given mixing speed Table 1 and Figure 8 show that there is some minor fluctuation in the torque applied by the mix motor 44 even where the container 16 is centred on the secondary axis 54. This reflects that balance and other variables will always be imperfect in the real world. More significantly, it will be apparent from Table 1 that the standard deviation of population increases markedly as the central axis of the container 16 is moved from alignment with the secondary axis 54 to various increasing degrees of offset from the secondary axis 54. This provides a sensitive measure of increasing rotational imbalance.

As another example of how the principle of the invention may be applied, Table 2 below shows how the standard deviation of population for measured torque values of the mix motor 44 responds to varying the rotational speed of the clamp mechanism 14 of a gyroscopic mixer 10. This is while the same container 16 is at the same position, offset by a few millimetres from the secondary axis 54.

Table 2: effect of mixing speed at given offset

Table 2 demonstrates that controlling the rotational speed of the clamp mechanism 14 in response to fluctuations in the torque applied by the mix motor 44 has a direct and significant effect upon rotational imbalance in the mixer 10.

Figure 9 shows how a mixing machine 10, 78 of the invention can detect and react to imbalance by monitoring torque applied by the mix motor 44 while executing a mixing program. The mixing program is initiated at 90 to set the mixing speed, mixing acceleration and mixing deceleration. In practice, the mixing speed may be varied between predetermined levels during the program to ensure thorough mixing. The mix motor 44 and the associated contactor 64 are enabled at 92 and an appropriate mixing speed is set at 94 while monitoring torque applied by the mix motor 44 at 96.

If torque readings are determined to be within a desired threshold at 98, the mixing program does not need to be adjusted and so is allowed to continue as initially programmed. For this purpose, a process timeout check at 100 determines whether the mixing program has run its course. If the end of the mixing program is determined at 102, a subprocess is initiated at 104 to return the machine 10, 78 to a home or standby state. However if the mixing program is determined at 102 to be continuing, a speed timeout check at 106 determines whether the mixing program should continue at a particular speed level. If the end of a period at a given speed level is determined at 108, the mixing speed is changed accordingly at 94.

Otherwise the mixing speed is unchanged unless torque readings are determined to be outside a desired threshold at 98. In that case, an alert is generated at 1 10 to be displayed on the user interface 70, to the effect that an off-centre can has been detected and that the settings of the mixing program are being adjusted to protect the machine 10, 78. The central controller 66 reacts at 1 12 by reducing the speed of the mix motor 44 until vibration subsides to an acceptable level, as inferred from reduced fluctuation in the torque applied by the mix motor 44. However, as the duration of a mixing program is chosen to ensure complete mixing at the mixing speed associated with that program, the central controller 66 will also prolong a mixing program to compensate for the reduced mixing speed. The central controller 66 may consult a look-up table to select an appropriately longer mixing duration to match the reduced mixing speed.

So, advantageously, the invention allows for vibration of a mixing machine 10, 78 to be controlled while still allowing a mixing program to run its course. This is less disruptive than simply stopping the machine 10, 78 in the event that excessive vibration is detected. However if the central controller 66 determines that there is extreme vibration that cannot be controlled to a reasonable level with a reasonable mixing speed and mixing duration, an operator may be warned to stop the machine or the machine can stop itself automatically. For example, if a container 16 is placed so far off centre that the machine is likely to be damaged, the machine may be programmed to stop mixing entirely, return to the home position and display an alert on the user interface 70 indicating that mixing has been stopped due to the extent of axial mis-alignment of the container 16. The operator may be invited to place the container 16 in the centre of the lower clamp plate 20 and then to press the start button again.

A challenge that arises from protecting a mixing machine 10, 78 from poor operator behaviour - especially by allowing the machine 10, 78 to keep running nevertheless - is that it may not encourage better operator behaviour. Advantageously, therefore, the invention accompanies a reduction in the mixing speed with a warning on the user interface 70 that a longer mixing duration has been applied in view of whatever problem has been detected, whether that problem is incorrect positioning of a container 16 or the simultaneous mixing of multiple containers 16 as the case may be. By experiencing delay as a result, operators are encouraged to improve their behaviour when operating the machine 10, 78 in the future. In particular, by placing containers 16 in the clamp mechanism 14 with greater care, operators benefit from faster mixing programs and the machine benefits from less vibration and hence greater reliability in the long term. Using torque levels to confirm mass can be particularly useful where two or more containers are being mixed side by side, in which case relying upon the height of the containers will give a misleading underestimate of the actual aggregate mass of those containers. Knowing the height of the containers and their apparent aggregate mass also makes it possible to infer how many containers are present, on the basis of assuming the likely weight of a standard-sized container of known height.

Turning next, then, to Figures 10a, 10b and 10c, these graphs show how fluctuations in torque applied by the mix motor during a mixing operation can also be used to determine the number of containers that are clamped by the clamp mechanism.

Figure 10a shows the theoretical situation where a single container 16 is located in its optimal position, for example perfectly aligned with a secondary axis 54 of the clamp mechanism 14 in a gyroscopic mixer 10. In that perfect situation, the mix motor 44 will apply constant torque during the mixing operation, meaning that the torque reading over a period of time is a flat line as shown.

This theoretical example assumes that the container 16 will behave as a solid, rigid body as it is tumbled by the clamp mechanism 14. In practice, the container 16 will not behave in such a perfect way because it contains a fluid mass that has space to move or slosh within the container 16.

Figure 10b shows the theoretical situation where a container 16 is instead located at a non-optimal position within the clamp mechanism 14, for example offset from the secondary axis 54 of a gyroscopic mixer 10. In that case, the torque applied by the mix motor 44 will fluctuate at a particular frequency that is proportional to the mixing speed.

Figure 10c shows the theoretical situation where two containers 16 are positioned side- by-side between the clamp plates 18, 20 of the clamp mechanism 14. In that case, the torque applied by the mix motor 44 will fluctuate at a frequency that is double that expected from the mixing speed. Hence, knowing the mixing speed and the frequency of the fluctuating torque, the central controller 66 can infer not only that there is more than one container 16 in the clamp mechanism 14 but also how many containers 16 are in the clamp mechanism 14.

In practice, the fluctuating torque signals may be considerably noisier than are shown in these theoretical graphs, due to factors such as sloshing contents of the containers 16 and individual offsets of multiple containers 16 from their optimal positions. Signal processing using a fast Fourier transform (FFT) may be applied to process the noisy signal and to determine the rate and amplitude of the imbalance. The central controller 66 may then take appropriate corrective action on that basis.

Figure 1 1 is a counterpart of Figure 9, which shows how a system of the invention may detect multiple containers 16 such as paint cans and modify the mix program accordingly. Features in common with Figure 9 are numbered accordingly and need no further explanation.

In Figure 1 1 , on a first speed setting selected at 1 14, torque fluctuations of the mix motor 44 are processed at 1 16 and interpreted at 1 18 to determine whether there are multiple cans. If multiple cans are not detected, no action is needed. If multiple cans are detected, the mixing speed is reduced and the mixing program time is increased at 1 12. Also, an alert is issued at 120 on the user interface 70.

The aforementioned optional vibration sensor 76 shown in Figures 4 and 7 may also provide information to the central controller 66 regarding how the frame 12 is vibrating or oscillating during a mixing cycle. The central controller 66 can use that information to verify or cross-check information derived from fluctuations in torque applied by the mix motor 44. For example, a signal from a vibration sensor 76 could be used by the central controller 66 when processing at 1 16 to resolve any ambiguity in a complex or noisy torque signal and hence to interpret the torque signal correctly. It may even be possible for the central controller 66 to use a signal from a vibration sensor 76 to determine imbalance or a multiple container scenario without reference to the torque applied by the mix motor 44. More generally, signal input from the vibration sensor 76 could be used in various applications of the invention and not just in the arrangement shown in Figure 1 1 . Thus, by monitoring torque applied by the mix motor 44 throughout a mixing operation as shown in Figures 9 and 1 1 or otherwise by sensing vibration, the central controller 66 continuously monitors the development of vibration that may be induced in a mixing machine. The central controller 66 can then automatically reduce the mixing speed of the clamp mechanism 14 to bring vibration to an acceptable level.

Also, by using torque levels to estimate or corroborate the mass of one or more containers and/or the number of containers, the central controller 66 can choose, or change to, a mixing program that best suits that situation and so is less likely to give rise to vibration.

The mix motor 44 must apply a particular level of torque to move a container 16 of a particular mass. This is not just to accelerate the container 16 up to a desired mixing speed but also, having regard to sloshing or other motion of the fluid mass within, to keep the container 16 moving at that mixing speed. The central controller 66 can correlate the height of the container 16 and the torque required to accelerate the container 16 and/or to keep the container 16 moving to determine the mass of the container 16, and can select or modify the mixing program accordingly.

Thus, a machine 10, 78 of the invention can use the height of a container 16, the level of torque required to accelerate the container 16 and/or to keep the container 16 in a constant state of movement, and other information from the inverter 62, to determine the mass of the container 16.

The central controller 66 is preprogramed to adopt mixing speeds in accordance with the height of a container 16. However, containers can come in many shapes and sizes. Two different containers of the same height but different widths may require agitation for different lengths of time to mix their contents fully. By optimising the mixing profile to suit the nature and volume of the contents of the container 16, the mixing time can be minimised and tailored to the container 16 in question. This reduces unnecessary over- usage of the machine 10, 78, improving reliability while saving time and energy. Either as the machine 10, 78 is accelerating from rest to a first defined speed, or during a first defined time period, the central controller 66 will monitor the torque applied by the mix motor 44 to tumble or otherwise agitate a container 16 at that particular speed. Through testing, a predefined torque requirement may be set for every height of container 16, to determine the weight and optimum mixing speed in each case. The system will store predefined values in a look-up table as a grid that cross-references speed vs height. If the torque applied by the mix motor 44 is below a threshold predicted for a container 16 of a particular height, the container 16 is determined to be of a smaller than predicted mass and therefore will require less mixing time to mix its contents. If the torque applied by the mix motor 44 is above that threshold, the container 16 is determined to be of larger than predicted mass and therefore will require more mixing time to mix its contents. To illustrate this principle, Figure 12 is a further counterpart of Figures 9 and 1 1 , which shows how a system of the invention may determine the mass of one or more containers 16 and modify the mix program accordingly. Again, features in common with Figures 9 and 1 1 are numbered accordingly and need no further explanation.

In Figure 12, on a first speed setting selected at 1 14, mean torque readings are checked at 122 and interpreted at 124 to determine whether the torque applied by the mix motor 44 is above or below a threshold expected for a container 16 of a given height, as determined by the spacing between the clamp plates 18, 20 . If torque is above the threshold, this indicates that the container 16 is larger than expected from its height and so will need a longer mixing program to ensure thorough mixing. The duration of the mixing program is extended accordingly at 126. Conversely, if torque is below the threshold, this indicates that the container 16 is smaller than expected from its height and so thorough mixing can be achieved with a shorter mixing program. In that case, the duration of the mixing program is shortened accordingly at 128.

Optionally, the clamping force applied by the clamp motor 40 may be increased to suit the weight of a heavy container. When a mixing machine 10, 78 agitates a container 16, the fluid contents of the container 16 shift or slosh from side-to-side and/or end-to-end within the container 16. There is a correlation between the viscosity of the material being mixed and the speed of movement of those contents within and relative to the container 16. Thus, another factor that strongly influences the appropriate mixing time is the viscosity of the fluid material being mixed. For example, a watery fluid is of low viscosity and so will require a shorter mixing time than much more viscous materials such as printing inks.

Figure 13 illustrates how the viscosity of the material being mixed has an influence on torque applied by a mix motor 44 of a gyroscopic mixing machine 10. The vertical axis shows torque deviation relative to a mean value. The horizontal axis shows the angle of the container 16 relative to an upright orientation as it completes a full inversion cycle and returns to the upright. In principle, a less viscous material, Product A, will display a smaller amplitude of torque deviation than a more viscous material, Product B. Put another way, the rate of change of torque deviation is greater for the more viscous material and lower for the less viscous material, as indicated by the relative steepness of the curves in Figure 13. The central controller 66 may compare the fluctuating torque readings to values that may be stored in a look-up table populated with the results of previous tests conducted for various materials types. In this way, the central controller 66 may look for a torque fluctuation signature to match that of a known material and thereby deduce the viscosity of the material being mixed, having regard to the mass and size of the container as determined above.. The correct mixing time and/or mixing speed may then be set for that particular material.

In this respect, Figure 14 is a further counterpart of Figures 9, 1 1 and 12, which shows how a system of the invention may determine the viscosity of the contents of a container 16 and modify the mix program accordingly. Again, features in common with Figures 9, 1 1 and 12 are numbered accordingly and need no further explanation.

In Figure 14, on a first speed setting selected at 94, readings for the mean torque applied by the mix motor 44 are checked at 122. Then, deviations and/or the rate of change of torque values are evaluated at 130, leading to a decision to adjust the mixing program at 132, if necessary, in accordance with the behaviour of the material being mixed. In particular, the mix speed setting may be changed at 94 and/or the process timeout may be adjusted at 100 to lengthen or shorten the mixing program to ensure thorough mixing.

Advantageously, the clamp mechanism 14 can always be driven by the mix motor 44 at the highest possible mixing speed that is consistent with maintaining vibration at an acceptable level. Thus, the central controller 66 firstly assumes that a single container has been placed correctly in the clamp mechanism 14 and is of the weight inferred from the height of the container, as assumed from the spacing between the clamp plates 18, 20. The central controller 66 then selects and initiates a suitable mixing program for a single container of that estimated weight, aiming for the fastest mixing speed and mixing duration deemed possible for that assumed situation.

If the level of torque applied by the mix motor at the start of the mixing operation is significantly higher than expected, this indicates that the weight of the container is significantly greater than the spacing between the clamp plates would suggest. For example, there may be multiple containers positioned side-by-side, or a container may be filled with an unusually dense or viscous fluid, or a container may be unusually wide for its height. In that case, the central controller 66 can choose a more appropriate mixing program or can modify the program that was already selected. If it transpires during the mixing operation that the container is off-centre or is even heavier than expected, this will manifest itself as unexpected vibration at the chosen mixing speed. If the container contains an unusually viscous fluid, this may also increase vibration unexpectedly. Significantly increased vibration may also arise if there are in fact two or more containers between the clamp plates 18, 20, which multiplies the weight expected of a single container and increases the likelihood of unbalanced positioning of the containers between the clamp plates 18, 20. As noted above, imbalance will be detected from fluctuation in the torque applied by the mix motor 44. The central controller 66 can then respond appropriately by instructing the inverter 62 to reduce the speed of the mix motor 44.

When a mixing machine 10, 78 is being installed, the installer is responsible to ensure that the machine 10, 78 has been installed correctly. However, in some cases, the installer may not ensure that stabiliser feet under the machine 10, 78 are adjusted correctly to ensure that the machine is level and will not vibrate unduly during normal operation. Unless the feet are correctly adjusted, the machinel O, 76 could rock upon, or even move across, an inclined or uneven floor. Such vibration during normal operation due to an unstable setup could cause unnecessary stress to the mechanics and electronics of the machine 10, 78.

Fluctuations in motor torque that detect imbalance arising from, for example, off-axis positioning of a container 16 may not necessarily detect imbalance arising from the mixing machine 10, 78 being positioned on a floor that is not level or that is uneven. Thus, the optional vibration sensor 76 may be used to detect such a situation and to cause the central controller 66 to generate an appropriate alert. Specifically, during normal operation, the central controller 66 may cross-check vibrations detected through torque fluctuation against vibrations detected by the vibration sensor 76 to determine whether the vibrations are due to internal issues such as container misalignment or instead are due to the machine 10, 78 being installed incorrectly.

In this respect, reference is made to Figure 15 to show how a mixing machine 10, 78 of the invention can distinguish between these different sources of vibration. Here, when mixing operation of the machine 10, 78 is confirmed at 134, fluctuations in torque applied by the mix motor 44 are checked at 136 and signals from the vibration sensor 76 are checked at 138. The signals checked at 136 and 138 are compared at 140 and a significant disparity between them over time causes an appropriate alert to be generated at 142 via the user interface 70.

The inventive concept of monitoring torque applied by the mix motor 44 may also extend to monitoring torque applied by the clamp motor 40. Some examples of this principle will now be described.

As noted above, a spike in current drawn by the clamp motor 40 can be used by the central controller 66 to determine when a container has been clamped. However, the characteristics of that spike may also be analysed to determine the condition of the container, optionally in conjunction with data from the proximity sensor 72.

For example, a strong, rigid container with a top parallel to its base would be expected to stop convergence of the clamp plates 18, 20 suddenly as soon as the upper clamp plate 18 encounters the top of the container. The result will be a sharp spike in current drawn by the clamp motor 40 and in torque applied by the clamp motor 40, in addition to a sudden cessation of movement of the clamp plates 18, 20 that may be detected by the proximity sensor 72. If the container is off-square or has a weakened wall, for example as a result of a dent, convergence of the clamp plates 18, 20 may not stop as suddenly when the upper clamp plate 18 encounters the top of the container. In particular, the clamp plates 18, 20 may continue to converge, at least for a short distance, because a weaker or misaligned container is less able to resist axial compression. The result will be a softer spike in current drawn by the clamp motor 40, or a tailing off of torque applied by the clamp motor 40. Also, the proximity sensor 72 may detect continuing movement of the clamp plates 18, 20 or, at least, less sudden cessation of movement of the clamp plates 18, 20. If an off-square or weakened container is detected in this way, the central controller 66 may issue an error message inviting an operator to check or replace the container before allowing the mixing program to begin.

In this respect, reference is made to Figure 16 of the drawings, which shows the difference in torque applied by the clamp motor 40 over time between clamping a container 16 that resists crushing under clamping pressure and a situation where a container 16 is crushed to some extent under clamping pressure. In both cases, torque applied by the clamp motor 40 increases rapidly when the upper clamp plate 18 encounters the top of the container 16. If the container 16 resists crushing, the torque level remains high, and settles at a substantially constant level slightly below an initial peak. In contrast, if the container 16 starts to collapse, the torque level reduces over time and will continue to tail off unless and until the crushed container 16 is able to resist the clamping pressure. The proximity sensor 72 may also detect continuing movement of the clamp plates 18, 20 after the initial spike in torque level.

Thus, during the clamping process, a mixing machine 10, 78 in accordance with the invention will detect the presence of a container 16 between the clamp plates 18, 20 when the torque applied by the clamp motor 40 increases above a threshold. When this torque value is substantially constant and above a threshold for a predefined time, the central controller 66 can determine when the clamp plates 18, 20 have reached their limit of convergence and that the container 16 is clamped correctly. However, if the torque value starts to decrease, the central controller 66 can infer that the structure of the container 16 is changing and is no longer resisting the clamping pressure being applied to it.

The above crush-detection procedure is exemplified in Figure 17. Here, an initial routine 144 ensures that a door of the machine providing access to the clamp mechanism 14 is correctly closed. Next, the height of the upper clamp plate 18 is checked at 146 and monitored at 148 to determine the spacing between the clamp plates 18, 20. Torque applied by the clamp motor 40 is monitored at 150 and compared with a threshold value at 152. If torque is not over the threshold value and there is no clamping timeout as determined at 154, the clamp motor 40 continues to drive the clamp plates 18, 20 together. If a clamping timeout is determined at 154, the clamping process ends without initiating a mixing process.

If torque over the threshold value is determined at 152, a determination is made at 156 whether the torque level remains substantially constant for a short period of, for example, 1 to 2 seconds. If so, correct clamping is inferred and therefore convergence of the clamping plates 18, 20 is stopped at 158 before the mixing process is run at 160. If not, crushing is inferred, generating an appropriate alert at 162 that may be provided on the user interface 70. In that event, again, the clamping process ends without initiating the mixing process. Monitoring the torque applied by the clamp motor 40 during a clamping operation can also be used to monitor the condition of the clamp mechanism 14. In this respect, the clamp mechanism 14 requires low friction as the clamp plates 18, 20 and their associated structures travels towards or away from a container 16. Friction will increase with poor maintenance and may eventually lead to premature failure.

Table 3 below shows variations in torque applied to the clamp motor 40 under different frictional conditions. In Test 1 , the machine was in optimal factory condition, correctly lubricated. In Test 2, the leadscrew 22 and guides 28 were unlubricated. In Test 3, the leadscrew 22 and guides 28 were unlubricated and also had been run continuously for two days.

Table 3: effect of lubrication on clamp motor torque

It will be apparent from Table 3 that monitoring the torque applied by the clamp motor 40 can be used effectively to monitor the condition of the clamp mechanism 14.

One of the most frequent maintenance requirements in mixing machines 10, 78 like those described above is to ensure that their leadscrews 22 are adequately lubricated to ensure smooth clamping operation and to prevent wear of machined components. If the leadscrew 22 is not lubricated regularly, the clamping operation becomes noisier due to an increase in friction between the leadscrew 22 and the associated nuts 32. As a consequence, the clamp motor 40 must apply more torque to achieve the same movement of the clamp plates 18, 20.

If the power consumed by a clamp motor 40, for a specific machine, is calibrated when the leadscrew 22 is correctly lubricated, it can be inferred that if the clamp motor 40 draws progressively more power over time, then the leadscrew 22 is becoming progressively less lubricated. In other words, the reduction in lubrication leads to an increase in friction, which necessitates increased power and torque to move the nuts 32 along the leadscrew 22. In principle, laboratory tests may be conducted to establish the power required to run the nuts 32 along an unlubricated leadscrew 22. The actual clamping power requirement of a mixing machine 10, 78 can then be compared to this datum level. Over the course of a period of use of, say, a year or two, the power level required to clamp a container 16 may be monitored and compared to the unlubricated datum level. Once the power consumed in a clamping operation approaches that datum level, a software control system can instruct the operator that the mixing machine 10, 78 needs lubrication in order to work effectively, and to prevent unnecessary wear.

In this respect, Figure 18 shows how a machine 10, 78 of the invention can determine and indicate that lubrication is required. When initiating a clamping operation at 164, torque applied by the clamp motor 40 is monitored at 166 as the clamp plates 18, 20 converge. A determination is made at 168 whether the torque value is over a threshold that indicates lubrication is required. If the torque value is not over that threshold, no action follows. If the torque value is over a threshold, an alert is issued at 170. That alert may be presented on the user interface 70. This alert, and all other alerts issued by the machine 10, 78, may also be transmitted to personnel at a remote location such as a service technician based at a customer service centre. Transmission of alerts may, for example, be effected via the cloud.

Similar principles may be applied to the maintenance of the mixing system that is driven by the mix motor 44. In this respect, specific container sizes, sensed by determining the position of the clamp plates 18, 20, will have specific pre-determined ranges of mix torque. Thus, the central controller 66 can identify where the torque applied by the mix motor 44 to a container 16 of known size is outside the normal operating range expected for a container 16 of that size, indicating a need for lubrication. Turning finally to Figure 19 of the drawings, this illustrates a self-diagnosis procedure that can be performed by a mixing machine 10, 78 of the invention. This procedure is intended to improve reliability and to detect mechanical faults by checking if the mechanics of the machine 10, 78 are within acceptable operational limits. The self-diagnosis procedure may be initiated automatically by the machine 10, 78 from time to time, or on request of the operator or of a remote service technician. On initiation, the machine 10, 78 alerts the operator at 172 that self-diagnosis has been activated and at 174 locks a door that controls access to the clamp mechanism 14.

Next, at 176, the clamp mechanism 14 is clamped fully until the clamp plates 18, 20 reach a mechanical limit position of convergence and is then undamped fully until the clamp plates 18, 20 reach a mechanical limit position of divergence. During this operation, the central controller 66 checks that readings of the separation of the clamp plates 18, 20 are correct. The central controller 66 also checks at 178 if the torque applied by the clamp motor 40 is within a predefined threshold in terms of level and fluctuations. This is to ensure that there is adequate lubrication on the leadscrew 22, that there is appropriate belt tension and that friction between components of the clamp mechanism 14 generally is within acceptable limits.

After checking movement of components of the clamp mechanism 14, the central controller 66 checks movement of the entire clamp mechanism 14 itself, such as rotation of the clamp mechanism 14 in a gyroscopic mixer 10. While the clamp mechanism 14 moves as a whole at 180, the central controller 66 monitors the torque applied by the mix motor 44 at 182 to detect resistance and fluctuations due to issues such as ungreased components, friction, jamming or backlash. The central controller 66 can also monitor slight fluctuations due to mechanical damage, such as teeth missing from a gear or the presence of grit between sliding or rotating parts.

After these steps of the self-diagnosis procedure have been completed, the

components of the machine 10, 78 are reset to the home position at 184. The door controlling access to the clamp mechanism is then unlocked to allow for normal operation of the machine 10, 78.

If any maintenance issues are diagnosed, the machine 10, 78 may issue an alert to an operator via the user interface 70 and/or also send a alert to a remote service technician through the cloud. That alert may involve displaying a test report at 186.

With self-sensing features such as these programmed into the control system of a mixing machine, the machine can protect itself from customer misuse to some extent. Thus, the machined components of the machine will wear at a slower rate, delaying or preventing breakage, hence allowing the machine to last longer yet possibly with less maintenance. Additionally, data concerning machine usage information may be communicated back to a database at a central customer service centre, allowing the condition of multiple machines to be monitored continually at a central point. Such data may, for example, be communicated via an Ethernet or Wi-Fi connection and may include information such as the number of mixing cycles, the sizes of cans mixed and the power consumed and torque required by both the mix and clamp motors.

In this way, it is possible to deduce when a machine is being subjected to use conditions that mandate a maintenance intervention so as to prevent the machine from breaking down. This may save huge costs if it avoids a call from a customer service technician, especially if the technician has to travel a significant distance to a remote machine to perform a repair.

The features of the invention allow the operator of a mixing machine to enjoy the benefits of intelligent machine ownership. This results in significant savings arising from the reduced costs associated with automatic machine maintenance.

Claims

1. A method of monitoring mixing machine performance, the method comprising:

driving a motor of the mixing machine in accordance with a program; monitoring torque applied by the motor while executing the program; and modifying the program in response to the monitored torque.

2. The method of Claim 1 , wherein the program is a mix program and the motor is a mix motor controlled in accordance with the mix program to agitate a container that contains a fluid body to be mixed, the method comprising:

monitoring torque applied by the mix motor while agitating the container; and changing a mix speed of the program in response to the monitored torque.

3. The method of Claim 2, comprising changing a duration of the mix program in accordance with a change in the mix speed.

4. The method of Claim 3, comprising:

extending the duration of the mix program in accordance with a reduction in the mix speed; and issuing an alert to an operator that the mix program duration is being extended.

5. The method of any of Claims 2 to 4, comprising monitoring fluctuations of the torque applied by the mix motor while agitating the container.

6. The method of Claim 5, comprising calculating a standard deviation of population value for said fluctuations, comparing said value with a stored threshold value, and controlling the mix motor in accordance with said comparison.

7. The method of Claim 5 or Claim 6, comprising controlling the mix motor by assessing a torque fluctuation signature that is characterised by one or more of the following parameters: torque fluctuation frequency; torque fluctuation amplitude; or torque deviation relative to a mean value.

8. The method of Claim 7, comprising comparing the torque fluctuation signature with one or more corresponding stored parameters and controlling the mix motor in accordance with said comparison.

9. The method of Claim 8, comprising comparing the torque fluctuation amplitude with a stored threshold value to assess the mass of the fluid body within the container.

10. The method of any of Claims 7 to 9, comprising comparing the torque deviation relative to a mean value with changing orientation of the container during agitation to assess viscosity of the fluid body within the container.

1 1. The method of any of Claims 7 to 10, comprising comparing the torque fluctuation frequency with an agitation frequency to detect the presence of two or more containers being agitated simultaneously.

12. The method of any of Claims 2 to 4, comprising monitoring a level of torque applied by the mix motor while agitating the container to assess the mass of the fluid body within the container.

13. The method of Claim 12, comprising monitoring the level of torque while accelerating the agitating container to the mix speed.

14. The method of Claim 12 or Claim 13, comprising monitoring the level of torque when the container is being agitated at the mix speed.

15. The method of any of Claims 2 to 14, comprising selecting a mix program based upon spacing between a pair of clamp plates that clamp the container between them before agitation; and modifying the mix program in accordance with the monitored torque during agitation.

16. The method of any of Claims 2 to 15, further comprising monitoring vibration of the machine when the container is being agitated.

17. The method of Claim 16, comprising cross-checking the monitored torque with the monitored vibration of the machine.

18. The method of Claim 1 , wherein the program is a clamp program and the motor is a clamp motor that is controlled in accordance with the clamp program to move at least one of a pair of clamp plates to clamp, between them, a container that contains a fluid body to be mixed.

19. The method of Claim 18, comprising:

driving the clamp motor to move at least one of the clamp plates; monitoring a level of moving torque applied by the clamp motor to move the, or each, clamp plate or while the, or each, clamp plate is moving; comparing said moving torque level with a stored threshold value; and issuing an alert if said moving torque level exceeds the stored threshold value.

20. The method of Claim 18 or Claim 19, comprising:

monitoring a level of clamping torque applied by the clamp motor while the container is clamped between the clamp plates; comparing said clamping torque level with a stored threshold clamping value; and if the threshold value is exceeded, checking whether the clamping torque level is maintained to a sufficient extent for a predetermined period of time.

21. The method of Claim 20, comprising issuing an alert if the clamping torque level is not maintained to that sufficient extent over said period of time.

22. The method of Claim 21 or Claim 22, further comprising monitoring spacing between the clamp plates while monitoring the clamping torque level.

23. The method of Claim 22, comprising cross-checking the monitored clamping torque with the monitored spacing between the clamp plates.

24. A method of monitoring mixing machine performance, the method comprising:

driving at least one motor of the mixing machine in accordance with a diagnostic program; monitoring torque applied by the, or each, motor while executing the diagnostic program; and providing a diagnostic report in accordance with the monitored torque.

25. The method of Claim 24, comprising:

driving a clamp motor to move at least one of a pair of clamp plates; and monitoring a level of torque applied by the clamp motor to move the, or each, clamp plate or while the, or each, clamp plate is moving.

26. The method of Claim 25, comprising reducing and increasing relative separation between the clamp plates while monitoring the level of torque applied by the clamp motor.

27. The method of any of Claims 24 to 26, comprising:

driving a mix motor to cause a clamp mechanism of the machine to agitate; and monitoring torque applied by the mix motor while the clamp mechanism is agitating.

28. The method of Claim 27, comprising monitoring fluctuations of the torque applied by the mix motor while the clamp mechanism is agitating.

29. The method of Claim 27 or Claim 28, comprising monitoring the level of torque applied by the mix motor while the clamp mechanism is agitating.

30. The method of any preceding claim, comprising initiating an emergency shut-down routine upon detecting unsafe or damaging operation.

31 . The method of any preceding claim, comprising issuing alerts and/or reports to a remote location via a communications network.

32. A mixing machine, comprising:

a clamp mechanism comprising a pair of clamp plates, at least one of the clamp plates being movable to clamp a container between the clamp plates; a clamp drive for driving clamping movement of the, or each, movable clamp plate; and a mix drive for causing the clamp mechanism to agitate a clamped container to mix a fluid body held in that container; wherein the mixing machine further comprises a controller that is configured: to execute a program while monitoring torque applied by at least one motor powering the clamp drive and/or the mix drive; and to modify that program in response to the monitored torque.

33. The machine of Claim 32, wherein the controller is configured to monitor torque with reference to data provided by an inverter, via which inverter the controller controls the, or each, motor.

34. The machine of Claim 32 or Claim 33, wherein the program is a mix program that controls the motor powering the mix drive to agitate the clamped container, and the controller is configured: to monitor torque applied by that motor while agitating the container at a mix speed; and to change the mix speed in response to the monitored torque.

35. The machine of Claim 34, wherein the controller is configured to change the duration of the mix program in accordance with a change in the mix speed.

36. The machine of Claim 35, further comprising a user interface through which the controller can issue an alert to an operator that the mix program duration is being extended in accordance with a reduction in the mix speed.

37. The machine of any of Claims 34 to 36, wherein the controller is configured to monitor fluctuations of the torque applied by said motor while agitating the container.

38. The machine of Claim 37, wherein the controller is configured: to calculate a standard deviation of population value for said fluctuations; to compare said value with a threshold value stored in a memory; and to control said motor in accordance with said comparison.

39. The machine of Claim 37 or Claim 38, wherein the controller is configured to control said motor by assessing a torque fluctuation signature that is characterised by one or more of the following parameters: torque fluctuation frequency; torque fluctuation amplitude; or torque deviation relative to a mean value.

40. The machine of Claim 39, wherein the controller is configured: to compare the torque fluctuation signature with one or more corresponding parameters stored in the memory; and to control said motor in accordance with said comparison.

41 . The machine of Claim 40, wherein the controller is configured to compare the torque fluctuation amplitude with a threshold value stored in the memory.

42. The machine of any of Claims 39 to 41 , wherein the controller is responsive to a sensor for determining orientation of the container and is configured to compare the torque deviation relative to a mean value with changing orientation of the container during agitation.

43. The machine of any of Claims 39 to 42, wherein the controller is configured to compare the torque fluctuation frequency with an agitation frequency of the clamp mechanism.

44. The machine of any of Claims 34 to 36, wherein the controller is configured to monitor a level of torque applied by said motor while agitating the container.

45. The machine of Claim 44, wherein the controller is configured to monitor the level of torque applied by said motor while accelerating the agitating container to the mix speed.

46. The machine of Claim 44 or Claim 45, wherein the controller is configured to monitor the level of torque applied by said motor when the container is being agitated at the mix speed.

47. The machine of any of Claims 34 to 46, wherein the controller is responsive to a sensor for sensing spacing between the pair of clamp plates and is configured to select a mix program based upon that spacing before agitation and to modify the mix program in accordance with the monitored torque during agitation.

48. The machine of any of Claims 34 to 47, wherein the controller is responsive to a sensor for sensing vibration of the machine when the container is being agitated.

49. The machine of Claim 48, wherein the controller is configured to cross-check the monitored torque with the monitored vibration of the machine.

50. The machine of Claim 32 or Claim 33, wherein the program is a clamp program that controls a motor powering the clamp drive to drive clamping movement of the, or each movable clamp plate.

51 . The machine of Claim 50, wherein the controller is configured: to monitor a level of torque applied by said motor to move the, or each, clamp plate or while the, or each, clamp plate is moving; to compare the torque level with a threshold value stored in a memory; and to issue an alert if the torque level exceeds the stored threshold value.

52. The machine of Claim 50 or Claim 51 , wherein the controller is configured: to monitor a level of torque applied by said motor while the container is clamped between the clamp plates; to compare the torque level with a threshold clamping value stored in a memory; and if the threshold value is exceeded, to check whether the torque level is maintained to a sufficient extent for a predetermined period of time.

53. The machine of Claim 52, wherein the controller is configured to issue an alert if the torque level is not maintained to that sufficient extent over said period of time.

54. The machine of Claim 52 or Claim 53, wherein the controller is responsive to a sensor for sensing spacing between the pair of clamp plates and is configured to monitor said spacing while monitoring the torque level.

55. The machine of Claim 54, wherein the controller is configured to cross-check the monitored torque with the monitored spacing between the clamp plates.

56. A mixing machine, comprising:

a clamp mechanism comprising a pair of clamp plates, at least one of the clamp plates being movable to clamp a container between the clamp plates; a clamp drive for driving clamping movement of the, or each, movable clamp plate; and a mix drive for causing the clamp mechanism to agitate a clamped container to mix a fluid body held in that container; wherein the mixing machine further comprises a controller that is configured to execute a diagnostic program while monitoring torque applied by at least one motor powering the clamp drive and/or the mix drive; and to provide a diagnostic report in accordance with the monitored torque.

57. The machine of Claim 56, wherein the controller is configured to monitor torque with reference to data provided by an inverter, via which inverter the controller controls the, or each, motor.

58. The machine of Claim 56 or Claim 57, wherein the controller is configured: to drive a motor that powers the clamp drive to move at least one of the clamp plates; and to monitor a level of torque applied by that motor to move the, or each, clamp plate or while the, or each, clamp plate is moving.

59. The machine of Claim 58, wherein the controller is configured to reduce and increase relative separation between the clamp plates while monitoring the level of torque applied by said motor.

60. The machine of any of Claims 56 to 59, wherein the controller is configured: to drive a motor that powers the mix drive to cause the clamp mechanism to agitate; and to monitor torque applied by that motor while the clamp mechanism is agitating.

61 . The machine of Claim 60, wherein the controller is configured to monitor fluctuations of the torque applied by said motor while the clamp mechanism is agitating.

62. The machine of Claim 60 or Claim 61 , wherein the controller is configured to monitor a level of torque applied by said motor while the clamp mechanism is agitating.

63. The machine of any of Claims 32 to 62, wherein the controller is configured to initiate an emergency shut-down routine upon detecting unsafe or damaging operation

64. The machine of any of Claims 32 to 63, further comprising a communications system that is configured to issue alerts and/or reports to a remote location via a communications network.