Field of the Invention The present invention concerns mattresses and mattress systems. More particularly, but not

exclusively, this invention concerns a mattress system for the reduction of pressure sores. The invention also concerns a mattress system with a control unit.

Background of the Invention

Various mattresses and mattress systems exist which attempt to reduce the occurrence of pressure sores in long term users, such as hospital and care patients.

Pressure sores can develop when a bed user lies in the same position for an extended period of time. Various systems exist depending on the level of risk of

developing pressure sores for a bed user. For example, in a high-risk scenario, an active mattress system may be provided, where an air pump is used to cyclically vary the pressure inside numerous air chambers which make up a mattress .

The level of risk of someone developing pressure sores may be determined by use of a checklist or scale, which may be applied by a care giver to a patient. An example of such a scale is the Waterlow Scale. If a patient is determined to be at high risk of a pressure ulcer, they may be provided with an active mattress system as described above. However, some patients may find it difficult to sleep on an active mattress system, with the resulting sleep deprivation causing alternative health problems. There may also be patients which are at a boundary on the risk scale, where it is difficult to know whether an active mattress system should be used.

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved mattress system.

Summary of the Invention The present invention provides, according to a first aspect, a mattress system comprising:

a mattress comprising a plurality of interconnected chambers ;

a control unit;

the interconnected chambers connected to the control unit, whereby activation of the control unit may increase or decrease the pressure within the interconnected chambers ;

the control unit comprising one or more sensors arranged to detect pressure changes in the plurality of interconnected chambers, wherein the mattress system is configured for use in an active mode, where the control unit is activated to increase or decrease the pressure within the interconnected chambers, and a passive mode where the control unit is arranged to monitor the

pressure changes in the plurality of interconnected chambers, wherein the control unit is arranged to be configured in the active mode or passive mode based on the pressure changes detected by the one or more sensors.

The mattress system may further comprise a

calibration mode, wherein the control unit is arranged to increase the pressure within the plurality of

interconnected chambers to a first pressure, then allow the deflation of the plurality of interconnected chambers to a second pressure, whereby the time taken to deflate from the first pressure to the second pressure is

monitored and recorded. The time taken to deflate from the first pressure to the second pressure, which may from herein be referred to as the "deflation time" may

indicate the approximate weight of a patient lying on the bed. For example, a heavier patient may have a shorter deflation time than a lighter patient. The control unit may have a memory unit including a correlation between the deflation time and the approximate weight of a patient. The control unit may be adjustable in

dependence on the detected deflation time as will be set out in more detail below.

The control unit may comprise a pump unit or

compressor unit. The pump unit or compressor unit may be controlled by the control unit to increase or decrease the pressure within the interconnected chambers when the control unit is in the active mode.

The control unit may be arranged to monitor the pressure changes detected by the one or more sensors. The control unit may comprise a communications module. The communications module may be controlled by the control unit. The communications module may be arranged to send communications signals via wired or wireless communication channels. For example, the communications module may be arranged to send communications signals to a mobile phone device, or a remote monitoring call centre. The communications module may be arranged to receive communications signals via wired or wireless communication channels. The communications signals may include alert signals. The communications signals may include control signals, for example control signals which activate or deactivate the active mode of the control unit. The control signals may include one or more activation sequences, for example relating to the duration or activation frequency of the active mode of the control unit.

The control unit may comprise a processor, the processor arranged to analyse the pressure changes detected by the one or more sensors of the control unit. The processor may, in response to a first set of pressure changes, send a first signal from the control unit. The processor may, in response to a second set of pressure changes, send a second signal from the control unit.

The first set of pressure changes may be chosen such that they indicate the patient is moving frequently enough, and in an appropriate manner, such that pressure ulcers are unlikely. The first set of pressure changes may comprise a threshold pressure change, above which the movement of a patient is taken to be a useful movement, for example a rotational movement of the torso of a patient. Pressure changes below the threshold pressure change may be taken to be non-useful movement, for example an arm movement of the patient. An example threshold pressure change may be between 0.5mmHg and lOmmHg, or between lmmHg and 5mmHg. The threshold pressure change may be 2mmHg. The threshold pressure change may be adjusted in dependence on the weight of the patient, for example the weight as detected by the use of the calibration mode of the mattress system. The first set of pressure changes may comprise between 1 and 10, or between 1 and 5, or for example 3, pressure changes above the threshold pressure in an hour long period.

The second set of pressure changes may be chosen such that they indicate the patient is not moving frequently enough, or in an appropriate matter, thereby indicating the risk of pressure ulcers is high. An example of inappropriate (non-useful) movement would be where the patient is only moving their arms; as this movement may be insufficient to prevent pressure ulcer development on their torso. The second set of pressure changes may comprise detection of little or no pressure changes over a set period of time. The second set of pressure changes may comprise detection of an

insufficient number of pressure changes which exceed the threshold pressure change in a given time period. The insufficient number may be zero, one or two threshold pressure changes an hour, for example.

In response to the first signal sent from the processing unit, the control unit may be arranged to enter, or remain in, the passive mode. In response to the first signal, the control unit may be arranged such that the communications module sends an "OK" signal to a remote monitor, for example the phone of a nurse or a call centre.

In response to the second signal sent from the processing unit, the control unit may be arranged enter the active mode. The control unit may be arranged to enter the active mode automatically. Such an arrangement may be advantageous both in remote care scenarios, and in busy hospital environments. The risk of pressure ulcers developing may be reduced without requiring any input from a care provider.

In response to the second signal sent from the processing unit, the control unit may be arranged such that the communications module sends an alert signal to a remote monitor. The remote monitor may then send an activation signal which is received by the communications module, whereupon the active mode is activated. Such an arrangement may be advantageous in a home care

environment, where a patient is not in regular contact with a care provider. The movement patterns of the patient may be monitored such that in the event of a risk of pressure ulcers developing, the active function of the mattress system may be activated remotely.

The control unit may comprise an alarm. The alarm may be an audible and/or visual alarm. The alarm may be arranged to be activated in response to the second signal being sent by the processing unit. The control unit may comprise a display screen, and the visual alarm may be shown on the display screen. Such an arrangement may be advantageous in a noisy and busy hospital environment, making it clear to a care provider that the patient is at risk of developing pressure ulcers.

Depending on the particular circumstances in which the mattress system is used, it may be preferable to require a care provider to choose whether or not the active mode of the control unit is activated. For example, the care provider may decide that leaving the control unit in the passive mode would result in better sleep for the patient, with the benefit of sleep

outweighing the risk of pressure ulcers developing.

The control unit may comprise an input and an output, the input and output connected to the plurality of interconnected chambers. The input may be arranged to reduce pressure within the plurality of interconnected chambers. The output may be arranged to increase

pressure within the plurality of interconnected chambers. The input and output may be a single physical connection to the control unit, and switch between being an input and output based on the operation of the control unit. The mattress system may comprise a first set of interconnected chambers and a second set of

interconnected chambers. The first set of interconnected chambers may be independent of the second set of

interconnected chambers. In one embodiment, the first set of interconnected chambers may be independent of the second set of interconnected chambers when in the active mode, and the first set of interconnected chambers may be connected to (i.e. allowing fluid communication between) the second set of interconnected chambers when in the passive mode. The change between the independent

operation and connection between the first set of interconnected chambers and second set of interconnected chambers may be controlled by a switch, for example a solenoid switch. The pressure within the first set of interconnected chambers and pressure within the second set of interconnected chambers may be independently controlled by the control unit.

In the active mode, the control unit may, for example, increase the pressure within the first set of interconnected chambers at the same time as decreasing the pressure within the second set of interconnected chambers, or vice versa. The first set of chambers may comprise a plurality of individual air chambers and the second set may comprise a plurality of individual air chambers. The chambers of the first set and the second set may be alternately laid out in the direction of the length of the mattress. The air pressure in the first set and the second set may alternately increase and decrease out of phase with each other; preferably 180 degrees out of phase, such that the pressure in the first set is always being increased as the pressure in the second set is being decreased. In the active mode, the control unit may be arranged to increase and decrease the pressure within the chambers in a cyclical fashion. That is to say, the pressure in each air chamber may be periodically increased and decreased. Air chambers which are in fluid communication, or otherwise are a part of the same set, may increase and decrease in pressure with the same period.

The skilled person will appreciate that there are a number of possible patterns in which the air pressure in the chambers of the mattress may be increased and

decreased. This will depend to some extent on the

capabilities of the control unit and the specific

arrangement of the air chambers. In some embodiments, three or more sets of chambers may be provided. It may also be the case that in the active mode the control unit causes a random inflation and deflation of the air chambers (to the extent that is possible if they are grouped into interconnected sets) such that the overall effect on the patient, in terms of allowing the pressure of the matters on a part of the body not to stay the same for longer than a threshold time, is similar to a regular (non-random) periodic inflation of the air chambers.

At least some of the air chambers may be

substantially elongate. At least some of the air chambers may span more than 50%, 60%, or 70% the width of the bed.

There may be a sensor associated with one or both of the control unit input and control unit output. When the pumping function of the control unit is not activated, i.e. the control unit is in the passive mode, pressure changes within the plurality of interconnected chambers may be transmitted to one or both of the control unit input and control unit output. Such pressure changes may be referred to as "back pressure" changes. The sensors associated with the input and/or output may detect such back pressure changes and communicate those changes to the control unit. Such an arrangement may provide a self-contained, modular control unit which only requires connection to the plurality of interconnected chambers in order to provide a mattress system as claimed.

The one or more pressure sensors may be located underneath one or more of the plurality of interconnected chambers. The one or more pressure sensors may comprise a pressure sensor mat. The pressure sensor mat may be arranged to detect pressure changes as a user moves around on the plurality of one or more interconnected chambers. The one or more pressure sensors may be configured for wired or wireless communication with the control unit.

The control unit may comprise a memory unit. The memory unit may be arranged to record the pressure readings taken by the pressure sensors. Such information may be useful to provide patient history to a care provider. Additionally, such information may be useful for research purposes. For example, the pressure changes monitored may be compared with the occurrence of pressure ulcers on a given patient, for example to assist in refining the series of pressure changes which is used to select whether the control unit is configured in the passive mode or active mode.

According to a second aspect of the invention there is also provided a method of controlling a mattress system, the method comprising the steps of:

providing a mattress system, the mattress system comprising a plurality of interconnected chambers and a control unit, the mattress system having an active mode in which the control unit is activated to increase and decrease the pressure within the plurality of interconnected chambers, and a passive mode in which the control unit does not increase or decrease the pressure within the plurality of interconnected chambers, the control unit further comprising one or more sensors arranged to detect pressure changes within the plurality of interconnected chambers when the control unit is in the passive mode,

configuring the mattress system into the passive mode,

monitoring the pressure changes in the plurality of interconnected chambers, and

if the detected pressure changes fall within a first set of pressure changes, the control unit generating a first signal, and if the detected pressure changes fall within a second set of pressure changes, the control unit generating a second signal.

The method may further comprise a calibration step, wherein the mattress system has a calibration mode when a patient first lies on a mattress, wherein when in the calibration mode the control unit is configured to increase the pressure within the interconnected chambers to a first pressure, and then allow deflation of the interconnected chambers to a second pressure, and the time taken to deflate from the first pressure to the second pressure is monitored. The control unit may use the deflation time to calculate an approximate weight of the patient.

The control unit may comprise a memory unit, where a database of deflation times is stored, and the control unit may further be configured to compare the detected deflation time to the database of deflation times in order to arrive at an approximation of the weight of a patient. The deflation time, or approximate weight of the patient, may be used to calibration the mattress system, in particular with regards to the determination of the first set of pressure changes and second set of pressure changes. For example, the first set of pressure changes may comprise a series of pressure changes

detected over a set time period, where the pressure changes exceed a threshold value. The threshold value may be adjusted based on the approximate weight of a patient, for example reduced for lighter patients and increased for heavier patients. The calibration step may comprise determining the threshold pressure change value on the basis of the weight of the patient and/or

deflation time.

The use of the calibration mode of the mattress advantageously allows the mattress system to be tailored to the patient lying on the mattress system without requiring any additional user or medical professional input. For example, there is no need to weigh the patient before they get on the bed, and there is no need to input any additional data into the control unit when the patient gets on the bed. The calibration mode allows for the automatic adjustment of the mattress system based on the weight of a patient.

The first set of pressure changes may be chosen to indicate that a patient is moving sufficiently to avoid pressure ulcers. The first signal may command the control unit to remain in the passive mode.

The second set of pressure changes may be chosen to indicate that the patient movement pattern is at risk of pressure ulcers developing. The second signal may command the control unit to enter the active mode, and begin changing the pressure within the plurality of interconnected chambers. The second signal may cause the control unit to emit an alarm signal or notification, for example an audible or visual alarm, or an alert

notification to a care provider. The alert notification may query the care provider, requesting instructions on whether to move the control unit into the active mode. The care provider may send a response signal to the control unit, either having the effect of leaving the control unit in the passive mode, or causing the control unit to enter the active mode. In the event of a non- response to the alert notification in a given time period, the control unit may enter the active mode.

The mattress may further comprise a fall detection mode, wherein if the pressure detected by the pressure sensors suddenly drops, an alarm is activated. The fall detection mode may be an optional mode activated where a patient is bed-bound, as otherwise a more mobile patient may activate the alarm simply when getting out of bed.

According to a third aspect, the invention provides a control unit for a mattress system according to the first aspect of the invention, the control unit

comprising an output, the output configured for

connection to a plurality of interconnected chambers, the output further comprising a sensor, the sensor arranged to detect pressure changes in the plurality of

interconnected chambers when the output is connected to the plurality of interconnected chambers.

The control unit may include any of the features as described in relation to the control unit of the first aspect of the invention. Advantageously, the control unit according to the third aspect of the invention may be retrofitted to existing mattresses to provide a mattress system according to the first aspect of the invention .

According to a fourth aspect, the invention provides a method for measuring the weight of patient lying on a mattress system, the mattress system comprising at least one air-holding chamber connected to a pump unit, the method comprising the steps of activating the pump unit to increase the pressure within the air-holding chamber to a first pressure, allowing the deflation of the air- holding chamber to a second pressure, and monitoring the deflation time between the first pressure and second pressure. The invention may also provide a mattress system, the mattress system comprising at least one air- holding chamber connected to a pump unit, the mattress system comprising a "weigh" mode, in which the mattress is arranged to perform the method as described according to the fourth aspect of the invention. The method may further comprise the step of comparing the deflation time to a calibration table of deflation times, thereby arriving at an approximate weight of the patient.

According to a fifth aspect, the invention provides a method for calibrating a mattress system, the mattress system comprising at least one air-holding chamber connected to a pump unit, the method comprising the steps of a first patient of a known weight lying on the

mattress system, the pump unit inflating the air-holding chamber to a first pressure, allowing the air-holding chamber to deflate to a second pressure and monitoring the deflation time between the first pressure and second pressure, recording the weight of the patient and the associated deflation time, repeating the method steps with a second patient of a known weight, the weight of the second patient being different to that of the first patient. By such a method, and repeating the method steps any number of times, a database of deflation times and patient weights may be compiled.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a schematic view of a mattress system according to a first embodiment of the invention;

Figure 2 shows schematic view of a control unit forming part of the mattress system shown in figure

1;

Figure 3 shows a process diagram for a method of

controlling a mattress system according to a second embodiment of the invention; and

Figure 4 shows a flow chart of a method of operating the mattress system. Detailed Description

Figure 1 shows a mattress system 10 comprising a mattress 12 and a control unit 14. The mattress

comprises a first set of interconnected chambers 16 and second set of interconnected chambers 18. The first set of interconnected chambers 16 is connected to the control unit 14 by a connection tube 20, such that the control unit 14 may increase or decrease the pressure within the first set of interconnected chambers 16. The second set of interconnected chambers 18 is also connected to the control unit 14 by a connection tube 22, such that the control unit 14 may increase or decrease the pressure within the second set of interconnected chambers 18. The first set of interconnected chambers 16 and second set of interconnected chambers 18 may be arranged to be

independently adjustable by the control unit 14 in an active mode, and increase or decrease in pressure in one set of interconnected chambers has no effect on the pressure within the other set of interconnected chambers. The first set of interconnected chambers 16 and second set of interconnected chambers 18 may be arranged to be in fluid communication in a passive mode, where air may pass between the first set of interconnected chambers 16 and second set of interconnected chambers 18. The change between the independent operation and fluid communication may be controlled by a switch, for example a solenoid switch (not shown) in the control unit 14.

The connection tube 20 and connection tube 22 are each joined to the control unit 14 by a connector valve 24, 26. Each connector valve 24, 26, comprises a

pressure sensor 28, 30, the pressure sensors arranged to monitor the backpressure in the interconnected chambers. The mattress system 10 has a first, passive, mode, in which the control unit 14 monitors pressure changes within the plurality of interconnected chambers 16, 18, and a second, active, mode, in which the control unit 14 is used to adjust the pressure levels within the

plurality of interconnected chambers 16, 18.

The pressure sensor 28 is arranged such that when the mattress system is in the first, passive, mode, pressure changes within the first set of interconnected chambers are detected by the sensor 28. The pressure sensor 30 is arranged such that when the mattress system is in the first, passive, mode, pressure changes within the second set of interconnected chambers are detected by the sensor 30. Alternatively, there may be a single back pressure sensor when the first set of interconnected chambers and second set of interconnected chambers are in fluid communication with each other.

The control unit 14 further comprises a pump unit 32. The pump unit 32 is activated by the control unit 14 when in the active mode, in order to increase or decrease the pressure within the plurality of interconnected chambers 16, 18. The control unit 14 is arranged to receive the sensor data obtained by the sensors 28, 30. The control unit 14 further comprises a processor 34, to which the control unit 14 sends the sensor data. The processor 34 analyses the sensor readings, and determines whether they fall within a first set of readings or second set of readings. The first set of readings are chosen such that they represent the patient moving a sufficient amount, both in frequency and type of

movement, that the risk of pressure ulcers is low. For example the first set of readings may comprise the detection of three or more occurrences of pressure changes greater than 2mmHg over an hour long period. The second set of readings are chosen such that they

represent the patient moving an insufficient amount, and the risk of pressure ulcers is high, for example the detection of two or fewer occurrences of pressure changes less than 2mmHg over an hour long period.

In response to the processor 34 categorising the sensor readings in the first set, the pumping function of the control unit 14 is either deactivated, or left inactive, thereby putting the mattress system in the first, passive, mode.

In response to the processor 34 categorising the sensor readings in the second set, two possible responses are available depending on how the control unit 14 has been configured. If the control unit 14 has configured to "automatic" mode, the control unit 14 will

automatically activate the pumping function of the pump unit 32, thereby putting the mattress system in the second, active mode. If the control unit 14 has been configured to "instruct" mode, the control unit 14 will activate an alarm signal via a communications module 36. The communications module 36 may be configured to emit an audible and/or visual alarm, or send a notification signal to a care provider, for example a mobile phone of a nurse, or to a centralised monitoring centre. In response to the alarm, the care provider may decide to initiate the second, active mode of the mattress system 10, for example by pressing a button on the control unit 14 if the care provider is present, or sending an

activation signal to the communications module 36 should the care provider be in a remote location.

Alternatively, the care provider may decide to override the alarm signal, and choose to leave the mattress system 10 in the first, passive, mode. Should the care provider fail to acknowledge the alarm signal, the control unit 14 may be configured to automatically put the mattress system 10 into the second, active, mode after a

predetermined period of time, for example 30 minutes after sending the alarm signal.

The mattress system 10 may further comprise a calibration mode, where the control unit 14 is configured to detect the approximate weight of a patient lying on the mattress 12. In the calibration mode, the control unit 14 may inflate the plurality of interconnected chambers to a first pressure, for example 30mmHg. The control unit 14 is then arranged to allow the deflation of the plurality of interconnected chambers to a second pressure, for example 6mmHg. The control unit is further arranged to monitor the deflation time from the first pressure to the second pressure. The deflation time is dependent on the weight of a patient, and the control unit includes a calibration table with a series of deflation times and associated patient weights. By comparison of the deflation time with the calibration table, the approximate weight of the patient may be determined. Based on the detected deflation time (and associated approximate patient weight) the control unit may adjust the threshold values for the pressure changes which indicate useful movement of a patient. For

example, for a particularly light patient, the threshold pressure value may be reduced, and for a particularly heavy patient, the threshold pressure value may be increased. Therefore, the system may be automatically configured to provide the optimum patient monitoring without requiring any additional input from a user or healthcare professional. Figure 3 shows various processes the mattress system 10 may be configured to undertake. Initially, the sensors 28, 30 in the control unit 14 are arranged such that they monitor the pressure changes in the mattress 100. The processor 34 then analyses the pressure sensor readings 102. If the pressure sensor readings fall within a first set of readings 104, indicating that no action is required, the mattress system 10 remains in the passive mode 106. The process then returns to the monitoring stage 100.

If the pressure sensor readings fall within a second set of readings 108, indicating that the patient is at risk of pressure ulcers, two possible modes may be chosen. If configured for automatic operation, the mattress system is automatically switched to the active mode 110. If configured for "alert" operation, a

notification is sent to a care provider, or an alarm is triggered at the pump unit 112. On receipt of the notification, or on noticing the alarm, the care provider may decide to leave the mattress system in passive mode

114, and the process returns to the monitoring stage 110. Alternatively, the care provider may decide to initiate the active mode of the mattress 116. If no response is received from the care provider within a certain time frame, the control unit 14 may assume that the care provider is unavailable and activate the active mode of the mattress system 116.

Figure 4 is an alternative flow diagram

demonstrating how the mattress system may operate. The method is similar, with the addition of a calibration step at the beginning. Initially, in step 200 a patient lies on a mattress, and the mattress system 10 enters the configuration mode 202. Then the control unit 14 of the mattress system 10 inflates the plurality of chambers 16, 18, to a first pressure, in this case 30mmHg, in step 204. The control unit 14 then allows the plurality of chambers 16, 18, to deflate to a second pressure, in this case 6mmHg, in step 206. The deflation time from the first pressure to the second pressure is monitored, and compared to a table of results stored in the control unit 14. As such, in step 208, the weight of the patient may be obtained. Using the weight of the patient, the method may further comprise calibrating the threshold pressure value which indicates a useful movement, in step 210. The method may then proceed to step 100, as described with reference to figure 3, and carry on as described with reference to figure 3.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different

variations not specifically illustrated herein. By way of example only, certain possible variations will now be described .

The invention may comprise one or more pressure sensor mats located underneath the mattress, and more particularly under one or more of the plurality of interconnected chambers. An example position of a pressure sensor mat 40 is shown in figure 1. The one or more pressure mats may be configured to communicate sensor readings to the control unit via wired or wireless communication. The invention may comprise pressure sensors associated, and mechanically coupled, to the pump unit and pressure sensor pads located underneath the mattress. The processing unit may analyse the pressure sensor readings of both types of pressure sensor when determining whether to activate the active mattress mode.

The invention may also comprise a control unit being retrofitted to an existing mattress, where the existing mattress comprises a plurality of interconnecting

chambers. The control unit may comprise one or more fixing elements, for fixing the control unit in position relative to the mattress. For example, the fixing elements may comprise one or more hooks which may be used to secure the control unit to a bed frame. Therefore, the control unit may be used to convert a conventional mattress to an active/passive mattress system as

described above.

The control unit is preferably electrically powered, and via a mains power connection. However, in an

alternative embodiment the control unit may be battery powered .

The control unit may be programmable via a wired or wireless connection to a computer device. The control unit may be configured to send communications to a smart device, such as a mobile phone or tablet via a pairing process, for example Bluetooth communication.

Alternatively, the control unit may comprise an input panel, for example a keyboard or touchscreen, into which a care provider may input information such as a mobile phone number. The input panel may be configured to present a care provider with a number of options relating to the set up of the control unit, for example whether the control unit was arranged to send an alert signal or enter the active mode automatically.

The plurality of interconnecting chambers may comprise an air-retaining material, for example a foam section. The foam section may comprise cross-sectional profile. Foam present in different chambers of the plurality of interconnecting chambers may have different cross-sectional profiles.

The skilled person will appreciate that whilst the term "mattress" is used, and this will usually be

interpreted to mean a mattress on a bed, the invention is equally applicable to a cushion, seat pad, or seat backrest, and such minor variations are encompassed by the following claims.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable,

advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.